CURRENT PERSPECTIVES
Primary and Secondary Depression: A Review* CHARLES G. COSTELLO, PH.D. I AND CAROL
B. SCOTT,
B.A.2
The literature on the distinction between primary and secondary depression is reviewed. The research data indicate that less severe, non life-threatening suicidal thoughts and behaviours occur more often in patients with secondary depression than in those with primary depression and that the prognosis for secondary depression after somatic forms of therapy is poorer than that for primary depression. The data also suggest that secondary depressives, unlike primary depressives, suffer from chronic dysphoria. It is concluded that, because the available evidence suggests that there are no qualitative differences between the episodes of primary and secondary depression, future research should concentrate on investigating the characteristics of different groups of patients with secondary depression rather than on comparisons between primary and secondary depression in general.
ing, for the sake of comprehensiveness, the studies reviewed by Clayton and Lewis (6) which satisfy the selection criteria listed below. . Munro (7), in his study of familial and social factors involved in depression, appears to have been the first researcher to use the term "primary depression." He noted that, in his research "only patients suffering from primary depressive illness (i.e. with no previous history of psychiatric disorder apart from affective illness or cyclothymic personality) were investigated so as to reduce extraneous psychopathological factors to a minimum." However, the first investigation comparing primary and secondary depressives was reported by Woodruff et al (8). Robins et al (9), noting the chronological aspect of the classification system, described the classes as follows: "a primary affective disorder is one in which the first evidence of diagnosable psychiatric illness is an affective episode; a secondary affective disorder is one in which the affective episode was preceded by another diagnosable psychiatric illness." This definition of secondary depression is known as the Feighner, or St. Louis, definition (10). It takes into account the entire psychiatric history of the individual and assigns the category "secondary" to only those cases whose first psychiatric disorder was a non depressive one. There is a second definition, that of the Research Diagnostic Criteria (RDC) (11), which assigns the category "secondary" when the current episode of depression is preceded by a non depressive psychiatric illness, even though the latter illness may have been preceded by an episode of depression. The RDC definition of primary depression is the more restrictive one: a depressive episode must be the first psychiatric condition to occur in the individual and no episode of depression can be preceded by a nondepressive condition. The Feighner definition of primary depression simply states that a depressive episode must be the first psychiatric condition to occur in the life of the individual but that non depressive conditions may occur before the onset of later episodes of depression. The Feighner definition of secondary depression results in a more homogeneous class of patients, in that a non depressive psychiatric condition must be the first to occur in patients assigned to the class of secondary depressions. On the other hand, according to the RDC definition of secondary depression, only the current episode of depression must be preceded by a non depressive psychiatric condition even though the very first episode may have been depression.
T
he need to reduce the heterogeneity of the major unipolar depressive disorders through some form of sub-classification has been emphasized in recent reviews of various aspects of depression: the role of stress in unipolar depression (1), relapse in unipolar depression (2), and the similarities and differences between community and clinic cases of depression (3). A number of classification systems of unipolar depressions have been proposed: psychotic and neurotic; endogenous and exogenous; spectrum and pure; with and without melancholia; autonomous and reactive; primary and secondary. Two of these classification systems, which are very similar and have been recently reviewed, are depression with and without melancholia (4) and autonomous and reactive depression (5). The primary/secondary classification system does not appear to have been reviewed since the paper by Clayton and Lewis (6). The purpose of this article is to review studies on the primary/secondary distinction includ-
Manuscript received March 1990; revised July 1990. I Professor, Department of Psychology, University of Calgary, Calgary, Alberta. 20 raduate Student, Department of Psychology, University of Calgary, Calgary, Alberta. Address reprint requests to: Dr. Charles O. Costello, Department of Psychology, University of Calgary, 2500 University Drive NW, Calgary, Alberta TIN IN4 Can. J. Psychiatry Vol. 36, April 1991
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As would be expected, the application of the two definitions has produced quite different results. Giles et al (12) found that two-thirds of patients who were classified as having secondary depressions by the RDC were primary depressives according to the Feighner definition. Although the review of the literature does not suggest that the research findings differ according to the definition used, we will identify the definition used in each of the studies reviewed below. The term "secondary depression" has also been considered by some researchers to include depressive disorders preceded by either another psychiatric illness or a non psychiatric illness. However, in this article we shall review only studies that defined secondary depression as one in which the depressive episode was preceded by a diagnosable psychiatric disorder. Depression secondary to non psychiatric illnesses has recently been reviewed (13,14). The studies selected for review in this article also had to satisfy the following criteria: I. the entry point into the study had to be the identification of a group of depressed individuals who were subsequently classified into primary and secondary depressives. Therefore, we have not reviewed studies where the entry point was a non depressive psychiatric disorder such as schizophrenia, alcoholism or anxiety disorder even though data on secondary depression are reported in these studies; 2. although the primary/secondary distinction can be applied to bipolar depressions as well as unipolar depressions (15), most of the research has been done on unipolar depression and, therefore, only studies of unipolar depression were reviewed. We will first review the evidence concerning the ratio of primary to secondary depressions. We will also review the frequency with which secondary depressions are preceded by each of the non depressive psychiatric disorders identified in the studies. We will review the data on the similarities and differences between the two types of depression in their: I. demographic characteristics; 2. symptoms; 3. natural history; 4. family history; 5. neurophysiological characteristics; and 6. response to treatment. In a final section, we will discuss the utility of the distinction on the basis of the evidence reviewed and make some recommendations for research. Ratio of Primary to Secondary Depressions Only three studies involved cases of depression identified in random samples of individuals. One was a community study (16) in which the primary to secondary ratio, using the RDC definition of secondary depression, was found to be 6.3: I. The second (17) was a random sample of inpatients in which the primary to secondary ratio, using the Feighner definition, was 1.5: I. The third (18), which also used the Feighner definition, was a random sample of outpatients for which the ratio was also found to be 1.5: I. Since the community study used the RDC definition, one might have expected the proportion of primary depressives to be smaller than in the studies using the Feighner definition because, as noted previously, the RDC definition for primary depression is a more restrictive one. One possible explanation for the larger proportion of secondary depressives among outpatients
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and inpatients, as Weissman and Myers (16) noted, is that the antecedent conditions probably continue to exist during the depressive episode, and the presence of multiple disorders increases the likelihood of referral to a clinic. Since the remaining studies of outpatients or inpatients did not use random sampling procedures, their findings on the ratio of primary to secondary depressives must be viewed with caution. Some of the studies involved special populations. For instance, Coryell and Turner's (19) sample consisted of depressed outpatients who were selected as likely responders to tricyclic antidepressant treatment, and Berger et al (20) excluded from their study sample "patients with a short-term reactive depression closely connected with a severe traumatic experience as well as patients who had a depressive personality disorder since childhood." As might be expected in view of the various selective biases in the studies of psychiatric outpatients and inpatients (mostly inpatients), the range of ratios of primary to secondary depressives is wide. In the 24 studies in which the Feighner definition of secondary depression was used (6,8,12,17-19,23, 24,27-29,31-35,36,37-40,43,46,47) the range is 0.8: I to 5.9: I, with a mean of 2.3: 1. In the 11 studies in which the RDC definition was used (15,16,20,25,26,30, 36, 37, 42, 44, 45) the range is 0.6: 1 to 6.2: 1 with a mean of 2.4: I. The similarity in the average ratio for the two groups of studies is puzzling because of the differences in the RDC and Feighner definitions of secondary depression. One possible explanation is that what Wood et al (46) refer to as complicated cases - patients who have a depressive episode followed by a non depressive disorder followed by a further depressive episode, that is the patients who increase the heterogeneity of the primary depression group when the Feighner definition is used and who increase the heterogeneity of the secondary depression group when the RDC definition is used are relatively rare. In keeping with this explanation is the finding of Grove et al (33) that the proportions of primary depressions, secondary depressions and complicated cases in the 569 unipolar depressions they studied were 57%, 34% and nine percent, respectively. In summary, it seems that among clinic patients with a diagnosis of unipolar depression, there are approximately 2.5 times as many primary depressives as secondary depressives. Frequencies of Antecedent Non Depressive Psychiatric Disorders Nine of the studies of outpatients and inpatients using the Feighner definition of secondary depression (8,12,27,33,38,39,43,46,47) and seven of the studies using the RDC definition (15,21,26,30,36,42,44) presented the frequencies with which specific non depressive, psychiatric disorders occurred before the onset of depression were given. Despite the differences between the studies in the definition of secondary depression, the selective biases in the samples studied and the changes over time in diagnostic practices, alcoholism and anxiety disorder were antecedent to secondary depression in some of the patients in all of the studies (see Table I). There is no obvious reason why drug
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Table I Conditions Antecedent to Secondary Depression Percentage of Studies
Percentage of Subjects with This Condition
with Subjects Having This Condition
from All Studies'
Feighner Definition
RDC Definition
Feighner Definition
RDC Definition
Alcoholism
100
100
67
71
Anxiety disorders
100
100
78
71
Hysteria/Briquet's syndrome
78
57
67
14
Condition
Schizophrenia"
67
29
22
a
Antisocial personality disorder
67
71
1I
14
Dru abuse
56
100
* two or more diagnoses may occur with the same frequency
a
43
a In the original Feighner definition of secondary depression, schizophrenia was not listed as one of the psychiatric conditions to which depression could be secondary. It was later added to the ROC definition. However, it seems that some researchers, although they have adopted the Feighner definition in its chronological aspects, they have at the same time adopted the ROC definition in relation to the list of possible antecedent non depressive conditions.
abuse should occur as an antecedent in all of the studies when the ROC definition is used but only in a little over one-half of the studies using the Feighner definition. One can also examine the frequency of these diagnoses among the patients within each study, keeping in mind that two or more diagnoses may occur with the same frequency (see Table I). Whether the Feighner or the ROC definition of secondary depression was used, alcoholism and anxiety disorder occurred with the greatest or the second greatest frequency in the samples studied. Hysteria or Briquet's syndrome occurred with the greatest or second greatest frequency in over twothirds of the studies that used the Feighner definition but in less than one-fifth of the studies that used the ROC definition. Schizophrenia was the first or second most frequent disorder in about one-quarter of the studies where the Feighner definition was used, but in none of the studies where the ROC definition was used. On the other hand, drug abuse occurred in first or second place in almost one-half of the studies when the ROC definition was used but in none of the studies using the Feighner definition. There is no obvious reason for the discrepancies in the data in relation to hysteria or schizophrenia. The reason why drug abuse is not frequently found when the Feighner definition is used might be due to the restrictiveness of this definition according to which the non depressive psychiatric disorder must be the first to occur in patients assigned to the class of secondary depressives. In people vulnerable to the development of psychiatric conditions depression probably occurs before drug abuse. Demographic Characteristics Three studies using the Feighner definition found that the primary depressives were significantly older than the secondary depressives on intake (32,43,47). However, six studies using the same definition did not find a significant difference in age (8,12,27,38,39,46). One study using the ROC definition and reporting data on age also did not find a significant
difference in age (41), and another (31) found that secondary depressives were older. Two studies that used the Feighner definition found that significantly more primary depressives than secondary depressives were female (27,32). However four other studies using the Feighner definition (8,12,39,46) and two using the ROC definition (21,41) did not find a significant difference in relation to gender. It is clear that there is no consistent evidence in favour of any demographic differences between patients with primary depression and those with secondary depression. Symptoms of Depression Because of the heterogeneity of the antecedent conditions in secondary depression and because they may still be present during the episode of depression one might expect considerable differences between primary depressives and secondary depressives in the number and nature of their symptoms of psychopathology. Therefore, Andreasen and Winokur's (2l) finding that secondary depressives showed more somatization, anger, hostility and phobic anxiety (using the ROC definition) is not surprising. The more important question is whether or not there are any differences in depressive symptoms per se. Though one study using the Feighner definition (43) found that primary depressives had more trouble with their concentration on admission, another using the Feighner definition (39) and one using the ROC definition (41) found no significant difference between the two groups in the severity of depression on admission. The findings of studies that used the Feighner definition of secondary depression, with one exception (8), suggest that suicidal ideation and behaviour is more prevalent in secondary depressives: Stancer et al (43) found that patients suffering from secondary depression had more thoughts of death; Grove et al (32) found that they had greater suicidal tendencies; Wood et al (46) and Reveley and Reveley (39) found that significantly more of the secondary depressives than primary depressives had attempted suicide. Andreasen and
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Winokur (21) using the ROC definition also found that significantly more of the secondary depressives had attempted suicide. However, Reveley and Reveley found no difference if only life-threatening suicide attempts were considered, and Andreasen and Winokur found that significantly more of the primary depressives made serious, life-threatening suicide attempts. Using the Feighner definition, Brim et al (24) found that, upon hospitalization, suicidal ideation/intent was the most severe symptom in their patients with primary depression but was the first to disappear. Although suicidal ideation/intent was not the most severe symptom upon hospitalization in secondary depressives, it tended to persist after the most severe symptom, latency of verbal response, had remitted. It seems that suicide ideation and suicide attempts, particularly of the less severe, non life-threatening sort, occur more often in secondary depressives. However, these suicidal ideations and behaviours may be part of the antecedent non depressive disorder. One could not conclude that these differences reflect a difference in the nature of the primary and secondary depressive episodes. Unfortunately, the available data do not clearly indicate whether the suicidal thoughts and behaviours occurred before the episode of depression, during the episode or during both the episode and the antecedent illness. Wood et al (46) (Feighner) found that the secondary depressives had a greater preponderance of psychological symptoms than somatic symptoms. However, Stancer et al (43) (Feighner) and Andreasen and Winokur (21) (ROC) found no significant differences in relation to the frequency of occurrence of endogeneous symptoms. One study using the Feighner definition (46) and one using the ROC definition (21) found significantly more pronounced motor retardation in secondary depressives than in primary depressives. However, two other studies using the Feighner definition (8,43) found no difference. One study using the Feighner definition (32) found that the depression in secondary depression was worse in the afternoon, whereas in primary depression it was worse in the morning. Grove et al (Feighner) (32) found that more of the patients with primary depression had been deluded and incapacitated during past episodes of depression. Reveley and Reveley (Feighner) (39) found no difference between the two groups in the number of psychotic symptoms in the current episode. In summary, there is no good evidence to suggest that the natures of secondary depression and primary depression differ in their symptoms. Suicidal thoughts and behaviours of the less serious, non life-threatening kind seem to occur more frequently in secondary depressives than in primary depression, but it is unclear whether they are a component of the secondary depressive episode or the antecedent non depressive psychiatric disorder. Natural History
Two studies using the Feighner definition (32,43) found that the primary depressives were significantly older at the age of first onset of depression. However, one study using
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Feighner (38) and one using ROC (21) found no difference in this respect, and one study using the Feighner definition (12) found that the secondary depressives were significantly older at the age of first onset of depression. Woodruff et al (8) (Feighner) found that significantly more of the patients with primary depression reported that their depression was more of a definite change from their old selves. In keeping with this finding, Brim et al (Feighner) (23) found that the secondary depressives on average reported manifesting 14.3 of 79 symptoms "a lot more than most people" when in their normal and usual state, whereas the comparable figure for the primary depressives was 3.3 of 79 - a significant difference. When comparisons were made for specific symptoms, for 21 of 79 symptoms a significantly greater percentage of the secondary depressives saw themselves as manifesting the symptom "a lot more than most people" when in their normal and usual state. The symptoms were depressed mood, irritability, decreased ability to enjoy things, thoughts of death and dying, thoughts of suicide, suicidal intent, low self-esteem, hopelessness, feelings of inferiority, self-consciousness, difficulty staying asleep, headaches, nausea, forgetfulness, nervousness, bored, beliefs that the future is gloomy, self-blame, low self-confidence, fear of harming oneself, fear oflosing one's mind. The authors suggested that this difference in the usual state self- perceptions does not simply reflect the fact that the secondary depressives had a non depressive psychiatric disorder prior to the onset of depression. It is true that many of the symptoms are usually associated with depression, and the data are in keeping with suggestions made by Brim et al that secondary depressives have a chronic dysphoric condition preceding the onset of major depressive episode. In keeping with this suggestion are the findings of Brim et al (Feighner) (24) which indicate that a number of the symptoms of the secondary depressives were significantly more persistent - subjective tiredness, pessimism,low mood, change in usual interests and suicidal ideation/intent - when followed for an average of 17 days after discharge from hospital. Keller et al (ROC) (36) found that at one year follow-up the secondary depressives showed a significantly higher relapse rate (67%) than the primary depressives (22%). A related finding is that of Martin et al (Feighner) (18), which indicated that there was a significantly higher rate of mortality among secondary depressives than among primary depressives at a seven year follow-up from intake as outpatients. However, as the authors noted, the preceding disorders of alcoholism, antisocial personality disorder and drug addiction were themselves associated with higher mortality rates. A finding that might be considered discordant with the suggestion that the secondary depressives, unlike primary depressives, suffer from chronic dysphoria is that of Andreasen and Winokur (ROC) (21), who found that significantly more of the primary depressives (71 %) than the secondary depressives (31 %) were still on medication at one year follow-up. Three studies using the Feighner definition (27,39,46) found that the duration of the current episode of depression
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was significantly longer in the secondary depressives. However, one study using the Feighner definition (32) and two using the RDC definition (21,41) did not find a significant difference between the two groups. In summary, the only difference between the two groups in terms of natural history is that the secondary depressives, unlike the primary depressives, appear to suffer from a chronic dysphoric condition.
Family History The data reported by Grove et al (Feighner) (37) indicate that, while there was no difference between the primary and secondary depressives in the family histories of primary depression, there was a higher frequency of secondary depression in the families of patients with secondary depression. Two other studies using the Feighner definition (39,43) found no difference between the two groups in the rates of family depression. One study using the RDC definition (15) found no significant difference in this respect. However, another study using the RDC definition (21) found a greater degree of affective disorder in the first degree relatives of secondary depressives. On the basis of the evidence available, there is no difference between the two groups in the degree to which their depression is inherited or in depressogenic family circumstances. Neurophysiological Characteristics
Two studies using the RDC definition (37,41) found that the patients with secondary depression had significantly shorter REM latencies than those with primary depression. But two other studies using the same definition (20,44) and one using the Feighner' definition (12) did not find a significant difference in this respect. Two studies using the Feighner definition (25,27) and two using the RDC definition (42,45) found significantly more nonsuppressors on the Dexamethasone Suppression Test among primary depressives. However, three other studies using the RDC definition (20,26,41) and two using the Feighner definition (12,31) did not find significant differences between primary and secondary depression in this respect. Agren and Niklasson (22) found that patients with primary depression had higher cerebrospinal levels of the indices of brain energy metabolism, creatin and creatinine. In summary, despite Agren and Niklasson's finding which no one appears to have attempted to replicate, there is no evidence supporting a difference in neurophysiological characteristics between primary and secondary depression. Treatment
Andreasen and Winokur (RDC) (21) and Reveley and Reveley (Feighner) (39) did not find any significant differences between the treatments received by patients with primary and secondary depression for their current episode. Grove et al (Feighner) (32) found that significantly more of the primary
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depressives had received ECT for past episodes of depression. Two studies using the Feighner definition (28, 47) reported that primary depressives showed significantly greater improvement than secondary depressives after a course of ECT. One study using the RDC definition (48) found no difference. Two other studies using the Feighner definition (24,39) found significantly greater improvement in patients with primary depression after a course of treatment in which the patients received "some form of somatic treatment," presumably either ECT or antidepressant medication. Coryell and Turner (Feighner) (19) found that primary depressives showed a significantly better response to a six week course of treatment with desipramine and Coryell et al (Feighner) (28) found that primary depressives showed significantly greater improvement at discharge and six months follow-up after a course of hospital treatment other than ECT. The latter study suggested that the poorer outcome in secondary depression was not due simply to the persistence of the symptoms of the antecedent non depressive disorder because it was the depressive symptoms that persisted. Othmer et al (Feighner) (38) and Fava et al (RDC) (30) found no difference between the two types in their response to amitriptyline. However, Othmer et al did find that patients with primary depression responded better than those suffering from secondary depression to bupropion. Fava et al's failure to find a significant difference in the response to amitriptyline may be due to the fact that they investigated only depressed patients with melancholia. In summary, there appears to be a more positive prognosis for primary depression than for secondary depression. This may be because secondary depressives suffer from a chronic dysphoric condition (suggested by the natural history data) or because there is a persistence of the antecedent non depressive psychiatric disorder and a depressive response to that disorder. Conclusion
In his research project, Munro (7) identified a group of patients suffering from primary depression who had no history of non depressive psychiatric disorders, a procedure which needs no defence. Although depressive illnesses are complex and are often preceded by and co-existing with other psychiatric conditions it would be foolhardy to attempt to investigate them in all their complexity. As Banaji and Crowther (49) have noted: "the more complex a phenomenon, the greater the need to study it under controlled conditions, and the less it ought to be studied in its natural complexity." Therefore, it is advisable for researchers wishing to understand the nature of depression itself to include in their research sample a group of subjects who have not had a non depressive psychiatric disorder in the past and are not currently suffering from one. For researchers the most important question in relation to the distinction between primary and secondary depression is whether or not there are differences in the nature of the two types of depression. If the available evidence suggests that
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there are such differences then research pursuing these differences further should be encouraged. There do appear to be some differences between the two groups of individuals with primary depression or secondary depression but there is no clear evidence that these differences are consequences of differences in the natures of the two depressive disorders. The apparent differences are: 1. that suicidal thoughts and behaviours of the less severe non life-threatening sort occur more often in secondary depressives; 2. that secondary depressives, during periods when they are not suffering from a major depressive episode, seem to have more depressive symptoms suggesting the presence of a chronic dysphoric state; 3. that the prognosis for secondary depressives after either treatment with ECT or antidepressant medication appears to be poorer. Suicidologists and researchers interested in the nature of depression might investigate whether the greater prevalence of suicidal thoughts and behaviours in secondary depressives are a component of: 1. the depressive episode itself; 2. the antecedent non depressive condition; or 3. a chronic dysphoric state. Researchers interested in any of the non depressive psychiatric conditions such as alcoholism and anxiety disorders, which are frequently followed by secondary depression, should determine whether or not a chronic dysphoric condition was present before the onset of a major depressive episode. The functional relationship between such a dysphoric condition, the non depressive psychiatric condition and the depressive episode should also be investigated. A particularly important question is whether or not a chronic dysphoric state exists in some individuals which puts them at risk for both depressive episodes and non depressive psychiatric conditions. The reasons for the poorer prognosis after treatment for secondary depression is also worthy of further investigation particularly if it can be demonstrated that it is the depressive episode itself that persists rather than the non depressive condition. It would be interesting to determine whether or not cognitive therapy, which has been shown to reduce relapse in depression (50), might be of particular value for secondary depressives. All of the above suggestions for further research concern aspects of secondary depression. It is this approach rather than comparisons between primary and secondary depression that is likely to prove fruitful because the available evidence suggests that there are no qualitative differences in the natures of primary and secondary depression. Although Giles et al (12) found no differences between secondary depression defined by the Feighner definition and secondary depression defined by the RDC definition, those whose entry point in their research is the identification of individuals with secondary depression should investigate patients with secondary depression identified by the two alternative definitions separately. A more promising research strategy than one which involves the investigation of a general group of secondary depressives with a variety of antecedent non depressive conditions
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21. Andreasen NC, Winokur G. Secondary depression: familial, clinical, and research perspectives. Am J Psychiatry 1979; 136: 62-66. 22. Agren H, Niklasson F. Creatinine and creatine in CSF: indices of brain energy metabolism in depression. J Neural Transm 1988; 74: 55-59. 23. Brim J, Wetzel RD, Reich T, et a1. Primary and secondary affective disorder: Part II. differences in usual state self perceptions. Compr Psychiatry 1980; 21: 388-395. 24. Brim J, Wetzel RD, Reich T, et a!. Primary and secondary . affective disorder: Part III. Longitudinal differences in depression symptoms. J Clin Psychiatry 1984; 45: 64-69. 25. Brown WA, Shuey 1. Response to dexamethasone and subtype of depression. Arch Gen Psychiatry 1980; 37: 747-751. 26. Carroll BJ, Feinberg M, Greden JF, et a!. Diagnosis of endogenous depression: comparison of clinical, research and neuroendocrine criteria. J Affective Disord 1980; 2: 177-194. 27. Coryell W,Gaffney G, Burkhardt PE. DSM-Ill melancholia and the primary-secondary distinction: a comparison of concurrent validity by means of the dexamethasone suppression test. Am J Psychiatry 1982; 139: 120-122. 28. Coryell W, Pfohl B, Zimmerman M. Outcome following ECT - a comparison of primary and secondary depression. ConvulsiveTherapy 1985; I: 10-14. 29. Coryell W, Zimmerman M, Pfohl B. Short-term prognosis in primary and secondary major depression. J Affective Disord 1985; 9: 265-270. 30. Fava GA, Lisansky J, Kellner R, et a!. Treatment responses in primary and secondary melancholia: a preliminary report. J Clin Psychiatry 1985; 46: 332-334. 31. Giles DE, Schlesser MA, Rush AJ. Polysomnographic findings and dexamethasone non suppression in unipolar depression: a replication and extension. Bioi Psychiatry 1987; 22: 872-882. 32. Grove WM, Andreasen NC, Clayton PJ. Primary and secondary affective disorders: baseline characteristics of unipolar patients. J Affective Disord 1987; 13: 249-257. 33. Grove WM, Andreasen NC, Winokur G, et a!. Primary and secondary affective disorders: unipolar patients compared on familial aggregation. Compr Psychiatry 1987; 28: 113-126. 34. Guze SB, Woodruff RA, Clayton PJ. "Secondary" affective disorder - a study of95 cases. Psychol Med 1971; I: 426-428. 35. Guze SB, Woodruff RA, Clayton PJ. The significance of psychotic affective disorders. Arch Gen Psychiatry 1975; 32: 1147-1150. 36. Keller MB, Lavori PW, Lewis CE, et a!. Predictors of relapse in major depressive disorder. JAMA 1983; 250: 3299-3304. 37. Kupfer OJ, Foster FG, Coble P, et a!. The application of EEG sleep for the differential diagnosis of affective disorders. Am J Psychiatry 1978; 135: 69-74. 38. Othmer SC, Othmer E, Preskom SH, et a!. Differential effect of amitriptyline and bupropion on primary and secondary depression: a pilot study. J Clin Psychiatry 1988; 49: 310-312. 39. Reveley AM, Reveley MA. The distinction of primary and secondary affective disorders. J Affective Disord 1981; 3: 273279.
40. Robins E, Gentry KA, Munoz RA, et a!. A contrast of the three or more common illnesses with the ten less common in a study and 18-month follow-up of 314 psychiatric emergency room patients. Part 2. characteristics of patients with the three more common illnesses. Arch Gen Psychiatry 1977; 34: 269-281. 41. Rush AJ, Giles DE, Roffwarg HP, et a!. Sleep EEG and dexamethasone suppression test findings in outpatients with unipolar major depressive disorders. Bioi Psychiatry 1982; 17: 327-341. 42. Schlesser MA, Winokur G, Sherman BM. Hypothalamicpituitary-adrenal axis activity in depressive illness. Arch Gen Psychiatry 1980; 37: 737-743. 43. Stancer HC, Persad E, Joma T. The occurrence of secondary affective disorder in an inpatient population with severe recurrent affective disorder. Br J Psychiatry 1984; 144: 630-635. 44. Thase ME, Kupfer DJ, Spiker DG. Electroencephalographic sleep in secondary depression: a revisit. Bioi Psychiatry 1984; 19: 805-814. 45. Vandewalle J, Charles G, Marden Y, et a!. Dexamethasone resistance and cortisol secretion in depressive illness. Bioi Psychiatry 1983; 18: 385-389. 46. Wood D, Othmer S, Reich T, et at. Primary and secondary affective disorder. 1. past social history and current episodes in 92 depressed inpatients. Compr Psychiatry 1977; 18: 201-210. 47. Zorumski CF, Rutherford JL, Burke WJ, et a!. ECT in primary and secondary depression. J Clin Psychiatry 1986; 47: 298-300. 48. Rich CL, Spiker DG, Jewell SW, et al, DSM-Ill, RDC and ECT: depressive subtypes and immediate response. J Clin Psychiatry 1984; 45: 14-18. 49. Baraji MR, Crowder RG. The bankruptcy ofeveryday memory. Am Psychol1989; 44: 1185-1193. 50. Simons AD, Murphy GE, Levine JL, et a!. Cognitive therapy and pharmacotherapy for depression: sustained improvement over one year. Arch Gen Psychiatry 1986; 43: 43-48.
Resume Les auteurs passent en revue les publications examinant les differences entre la depression primaire et secondaire. Les recherches indiquent que les pensees suicidaires et les comportements de nature moins grave, ne mettant pas la vie en danger, sontplusfrequents chez les deprimes secondaires que primaires, et que le pronostic apres un traitement de type somatique est moins bon pour les deprimes secondaires que primaires. Les donnees suggerent aussi que, contrairement aux deprimes primaires, les deprimes secondaires souffrent de dysphorie chronique. Selon les donnees disponibles, it ne semble pas y avoir de difference qualitative entre les crises de depression primaire et secondaire. On conclut done qu'a l'avenit; les recherches devraient se concentrer sur l' examen des caracteristiques de divers groupes de deprimes secondaires, plutot que sur la comparaison entre les deprimes primaires et secondaires en general.
Primary and Secondary Depression: A Review* CHARLES G. COSTELLO, PH.D. I AND CAROL
B. SCOTT,
B.A.2
The literature on the distinction between primary and secondary depression is reviewed. The research data indicate that less severe, non life-threatening suicidal thoughts and behaviours occur more often in patients with secondary depression than in those with primary depression and that the prognosis for secondary depression after somatic forms of therapy is poorer than that for primary depression. The data also suggest that secondary depressives, unlike primary depressives, suffer from chronic dysphoria. It is concluded that, because the available evidence suggests that there are no qualitative differences between the episodes of primary and secondary depression, future research should concentrate on investigating the characteristics of different groups of patients with secondary depression rather than on comparisons between primary and secondary depression in general.
ing, for the sake of comprehensiveness, the studies reviewed by Clayton and Lewis (6) which satisfy the selection criteria listed below. . Munro (7), in his study of familial and social factors involved in depression, appears to have been the first researcher to use the term "primary depression." He noted that, in his research "only patients suffering from primary depressive illness (i.e. with no previous history of psychiatric disorder apart from affective illness or cyclothymic personality) were investigated so as to reduce extraneous psychopathological factors to a minimum." However, the first investigation comparing primary and secondary depressives was reported by Woodruff et al (8). Robins et al (9), noting the chronological aspect of the classification system, described the classes as follows: "a primary affective disorder is one in which the first evidence of diagnosable psychiatric illness is an affective episode; a secondary affective disorder is one in which the affective episode was preceded by another diagnosable psychiatric illness." This definition of secondary depression is known as the Feighner, or St. Louis, definition (10). It takes into account the entire psychiatric history of the individual and assigns the category "secondary" to only those cases whose first psychiatric disorder was a non depressive one. There is a second definition, that of the Research Diagnostic Criteria (RDC) (11), which assigns the category "secondary" when the current episode of depression is preceded by a non depressive psychiatric illness, even though the latter illness may have been preceded by an episode of depression. The RDC definition of primary depression is the more restrictive one: a depressive episode must be the first psychiatric condition to occur in the individual and no episode of depression can be preceded by a nondepressive condition. The Feighner definition of primary depression simply states that a depressive episode must be the first psychiatric condition to occur in the life of the individual but that non depressive conditions may occur before the onset of later episodes of depression. The Feighner definition of secondary depression results in a more homogeneous class of patients, in that a non depressive psychiatric condition must be the first to occur in patients assigned to the class of secondary depressions. On the other hand, according to the RDC definition of secondary depression, only the current episode of depression must be preceded by a non depressive psychiatric condition even though the very first episode may have been depression.
T
he need to reduce the heterogeneity of the major unipolar depressive disorders through some form of sub-classification has been emphasized in recent reviews of various aspects of depression: the role of stress in unipolar depression (1), relapse in unipolar depression (2), and the similarities and differences between community and clinic cases of depression (3). A number of classification systems of unipolar depressions have been proposed: psychotic and neurotic; endogenous and exogenous; spectrum and pure; with and without melancholia; autonomous and reactive; primary and secondary. Two of these classification systems, which are very similar and have been recently reviewed, are depression with and without melancholia (4) and autonomous and reactive depression (5). The primary/secondary classification system does not appear to have been reviewed since the paper by Clayton and Lewis (6). The purpose of this article is to review studies on the primary/secondary distinction includ-
Manuscript received March 1990; revised July 1990. I Professor, Department of Psychology, University of Calgary, Calgary, Alberta. 20 raduate Student, Department of Psychology, University of Calgary, Calgary, Alberta. Address reprint requests to: Dr. Charles O. Costello, Department of Psychology, University of Calgary, 2500 University Drive NW, Calgary, Alberta TIN IN4 Can. J. Psychiatry Vol. 36, April 1991
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As would be expected, the application of the two definitions has produced quite different results. Giles et al (12) found that two-thirds of patients who were classified as having secondary depressions by the RDC were primary depressives according to the Feighner definition. Although the review of the literature does not suggest that the research findings differ according to the definition used, we will identify the definition used in each of the studies reviewed below. The term "secondary depression" has also been considered by some researchers to include depressive disorders preceded by either another psychiatric illness or a non psychiatric illness. However, in this article we shall review only studies that defined secondary depression as one in which the depressive episode was preceded by a diagnosable psychiatric disorder. Depression secondary to non psychiatric illnesses has recently been reviewed (13,14). The studies selected for review in this article also had to satisfy the following criteria: I. the entry point into the study had to be the identification of a group of depressed individuals who were subsequently classified into primary and secondary depressives. Therefore, we have not reviewed studies where the entry point was a non depressive psychiatric disorder such as schizophrenia, alcoholism or anxiety disorder even though data on secondary depression are reported in these studies; 2. although the primary/secondary distinction can be applied to bipolar depressions as well as unipolar depressions (15), most of the research has been done on unipolar depression and, therefore, only studies of unipolar depression were reviewed. We will first review the evidence concerning the ratio of primary to secondary depressions. We will also review the frequency with which secondary depressions are preceded by each of the non depressive psychiatric disorders identified in the studies. We will review the data on the similarities and differences between the two types of depression in their: I. demographic characteristics; 2. symptoms; 3. natural history; 4. family history; 5. neurophysiological characteristics; and 6. response to treatment. In a final section, we will discuss the utility of the distinction on the basis of the evidence reviewed and make some recommendations for research. Ratio of Primary to Secondary Depressions Only three studies involved cases of depression identified in random samples of individuals. One was a community study (16) in which the primary to secondary ratio, using the RDC definition of secondary depression, was found to be 6.3: I. The second (17) was a random sample of inpatients in which the primary to secondary ratio, using the Feighner definition, was 1.5: I. The third (18), which also used the Feighner definition, was a random sample of outpatients for which the ratio was also found to be 1.5: I. Since the community study used the RDC definition, one might have expected the proportion of primary depressives to be smaller than in the studies using the Feighner definition because, as noted previously, the RDC definition for primary depression is a more restrictive one. One possible explanation for the larger proportion of secondary depressives among outpatients
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and inpatients, as Weissman and Myers (16) noted, is that the antecedent conditions probably continue to exist during the depressive episode, and the presence of multiple disorders increases the likelihood of referral to a clinic. Since the remaining studies of outpatients or inpatients did not use random sampling procedures, their findings on the ratio of primary to secondary depressives must be viewed with caution. Some of the studies involved special populations. For instance, Coryell and Turner's (19) sample consisted of depressed outpatients who were selected as likely responders to tricyclic antidepressant treatment, and Berger et al (20) excluded from their study sample "patients with a short-term reactive depression closely connected with a severe traumatic experience as well as patients who had a depressive personality disorder since childhood." As might be expected in view of the various selective biases in the studies of psychiatric outpatients and inpatients (mostly inpatients), the range of ratios of primary to secondary depressives is wide. In the 24 studies in which the Feighner definition of secondary depression was used (6,8,12,17-19,23, 24,27-29,31-35,36,37-40,43,46,47) the range is 0.8: I to 5.9: I, with a mean of 2.3: 1. In the 11 studies in which the RDC definition was used (15,16,20,25,26,30, 36, 37, 42, 44, 45) the range is 0.6: 1 to 6.2: 1 with a mean of 2.4: I. The similarity in the average ratio for the two groups of studies is puzzling because of the differences in the RDC and Feighner definitions of secondary depression. One possible explanation is that what Wood et al (46) refer to as complicated cases - patients who have a depressive episode followed by a non depressive disorder followed by a further depressive episode, that is the patients who increase the heterogeneity of the primary depression group when the Feighner definition is used and who increase the heterogeneity of the secondary depression group when the RDC definition is used are relatively rare. In keeping with this explanation is the finding of Grove et al (33) that the proportions of primary depressions, secondary depressions and complicated cases in the 569 unipolar depressions they studied were 57%, 34% and nine percent, respectively. In summary, it seems that among clinic patients with a diagnosis of unipolar depression, there are approximately 2.5 times as many primary depressives as secondary depressives. Frequencies of Antecedent Non Depressive Psychiatric Disorders Nine of the studies of outpatients and inpatients using the Feighner definition of secondary depression (8,12,27,33,38,39,43,46,47) and seven of the studies using the RDC definition (15,21,26,30,36,42,44) presented the frequencies with which specific non depressive, psychiatric disorders occurred before the onset of depression were given. Despite the differences between the studies in the definition of secondary depression, the selective biases in the samples studied and the changes over time in diagnostic practices, alcoholism and anxiety disorder were antecedent to secondary depression in some of the patients in all of the studies (see Table I). There is no obvious reason why drug
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PRIMARY AND SECONDARY DEPRESSION
Table I Conditions Antecedent to Secondary Depression Percentage of Studies
Percentage of Subjects with This Condition
with Subjects Having This Condition
from All Studies'
Feighner Definition
RDC Definition
Feighner Definition
RDC Definition
Alcoholism
100
100
67
71
Anxiety disorders
100
100
78
71
Hysteria/Briquet's syndrome
78
57
67
14
Condition
Schizophrenia"
67
29
22
a
Antisocial personality disorder
67
71
1I
14
Dru abuse
56
100
* two or more diagnoses may occur with the same frequency
a
43
a In the original Feighner definition of secondary depression, schizophrenia was not listed as one of the psychiatric conditions to which depression could be secondary. It was later added to the ROC definition. However, it seems that some researchers, although they have adopted the Feighner definition in its chronological aspects, they have at the same time adopted the ROC definition in relation to the list of possible antecedent non depressive conditions.
abuse should occur as an antecedent in all of the studies when the ROC definition is used but only in a little over one-half of the studies using the Feighner definition. One can also examine the frequency of these diagnoses among the patients within each study, keeping in mind that two or more diagnoses may occur with the same frequency (see Table I). Whether the Feighner or the ROC definition of secondary depression was used, alcoholism and anxiety disorder occurred with the greatest or the second greatest frequency in the samples studied. Hysteria or Briquet's syndrome occurred with the greatest or second greatest frequency in over twothirds of the studies that used the Feighner definition but in less than one-fifth of the studies that used the ROC definition. Schizophrenia was the first or second most frequent disorder in about one-quarter of the studies where the Feighner definition was used, but in none of the studies where the ROC definition was used. On the other hand, drug abuse occurred in first or second place in almost one-half of the studies when the ROC definition was used but in none of the studies using the Feighner definition. There is no obvious reason for the discrepancies in the data in relation to hysteria or schizophrenia. The reason why drug abuse is not frequently found when the Feighner definition is used might be due to the restrictiveness of this definition according to which the non depressive psychiatric disorder must be the first to occur in patients assigned to the class of secondary depressives. In people vulnerable to the development of psychiatric conditions depression probably occurs before drug abuse. Demographic Characteristics Three studies using the Feighner definition found that the primary depressives were significantly older than the secondary depressives on intake (32,43,47). However, six studies using the same definition did not find a significant difference in age (8,12,27,38,39,46). One study using the ROC definition and reporting data on age also did not find a significant
difference in age (41), and another (31) found that secondary depressives were older. Two studies that used the Feighner definition found that significantly more primary depressives than secondary depressives were female (27,32). However four other studies using the Feighner definition (8,12,39,46) and two using the ROC definition (21,41) did not find a significant difference in relation to gender. It is clear that there is no consistent evidence in favour of any demographic differences between patients with primary depression and those with secondary depression. Symptoms of Depression Because of the heterogeneity of the antecedent conditions in secondary depression and because they may still be present during the episode of depression one might expect considerable differences between primary depressives and secondary depressives in the number and nature of their symptoms of psychopathology. Therefore, Andreasen and Winokur's (2l) finding that secondary depressives showed more somatization, anger, hostility and phobic anxiety (using the ROC definition) is not surprising. The more important question is whether or not there are any differences in depressive symptoms per se. Though one study using the Feighner definition (43) found that primary depressives had more trouble with their concentration on admission, another using the Feighner definition (39) and one using the ROC definition (41) found no significant difference between the two groups in the severity of depression on admission. The findings of studies that used the Feighner definition of secondary depression, with one exception (8), suggest that suicidal ideation and behaviour is more prevalent in secondary depressives: Stancer et al (43) found that patients suffering from secondary depression had more thoughts of death; Grove et al (32) found that they had greater suicidal tendencies; Wood et al (46) and Reveley and Reveley (39) found that significantly more of the secondary depressives than primary depressives had attempted suicide. Andreasen and
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Winokur (21) using the ROC definition also found that significantly more of the secondary depressives had attempted suicide. However, Reveley and Reveley found no difference if only life-threatening suicide attempts were considered, and Andreasen and Winokur found that significantly more of the primary depressives made serious, life-threatening suicide attempts. Using the Feighner definition, Brim et al (24) found that, upon hospitalization, suicidal ideation/intent was the most severe symptom in their patients with primary depression but was the first to disappear. Although suicidal ideation/intent was not the most severe symptom upon hospitalization in secondary depressives, it tended to persist after the most severe symptom, latency of verbal response, had remitted. It seems that suicide ideation and suicide attempts, particularly of the less severe, non life-threatening sort, occur more often in secondary depressives. However, these suicidal ideations and behaviours may be part of the antecedent non depressive disorder. One could not conclude that these differences reflect a difference in the nature of the primary and secondary depressive episodes. Unfortunately, the available data do not clearly indicate whether the suicidal thoughts and behaviours occurred before the episode of depression, during the episode or during both the episode and the antecedent illness. Wood et al (46) (Feighner) found that the secondary depressives had a greater preponderance of psychological symptoms than somatic symptoms. However, Stancer et al (43) (Feighner) and Andreasen and Winokur (21) (ROC) found no significant differences in relation to the frequency of occurrence of endogeneous symptoms. One study using the Feighner definition (46) and one using the ROC definition (21) found significantly more pronounced motor retardation in secondary depressives than in primary depressives. However, two other studies using the Feighner definition (8,43) found no difference. One study using the Feighner definition (32) found that the depression in secondary depression was worse in the afternoon, whereas in primary depression it was worse in the morning. Grove et al (Feighner) (32) found that more of the patients with primary depression had been deluded and incapacitated during past episodes of depression. Reveley and Reveley (Feighner) (39) found no difference between the two groups in the number of psychotic symptoms in the current episode. In summary, there is no good evidence to suggest that the natures of secondary depression and primary depression differ in their symptoms. Suicidal thoughts and behaviours of the less serious, non life-threatening kind seem to occur more frequently in secondary depressives than in primary depression, but it is unclear whether they are a component of the secondary depressive episode or the antecedent non depressive psychiatric disorder. Natural History
Two studies using the Feighner definition (32,43) found that the primary depressives were significantly older at the age of first onset of depression. However, one study using
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Feighner (38) and one using ROC (21) found no difference in this respect, and one study using the Feighner definition (12) found that the secondary depressives were significantly older at the age of first onset of depression. Woodruff et al (8) (Feighner) found that significantly more of the patients with primary depression reported that their depression was more of a definite change from their old selves. In keeping with this finding, Brim et al (Feighner) (23) found that the secondary depressives on average reported manifesting 14.3 of 79 symptoms "a lot more than most people" when in their normal and usual state, whereas the comparable figure for the primary depressives was 3.3 of 79 - a significant difference. When comparisons were made for specific symptoms, for 21 of 79 symptoms a significantly greater percentage of the secondary depressives saw themselves as manifesting the symptom "a lot more than most people" when in their normal and usual state. The symptoms were depressed mood, irritability, decreased ability to enjoy things, thoughts of death and dying, thoughts of suicide, suicidal intent, low self-esteem, hopelessness, feelings of inferiority, self-consciousness, difficulty staying asleep, headaches, nausea, forgetfulness, nervousness, bored, beliefs that the future is gloomy, self-blame, low self-confidence, fear of harming oneself, fear oflosing one's mind. The authors suggested that this difference in the usual state self- perceptions does not simply reflect the fact that the secondary depressives had a non depressive psychiatric disorder prior to the onset of depression. It is true that many of the symptoms are usually associated with depression, and the data are in keeping with suggestions made by Brim et al that secondary depressives have a chronic dysphoric condition preceding the onset of major depressive episode. In keeping with this suggestion are the findings of Brim et al (Feighner) (24) which indicate that a number of the symptoms of the secondary depressives were significantly more persistent - subjective tiredness, pessimism,low mood, change in usual interests and suicidal ideation/intent - when followed for an average of 17 days after discharge from hospital. Keller et al (ROC) (36) found that at one year follow-up the secondary depressives showed a significantly higher relapse rate (67%) than the primary depressives (22%). A related finding is that of Martin et al (Feighner) (18), which indicated that there was a significantly higher rate of mortality among secondary depressives than among primary depressives at a seven year follow-up from intake as outpatients. However, as the authors noted, the preceding disorders of alcoholism, antisocial personality disorder and drug addiction were themselves associated with higher mortality rates. A finding that might be considered discordant with the suggestion that the secondary depressives, unlike primary depressives, suffer from chronic dysphoria is that of Andreasen and Winokur (ROC) (21), who found that significantly more of the primary depressives (71 %) than the secondary depressives (31 %) were still on medication at one year follow-up. Three studies using the Feighner definition (27,39,46) found that the duration of the current episode of depression
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was significantly longer in the secondary depressives. However, one study using the Feighner definition (32) and two using the RDC definition (21,41) did not find a significant difference between the two groups. In summary, the only difference between the two groups in terms of natural history is that the secondary depressives, unlike the primary depressives, appear to suffer from a chronic dysphoric condition.
Family History The data reported by Grove et al (Feighner) (37) indicate that, while there was no difference between the primary and secondary depressives in the family histories of primary depression, there was a higher frequency of secondary depression in the families of patients with secondary depression. Two other studies using the Feighner definition (39,43) found no difference between the two groups in the rates of family depression. One study using the RDC definition (15) found no significant difference in this respect. However, another study using the RDC definition (21) found a greater degree of affective disorder in the first degree relatives of secondary depressives. On the basis of the evidence available, there is no difference between the two groups in the degree to which their depression is inherited or in depressogenic family circumstances. Neurophysiological Characteristics
Two studies using the RDC definition (37,41) found that the patients with secondary depression had significantly shorter REM latencies than those with primary depression. But two other studies using the same definition (20,44) and one using the Feighner' definition (12) did not find a significant difference in this respect. Two studies using the Feighner definition (25,27) and two using the RDC definition (42,45) found significantly more nonsuppressors on the Dexamethasone Suppression Test among primary depressives. However, three other studies using the RDC definition (20,26,41) and two using the Feighner definition (12,31) did not find significant differences between primary and secondary depression in this respect. Agren and Niklasson (22) found that patients with primary depression had higher cerebrospinal levels of the indices of brain energy metabolism, creatin and creatinine. In summary, despite Agren and Niklasson's finding which no one appears to have attempted to replicate, there is no evidence supporting a difference in neurophysiological characteristics between primary and secondary depression. Treatment
Andreasen and Winokur (RDC) (21) and Reveley and Reveley (Feighner) (39) did not find any significant differences between the treatments received by patients with primary and secondary depression for their current episode. Grove et al (Feighner) (32) found that significantly more of the primary
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depressives had received ECT for past episodes of depression. Two studies using the Feighner definition (28, 47) reported that primary depressives showed significantly greater improvement than secondary depressives after a course of ECT. One study using the RDC definition (48) found no difference. Two other studies using the Feighner definition (24,39) found significantly greater improvement in patients with primary depression after a course of treatment in which the patients received "some form of somatic treatment," presumably either ECT or antidepressant medication. Coryell and Turner (Feighner) (19) found that primary depressives showed a significantly better response to a six week course of treatment with desipramine and Coryell et al (Feighner) (28) found that primary depressives showed significantly greater improvement at discharge and six months follow-up after a course of hospital treatment other than ECT. The latter study suggested that the poorer outcome in secondary depression was not due simply to the persistence of the symptoms of the antecedent non depressive disorder because it was the depressive symptoms that persisted. Othmer et al (Feighner) (38) and Fava et al (RDC) (30) found no difference between the two types in their response to amitriptyline. However, Othmer et al did find that patients with primary depression responded better than those suffering from secondary depression to bupropion. Fava et al's failure to find a significant difference in the response to amitriptyline may be due to the fact that they investigated only depressed patients with melancholia. In summary, there appears to be a more positive prognosis for primary depression than for secondary depression. This may be because secondary depressives suffer from a chronic dysphoric condition (suggested by the natural history data) or because there is a persistence of the antecedent non depressive psychiatric disorder and a depressive response to that disorder. Conclusion
In his research project, Munro (7) identified a group of patients suffering from primary depression who had no history of non depressive psychiatric disorders, a procedure which needs no defence. Although depressive illnesses are complex and are often preceded by and co-existing with other psychiatric conditions it would be foolhardy to attempt to investigate them in all their complexity. As Banaji and Crowther (49) have noted: "the more complex a phenomenon, the greater the need to study it under controlled conditions, and the less it ought to be studied in its natural complexity." Therefore, it is advisable for researchers wishing to understand the nature of depression itself to include in their research sample a group of subjects who have not had a non depressive psychiatric disorder in the past and are not currently suffering from one. For researchers the most important question in relation to the distinction between primary and secondary depression is whether or not there are differences in the nature of the two types of depression. If the available evidence suggests that
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there are such differences then research pursuing these differences further should be encouraged. There do appear to be some differences between the two groups of individuals with primary depression or secondary depression but there is no clear evidence that these differences are consequences of differences in the natures of the two depressive disorders. The apparent differences are: 1. that suicidal thoughts and behaviours of the less severe non life-threatening sort occur more often in secondary depressives; 2. that secondary depressives, during periods when they are not suffering from a major depressive episode, seem to have more depressive symptoms suggesting the presence of a chronic dysphoric state; 3. that the prognosis for secondary depressives after either treatment with ECT or antidepressant medication appears to be poorer. Suicidologists and researchers interested in the nature of depression might investigate whether the greater prevalence of suicidal thoughts and behaviours in secondary depressives are a component of: 1. the depressive episode itself; 2. the antecedent non depressive condition; or 3. a chronic dysphoric state. Researchers interested in any of the non depressive psychiatric conditions such as alcoholism and anxiety disorders, which are frequently followed by secondary depression, should determine whether or not a chronic dysphoric condition was present before the onset of a major depressive episode. The functional relationship between such a dysphoric condition, the non depressive psychiatric condition and the depressive episode should also be investigated. A particularly important question is whether or not a chronic dysphoric state exists in some individuals which puts them at risk for both depressive episodes and non depressive psychiatric conditions. The reasons for the poorer prognosis after treatment for secondary depression is also worthy of further investigation particularly if it can be demonstrated that it is the depressive episode itself that persists rather than the non depressive condition. It would be interesting to determine whether or not cognitive therapy, which has been shown to reduce relapse in depression (50), might be of particular value for secondary depressives. All of the above suggestions for further research concern aspects of secondary depression. It is this approach rather than comparisons between primary and secondary depression that is likely to prove fruitful because the available evidence suggests that there are no qualitative differences in the natures of primary and secondary depression. Although Giles et al (12) found no differences between secondary depression defined by the Feighner definition and secondary depression defined by the RDC definition, those whose entry point in their research is the identification of individuals with secondary depression should investigate patients with secondary depression identified by the two alternative definitions separately. A more promising research strategy than one which involves the investigation of a general group of secondary depressives with a variety of antecedent non depressive conditions
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Resume Les auteurs passent en revue les publications examinant les differences entre la depression primaire et secondaire. Les recherches indiquent que les pensees suicidaires et les comportements de nature moins grave, ne mettant pas la vie en danger, sontplusfrequents chez les deprimes secondaires que primaires, et que le pronostic apres un traitement de type somatique est moins bon pour les deprimes secondaires que primaires. Les donnees suggerent aussi que, contrairement aux deprimes primaires, les deprimes secondaires souffrent de dysphorie chronique. Selon les donnees disponibles, it ne semble pas y avoir de difference qualitative entre les crises de depression primaire et secondaire. On conclut done qu'a l'avenit; les recherches devraient se concentrer sur l' examen des caracteristiques de divers groupes de deprimes secondaires, plutot que sur la comparaison entre les deprimes primaires et secondaires en general.
