Brain (1978), 101, 495-511
FACTORS INFLUENCING THE RISK OF MULTIPLE SCLEROSIS DEVELOPING IN PATIENTS WITH OPTIC NEURITIS by D. A. S. COMPSTON, J. R. BATCHELOR, C. J. EARL and W. I. MCDONALD
INTRODUCTION
THE clinical syndrome of optic or retrobulbar neuritis (ON) is easily recognized in the typical case. After the exclusion of specific causes there remains a sizeable group of patients in whom the aetiology can not be identified (McDonald, 1977). Some of this latter group develop multiple sclerosis (MS) but the fact that after lengthy follow-up some patients do not have further neurological episodes suggests that isolated optic neuritis is more than one disease. Optic Neuritis and Multiple Sclerosis The statistics which relate optic neuritis to MS are complex. Some facts are well established: approximately 50 per cent of MS patients have a clinical episode of optic neuritis at some time during the course of their disease (McAlpine, Compston and Lumsden, 1955). Many of the remainder have ophthalmoscopic evidence of damage to the optic nerve and there is electrophysiological evidence of past optic neuritis in 90 per cent of clinically definite MS cases (Halliday, McDonald and Mushin, 1973). All of Lumsden's (1970) 36 unselected necropsies on MS patients showed optic nerve demyelination. Except in Japanese studies optic neuritis is the presenting symptom in approximately 20 per cent of cases (Leibowitz and Alter, 1973). The risk of MS developing later in patients with isolated optic neuritis is however less certain: the published incidence varies between 85 per cent (Lynn, 1959) and 13 per cent (Kurland, Auth, Beebe, Kurtzke, Lessell, Nagler and Nefzger, 1963). Several factors may contribute to these differences. First, diagnostic criteria for MS and optic neuritis, and the mean length of follow-up, vary between different studies. Bradley and Whitty (1968) found that cases developing MS after optic neuritis had declared themselves within four years, whereas McAlpine, Lumsden and Acheson (1965) concluded 'The longer the period of observation the higher
Downloaded from http://brain.oxfordjournals.org/ by guest on June 9, 2016
(From the Mclndoe Memorial Research Unit, East Grinstead, Moorfields Eye Hospital and the Institute of Neurology, Queen Square)
496
D. A. S. COMPSTON AND OTHERS
Downloaded from http://brain.oxfordjournals.org/ by guest on June 9, 2016
will be the percentage of cases of retrobulbar neuritis which develop signs of MS'. Since therefore the rate at which patients develop MS is unpredictable a comparison of the mean duration of follow-up between studies may not be useful. Secondly, the methods of analysis vary in different investigations. In most, the proportion of cases developing MS has been determined on the basis of the subsequent course. However, Nikoskelainen and Riekkinen (1974) also included patients who, when first seen with optic neuritis, had disseminated neurological signs or a history of past neurological symptoms. In the most recent study from Belfast, Hutchinson (1976) predicted on the basis of an actuarial analysis that 78 per cent of patients presenting with optic neuritis will have developed MS after fifteen years. Finally, the lower proportion of cases of optic neuritis developing MS in all series reported from the United States, compared with studies from Europe, suggests that there may be real differences in the risk of developing MS and that some of these differences may have a geographical basis. There have been a number of attempts to identify factors which might help to determine the risk of MS developing in the individual patient. Taub and Rucker (1954) investigated the effect of age of onset and found that the risk was marginally increased in those over the age of 20 years, when compared with younger patients. The effect on prognosis of bilateral as opposed to unilateral attacks was studied by Hierons and Lyle (1959). They found no suggestion that bilateral involvement carried a greater risk, irrespective of whether the two eyes were affected simultaneously or sequentially. They did not study recurrent unilateral cases. A number of investigators have noted a slight increase in the attack rate of optic neuritis in the spring and early summer but this seasonal variation has not hitherto proved to be of prognostic value (Taub and Rucker, 1954; Bradley and Whitty, 1967; Hutchinson, 1976). Genetic predisposition to multiple sclerosis has not previously been investigated as a risk factor in patients with optic neuritis. The observation that the proportion of affected first degree relatives of MS patients is twenty times higher than expected (McAlpine et al, 1965) has led to attempts to identify markers of genetic susceptibility to the disease. Until recently such investigations have been unsuccessful. However, the recent discovery of an association between certain tissue types and MS raises the possibility that tissue typing, at the time of the first neurological episode, might be useful in identifying those patients likely to develop disseminated lesions later. We have explored this possibility in patients presenting with isolated optic neuritis. In order to understand our approach to the present investigation it will be helpful to review the current state of knowledge of the major histocompatibility system in man and its relationship to MS.
RISK FACTORS IN MULTIPLE SCLEROSIS
497
HLA and Multiple Sclerosis MS was originally shown to be associated with the presence of HLA-A3 and HLA-B7 (Jersild, Svejgaard and Fog, 1972) but the association is weak. It is now thought that these associations are secondary and that an allele at an adjacent locus confers susceptibility to the disease. In many genetic systems an association between particular alleles does not usually occur in randomly mating populations. However in the HLA system there is a tendency for certain alleles (for example, HLA-A3 and -B7) to occur together more frequently than would be expected by chance alone. The biological importance of this phenomenon, known as linkage disequilibrium, has been discussed by McDevitt and Bodmer (1974). In relation to MS, the practical problem is to distinguish between the locus which codes for the
Downloaded from http://brain.oxfordjournals.org/ by guest on June 9, 2016
The Human Leucocyte Antigen System (HLA) Tissue compatibility is now known to be genetically determined. As in all genetic systems it is the gene products—in this case the HLA antigens—which confer specificity. The HLA antigens are coded for by genes occurring at four sites or loci on the sixth chromosome. There is one locus each for the HLA-A, -B, -C and -D genes (Svejgaard, Hauge, Jersild, Platz, Ryder, Staub Nielson and Thomsen, 1975). There are many alternative gene forms or alleles for each locus. Since the cells of each individual have paired chromosomes they will express only two antigens coded for at each of these four loci. Other genes are found in the same region and attention has recently been concentrated on a group of antigens which are mainly expressed on peripheral blood B-lymphocytes. These antigens are of interest because the genes coding for them are thought to be analogous to genes in mice which are involved in the control of the immune response (Svejgaard et ai, 1975). The murine antigens have been called immune response associated (la) and the human, la-like, antigens. The HLA-A, -B and -C antigens are detected by serological tests on unfractionated peripheral blood lymphocytes (60-80 per cent T-lymphocytes) whereas the la-like antigens are detected by similar tests on purified peripheral blood B-lymphocytes. The detection of HLA-D antigens is more difficult and depends on techniques involving cellular interaction. The definition of some antigens is still provisional and these are identified by the suffix 'w', for example, HLA-Dw2. Recently it has been shown that the la-like and the HLA-Dw antigens are very closely related and may indeed be identical, despite the fact that they are detected by different techniques. Since the evidence is conflicting the WHO Committee on HLA nomenclature has decided to call the la-like antigens HLA-D Related w (HLA-DRw) antigens {Histocompatibility Testing, 1977). In addition to these internationally accepted antigens a number of individual laboratories have defined la-like antigens. Many of these are known to be equivalent to WHO-assigned HLA-DRw antigens, but in other cases, the relationship is still uncertain.
498
D. A. S. COMPSTON AND OTHERS
PATIENTS The patients in this study had all attended the Physicians' Clinic at Moorfields Eye Hospital, City Road or High Holborn, during the past twenty-three years. They were identified by reviewing all the accessible notes. All available patients in whom a clinical diagnosis of optic neuritis had been made and in whom there was no record of neurological symptoms preceding the episode of visual impairment or signs at the time of presentation were asked to reattend the Clinic. As in our previous investigations, optic neuritis was diagnosed in patients presenting with the rapid onset of visual loss, usually accompanied by ocular pain on movement, in whom there was a reduction in visual acuity, with a central field defect, either with or without a swollen disc (Earl and Martin, 1967; Gould, Bird, Leaver and McDonald, 1977). Patients were excluded if they had a retinal lesion or if there was evidence of a condition other than MS which might cause an optic nerve lesion—for example, gross paranasal sinus disease, blood pressure over 180/110 mmHg or hypertensive retinal vascular disease, diabetes, a history of amaurosis fugax, rheumatic valvular heart disease, a family history of optic nerve disease, heavy tobacco or alcohol consumption, dietary deficiency, Vitamin B12 deficiency, regular use of drugs known to cause optic atrophy, hypercholesterotemia, syphilis, long-standing visual loss from other causes, patients with a clinical picture suggestive of ischamic optic neuropathy (Boghen and Glazer, 1975), patients who were
Downloaded from http://brain.oxfordjournals.org/ by guest on June 9, 2016
allele responsible for susceptibility and the loci which code for alleles showing secondary associations due to linkage disequilibrium. The allele showing the highest association is the best candidate for the role of susceptibility gene. HLA-D antigens were therefore studied and Jersild, Hansen, Svejgaard, Fog, Thomsen and Dupont (1973) demonstrated a stronger association between MS and HLA-Dw2 (original local name Ld7a). The development of relatively convenient and reliable techniques for detecting HLA-DRw antigens has stimulated the search for associations between these antigens and MS. The disease has now been shown to be most closely associated with three locally defined la-like antigens —Ag7a (Winchester, Ebers, Fu, Espinosa, Zabriskie and Kunkel, 1975), B group 4 (Terasaki, Park, Opelz and Ting, 1976) and BT 101 (Compston, Batchelor and McDonald, 1976)—and also with HLA-DRw2 {Histocompatibility Testing, 1977). In our own series of 156 MS cases BT 101 was present in 79 per cent compared with a frequency of 35 per cent in 85 controls. These HLA-DRw antigen associations with MS have now been confirmed in patients of Northern European stock, in Europe, Australia and North America {Histocompatibility Testing, 1977). By contrast, in Jordanian Arabs (Kurdi, Ayesh, Abdallat, Maayta, McDonald, Compston and Batchelor, 1977) and in Italians {Histocompatibility Testing, 1977) MS has been found to associate with a specifically different allele, HLA-DRw4. The question we have tried to answer in this study is whether HLA typing provides a useful guide to the risk of development of MS. Arnason, Fuller, Lehrich and Wray (1974) showed that HLA-A3 was present in a higher proportion of patients with MS than in patients with optic neuritis who had not developed MS during follow-up. The present investigation was designed to assess the prognostic significance of the presence of the antigen BT 101. We also assessed the importance of recurrent or bilateral episodes and the season of onset of optic neuritis.
RISK FACTORS IN MULTIPLE SCLEROSIS
499
IMMUNOLOGY HLA typing was done using well validated antisera against the HLA-A, -B and -C gene products in both the National Institutes of Health and a local lymphocytotoxicity test (Batchelor, 1973). HLADRw typing was done on cell populations enriched for B-lymphocytes by first separating lymphocytes from peripheral blood, anticoagulated with edetic acid (EDTA) by centrifugation over a density gradient of Ficoll-Triosil (metrizoate sodium). The cells were then washed in 5 Mm EDTA and incubated with papain treated sheep red blood cells (SRBCs) at 4° C overnight to form E rosettes. The rosetted T-lymphocytes were separated from the non-rosetted B-lymphocytes, macrophages and monocytes by further centrifugation over Ficoll-Triosil. The 'non-rosetted' cells were harvested, washed and resuspended in McCoy's medium with 0-5 per cent foetal calf serum. This suspension contained 80-90 per cent B-lymphocytes as judged by the uptake of fluorescent labelled anti-immunoglobulin. T-lymphocytes from the same blood samples were prepared by lysing the SRBCs in the separated E rosettes with 0-85 per cent ammonium chloride, and then washing and resuspending the lymphocytes as described for the B-lymphocytes. This suspension contained 99 per cent T-lymphocytes as judged by 're-rosetting'. T and B enriched cell suspensions from the same peripheral blood sample were always tested in parallel in lymphocytotoxicity tests in which 1 /A of target cell suspension (4x10* cells/ml) was incubated with a similar volume of antiserum for one hour at 20° C. The cells were then re-incubated with 5 ftl rabbit complement for two hours. 0-4 per cent trypan blue was used to assay cell death. Antisera for HLADRw typing were absorbed with pooled platelets (10lo/ml) three times at 4° C to remove antibodies directed against HLA-A, -B or -C gene products and all sera used to identify HLA-DRw antigens were shown after absorption to react with B- but not T-lymphocytes from the same blood sample. The cells from all patients were tested against antisera defining many HLA-A, -B, -C and -DRw antigens but in this paper the results are given only for the antigens HLA-B7 and BT101. This la-like antigen is equivalent to HLA-DRw2 but also cross-reacts with HLA-DRw 1 and some HLA-DRw6 positive cells.
Downloaded from http://brain.oxfordjournals.org/ by guest on June 9, 2016
not aged between 10 and 50 years at the onset of symptoms and patients in whom the symptoms developed outside Europe, or who were not Caucasian. One hundred and sixty-four patients were seen in the Clinic between August 1976 and August 1977. Details of their original episode of visual impairment were recorded and enquiry made into any symptoms preceding this and into any illness since the episode of optic neuritis. The date of the first attack of optic neuritis, which was not always the attack which led to the patient's attendance at Moorfields, was obtained where possible from the hospital notes but in a minority of cases the patient's memory was relied upon. The period of follow-up was taken as the time from the onset of the original attack to the time of reassessment or in patients developing MS to the time of development of neurological episodes outside the visual system. A neurological examination was performed on all patients and 10 ml of peripheral blood was taken for HLA typing. Eighteen patients who failed to fulfil the above criteria were excluded. Using the criteria of McDonald and Halliday (1977) the remaining 146 patients were classified at reassessment as having developed clinically definite, early probable or latent MS (ON/MS) or as having had optic neuritis only (ON-only). Recurrent or bilateral optic neuritis was diagnosed only when there was a clear history of new visual symptoms not attributable to the initial lesion. Patients in whom abnormal physical signs were found in both eyes were classified according to their history. Patients with more than one episode of visual impairment but without other neurological symptoms or signs were classified as having optic neuritis only. Visual evoked potentials had been studied in some of the patients at the time of the initial presentation but the results were not used as a criterion for inclusion in this study. Auditory and spinal evoked potentials were subsequently recorded in a number of patients with clinical evidence of optic neuritis only and those with abnormalities characteristic of demyelination of brain-stem (Robinson and Rudge, 1977) or spinal cord (Small, Matthews and Small, 1978) were classified as latent MS even though the clinical signs were restricted to the visual pathways.
500
D. A. S. COMPSTON AND OTHERS
The assignment of the HLA-DRw antigens was made by the WHO Committee after this study was completed and the cells from only a few patients in this study were tested against antisera specific for HLA-DRw2. STATISTICS The statistical significance of the results was assessed using the \2 test- The relative risk (RR) of MS developing in one group of patients compared with another was calculated according to Svejgaard et al. (1975) using the formula RR = BT 101-positive ON/MS BT 101-negative ON/MS
BT 101-negative ON-only, BT 101-positive ON-only
_
number of cases developing MS between 0 and 6 months (number of cases entering study)—(half number not followed up for 6 months)
This fraction with ON/MS is subtracted from one to derive the fraction with optic neuritis only. The new fraction with optic neuritis only is calculated for successive intervals and multiplied by the optic neuritis only fraction for the preceding interval, to obtain the next point on the curve. RESULTS
Clinical Assessment One hundred and forty-six patients were reviewed and tissue typed at an interval of one month to twenty-three years after their initial episode of optic neuritis. The mean duration of follow-up was 47-3 months. The results of the clinical analysis are shown in Table 1. Fifty-eight patients (40 per cent) had developed MS (ON/MS); T A B L E 1. C L I N I C A L A N A L Y S I S
Total No. patients reassessed Exclusions, non-European Caucasians „ , symptoms developed outside Europe , episodes preceding optic neuritis „ , technical „ , aged > 50 years at onset
164 2 2 11 1 2 18
Total No. patients in study Optic neuritis developing multiple sclerosis (ON/MS) clinically definite early probable or latent Optic neuritis only (ON-only)
146 (100%) 58 (40%) 36 22 88 (60%)
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A value greater than one signifies an increased risk and a value less than one, a decreased risk. Since the results were inevitably based on a clinical assessment at different stages in each patient's illness and since some patients who at reassessment still had optic neuritis only might later develop MS, an actuarial analysis was made. In this method a prediction is made of the fraction of patients who would remain with optic neuritis only, if all patients had been followed for the same time. This prediction is made for different intervals and a curve drawn. Using the method of Barnes (1965): Fraction with ON/MS at the end of the first interval (0-6 months)
RISK FACTORS IN MULTIPLE SCLEROSIS
501
36 of these were clinically definite and 22 were early probable or latent cases (EPL). Six cases with electrophysiological evidence only of more than one neurological lesion were included in the EPL group. Eighty-eight patients (60 per cent) were classified as optic neuritis only.
TABLE 2. RESULTS OF TYPING FOR HLA ANTIGENS B7 AND BT ON-ONLY AND ON I MS P A T I E N T S
No. studied All patients Optic neuritis only Multiple sclerosis (ON/MS)
101 IN
Positive
B7 Negative
Positive
BT101 Negative
146
60(41%)
86(59%)
100(68%)
46(32%)
88 58
rv 133(38%).
55 (63%); 31 (53%)i
51(58%) 49 (84%)
37(42%) 9 (16%)
|27(47%)
[ _ l ! x 2 = 108; /> = N S ; R R = 1-45. |
] y 2 = 11-40; P
FACTORS INFLUENCING THE RISK OF MULTIPLE SCLEROSIS DEVELOPING IN PATIENTS WITH OPTIC NEURITIS by D. A. S. COMPSTON, J. R. BATCHELOR, C. J. EARL and W. I. MCDONALD
INTRODUCTION
THE clinical syndrome of optic or retrobulbar neuritis (ON) is easily recognized in the typical case. After the exclusion of specific causes there remains a sizeable group of patients in whom the aetiology can not be identified (McDonald, 1977). Some of this latter group develop multiple sclerosis (MS) but the fact that after lengthy follow-up some patients do not have further neurological episodes suggests that isolated optic neuritis is more than one disease. Optic Neuritis and Multiple Sclerosis The statistics which relate optic neuritis to MS are complex. Some facts are well established: approximately 50 per cent of MS patients have a clinical episode of optic neuritis at some time during the course of their disease (McAlpine, Compston and Lumsden, 1955). Many of the remainder have ophthalmoscopic evidence of damage to the optic nerve and there is electrophysiological evidence of past optic neuritis in 90 per cent of clinically definite MS cases (Halliday, McDonald and Mushin, 1973). All of Lumsden's (1970) 36 unselected necropsies on MS patients showed optic nerve demyelination. Except in Japanese studies optic neuritis is the presenting symptom in approximately 20 per cent of cases (Leibowitz and Alter, 1973). The risk of MS developing later in patients with isolated optic neuritis is however less certain: the published incidence varies between 85 per cent (Lynn, 1959) and 13 per cent (Kurland, Auth, Beebe, Kurtzke, Lessell, Nagler and Nefzger, 1963). Several factors may contribute to these differences. First, diagnostic criteria for MS and optic neuritis, and the mean length of follow-up, vary between different studies. Bradley and Whitty (1968) found that cases developing MS after optic neuritis had declared themselves within four years, whereas McAlpine, Lumsden and Acheson (1965) concluded 'The longer the period of observation the higher
Downloaded from http://brain.oxfordjournals.org/ by guest on June 9, 2016
(From the Mclndoe Memorial Research Unit, East Grinstead, Moorfields Eye Hospital and the Institute of Neurology, Queen Square)
496
D. A. S. COMPSTON AND OTHERS
Downloaded from http://brain.oxfordjournals.org/ by guest on June 9, 2016
will be the percentage of cases of retrobulbar neuritis which develop signs of MS'. Since therefore the rate at which patients develop MS is unpredictable a comparison of the mean duration of follow-up between studies may not be useful. Secondly, the methods of analysis vary in different investigations. In most, the proportion of cases developing MS has been determined on the basis of the subsequent course. However, Nikoskelainen and Riekkinen (1974) also included patients who, when first seen with optic neuritis, had disseminated neurological signs or a history of past neurological symptoms. In the most recent study from Belfast, Hutchinson (1976) predicted on the basis of an actuarial analysis that 78 per cent of patients presenting with optic neuritis will have developed MS after fifteen years. Finally, the lower proportion of cases of optic neuritis developing MS in all series reported from the United States, compared with studies from Europe, suggests that there may be real differences in the risk of developing MS and that some of these differences may have a geographical basis. There have been a number of attempts to identify factors which might help to determine the risk of MS developing in the individual patient. Taub and Rucker (1954) investigated the effect of age of onset and found that the risk was marginally increased in those over the age of 20 years, when compared with younger patients. The effect on prognosis of bilateral as opposed to unilateral attacks was studied by Hierons and Lyle (1959). They found no suggestion that bilateral involvement carried a greater risk, irrespective of whether the two eyes were affected simultaneously or sequentially. They did not study recurrent unilateral cases. A number of investigators have noted a slight increase in the attack rate of optic neuritis in the spring and early summer but this seasonal variation has not hitherto proved to be of prognostic value (Taub and Rucker, 1954; Bradley and Whitty, 1967; Hutchinson, 1976). Genetic predisposition to multiple sclerosis has not previously been investigated as a risk factor in patients with optic neuritis. The observation that the proportion of affected first degree relatives of MS patients is twenty times higher than expected (McAlpine et al, 1965) has led to attempts to identify markers of genetic susceptibility to the disease. Until recently such investigations have been unsuccessful. However, the recent discovery of an association between certain tissue types and MS raises the possibility that tissue typing, at the time of the first neurological episode, might be useful in identifying those patients likely to develop disseminated lesions later. We have explored this possibility in patients presenting with isolated optic neuritis. In order to understand our approach to the present investigation it will be helpful to review the current state of knowledge of the major histocompatibility system in man and its relationship to MS.
RISK FACTORS IN MULTIPLE SCLEROSIS
497
HLA and Multiple Sclerosis MS was originally shown to be associated with the presence of HLA-A3 and HLA-B7 (Jersild, Svejgaard and Fog, 1972) but the association is weak. It is now thought that these associations are secondary and that an allele at an adjacent locus confers susceptibility to the disease. In many genetic systems an association between particular alleles does not usually occur in randomly mating populations. However in the HLA system there is a tendency for certain alleles (for example, HLA-A3 and -B7) to occur together more frequently than would be expected by chance alone. The biological importance of this phenomenon, known as linkage disequilibrium, has been discussed by McDevitt and Bodmer (1974). In relation to MS, the practical problem is to distinguish between the locus which codes for the
Downloaded from http://brain.oxfordjournals.org/ by guest on June 9, 2016
The Human Leucocyte Antigen System (HLA) Tissue compatibility is now known to be genetically determined. As in all genetic systems it is the gene products—in this case the HLA antigens—which confer specificity. The HLA antigens are coded for by genes occurring at four sites or loci on the sixth chromosome. There is one locus each for the HLA-A, -B, -C and -D genes (Svejgaard, Hauge, Jersild, Platz, Ryder, Staub Nielson and Thomsen, 1975). There are many alternative gene forms or alleles for each locus. Since the cells of each individual have paired chromosomes they will express only two antigens coded for at each of these four loci. Other genes are found in the same region and attention has recently been concentrated on a group of antigens which are mainly expressed on peripheral blood B-lymphocytes. These antigens are of interest because the genes coding for them are thought to be analogous to genes in mice which are involved in the control of the immune response (Svejgaard et ai, 1975). The murine antigens have been called immune response associated (la) and the human, la-like, antigens. The HLA-A, -B and -C antigens are detected by serological tests on unfractionated peripheral blood lymphocytes (60-80 per cent T-lymphocytes) whereas the la-like antigens are detected by similar tests on purified peripheral blood B-lymphocytes. The detection of HLA-D antigens is more difficult and depends on techniques involving cellular interaction. The definition of some antigens is still provisional and these are identified by the suffix 'w', for example, HLA-Dw2. Recently it has been shown that the la-like and the HLA-Dw antigens are very closely related and may indeed be identical, despite the fact that they are detected by different techniques. Since the evidence is conflicting the WHO Committee on HLA nomenclature has decided to call the la-like antigens HLA-D Related w (HLA-DRw) antigens {Histocompatibility Testing, 1977). In addition to these internationally accepted antigens a number of individual laboratories have defined la-like antigens. Many of these are known to be equivalent to WHO-assigned HLA-DRw antigens, but in other cases, the relationship is still uncertain.
498
D. A. S. COMPSTON AND OTHERS
PATIENTS The patients in this study had all attended the Physicians' Clinic at Moorfields Eye Hospital, City Road or High Holborn, during the past twenty-three years. They were identified by reviewing all the accessible notes. All available patients in whom a clinical diagnosis of optic neuritis had been made and in whom there was no record of neurological symptoms preceding the episode of visual impairment or signs at the time of presentation were asked to reattend the Clinic. As in our previous investigations, optic neuritis was diagnosed in patients presenting with the rapid onset of visual loss, usually accompanied by ocular pain on movement, in whom there was a reduction in visual acuity, with a central field defect, either with or without a swollen disc (Earl and Martin, 1967; Gould, Bird, Leaver and McDonald, 1977). Patients were excluded if they had a retinal lesion or if there was evidence of a condition other than MS which might cause an optic nerve lesion—for example, gross paranasal sinus disease, blood pressure over 180/110 mmHg or hypertensive retinal vascular disease, diabetes, a history of amaurosis fugax, rheumatic valvular heart disease, a family history of optic nerve disease, heavy tobacco or alcohol consumption, dietary deficiency, Vitamin B12 deficiency, regular use of drugs known to cause optic atrophy, hypercholesterotemia, syphilis, long-standing visual loss from other causes, patients with a clinical picture suggestive of ischamic optic neuropathy (Boghen and Glazer, 1975), patients who were
Downloaded from http://brain.oxfordjournals.org/ by guest on June 9, 2016
allele responsible for susceptibility and the loci which code for alleles showing secondary associations due to linkage disequilibrium. The allele showing the highest association is the best candidate for the role of susceptibility gene. HLA-D antigens were therefore studied and Jersild, Hansen, Svejgaard, Fog, Thomsen and Dupont (1973) demonstrated a stronger association between MS and HLA-Dw2 (original local name Ld7a). The development of relatively convenient and reliable techniques for detecting HLA-DRw antigens has stimulated the search for associations between these antigens and MS. The disease has now been shown to be most closely associated with three locally defined la-like antigens —Ag7a (Winchester, Ebers, Fu, Espinosa, Zabriskie and Kunkel, 1975), B group 4 (Terasaki, Park, Opelz and Ting, 1976) and BT 101 (Compston, Batchelor and McDonald, 1976)—and also with HLA-DRw2 {Histocompatibility Testing, 1977). In our own series of 156 MS cases BT 101 was present in 79 per cent compared with a frequency of 35 per cent in 85 controls. These HLA-DRw antigen associations with MS have now been confirmed in patients of Northern European stock, in Europe, Australia and North America {Histocompatibility Testing, 1977). By contrast, in Jordanian Arabs (Kurdi, Ayesh, Abdallat, Maayta, McDonald, Compston and Batchelor, 1977) and in Italians {Histocompatibility Testing, 1977) MS has been found to associate with a specifically different allele, HLA-DRw4. The question we have tried to answer in this study is whether HLA typing provides a useful guide to the risk of development of MS. Arnason, Fuller, Lehrich and Wray (1974) showed that HLA-A3 was present in a higher proportion of patients with MS than in patients with optic neuritis who had not developed MS during follow-up. The present investigation was designed to assess the prognostic significance of the presence of the antigen BT 101. We also assessed the importance of recurrent or bilateral episodes and the season of onset of optic neuritis.
RISK FACTORS IN MULTIPLE SCLEROSIS
499
IMMUNOLOGY HLA typing was done using well validated antisera against the HLA-A, -B and -C gene products in both the National Institutes of Health and a local lymphocytotoxicity test (Batchelor, 1973). HLADRw typing was done on cell populations enriched for B-lymphocytes by first separating lymphocytes from peripheral blood, anticoagulated with edetic acid (EDTA) by centrifugation over a density gradient of Ficoll-Triosil (metrizoate sodium). The cells were then washed in 5 Mm EDTA and incubated with papain treated sheep red blood cells (SRBCs) at 4° C overnight to form E rosettes. The rosetted T-lymphocytes were separated from the non-rosetted B-lymphocytes, macrophages and monocytes by further centrifugation over Ficoll-Triosil. The 'non-rosetted' cells were harvested, washed and resuspended in McCoy's medium with 0-5 per cent foetal calf serum. This suspension contained 80-90 per cent B-lymphocytes as judged by the uptake of fluorescent labelled anti-immunoglobulin. T-lymphocytes from the same blood samples were prepared by lysing the SRBCs in the separated E rosettes with 0-85 per cent ammonium chloride, and then washing and resuspending the lymphocytes as described for the B-lymphocytes. This suspension contained 99 per cent T-lymphocytes as judged by 're-rosetting'. T and B enriched cell suspensions from the same peripheral blood sample were always tested in parallel in lymphocytotoxicity tests in which 1 /A of target cell suspension (4x10* cells/ml) was incubated with a similar volume of antiserum for one hour at 20° C. The cells were then re-incubated with 5 ftl rabbit complement for two hours. 0-4 per cent trypan blue was used to assay cell death. Antisera for HLADRw typing were absorbed with pooled platelets (10lo/ml) three times at 4° C to remove antibodies directed against HLA-A, -B or -C gene products and all sera used to identify HLA-DRw antigens were shown after absorption to react with B- but not T-lymphocytes from the same blood sample. The cells from all patients were tested against antisera defining many HLA-A, -B, -C and -DRw antigens but in this paper the results are given only for the antigens HLA-B7 and BT101. This la-like antigen is equivalent to HLA-DRw2 but also cross-reacts with HLA-DRw 1 and some HLA-DRw6 positive cells.
Downloaded from http://brain.oxfordjournals.org/ by guest on June 9, 2016
not aged between 10 and 50 years at the onset of symptoms and patients in whom the symptoms developed outside Europe, or who were not Caucasian. One hundred and sixty-four patients were seen in the Clinic between August 1976 and August 1977. Details of their original episode of visual impairment were recorded and enquiry made into any symptoms preceding this and into any illness since the episode of optic neuritis. The date of the first attack of optic neuritis, which was not always the attack which led to the patient's attendance at Moorfields, was obtained where possible from the hospital notes but in a minority of cases the patient's memory was relied upon. The period of follow-up was taken as the time from the onset of the original attack to the time of reassessment or in patients developing MS to the time of development of neurological episodes outside the visual system. A neurological examination was performed on all patients and 10 ml of peripheral blood was taken for HLA typing. Eighteen patients who failed to fulfil the above criteria were excluded. Using the criteria of McDonald and Halliday (1977) the remaining 146 patients were classified at reassessment as having developed clinically definite, early probable or latent MS (ON/MS) or as having had optic neuritis only (ON-only). Recurrent or bilateral optic neuritis was diagnosed only when there was a clear history of new visual symptoms not attributable to the initial lesion. Patients in whom abnormal physical signs were found in both eyes were classified according to their history. Patients with more than one episode of visual impairment but without other neurological symptoms or signs were classified as having optic neuritis only. Visual evoked potentials had been studied in some of the patients at the time of the initial presentation but the results were not used as a criterion for inclusion in this study. Auditory and spinal evoked potentials were subsequently recorded in a number of patients with clinical evidence of optic neuritis only and those with abnormalities characteristic of demyelination of brain-stem (Robinson and Rudge, 1977) or spinal cord (Small, Matthews and Small, 1978) were classified as latent MS even though the clinical signs were restricted to the visual pathways.
500
D. A. S. COMPSTON AND OTHERS
The assignment of the HLA-DRw antigens was made by the WHO Committee after this study was completed and the cells from only a few patients in this study were tested against antisera specific for HLA-DRw2. STATISTICS The statistical significance of the results was assessed using the \2 test- The relative risk (RR) of MS developing in one group of patients compared with another was calculated according to Svejgaard et al. (1975) using the formula RR = BT 101-positive ON/MS BT 101-negative ON/MS
BT 101-negative ON-only, BT 101-positive ON-only
_
number of cases developing MS between 0 and 6 months (number of cases entering study)—(half number not followed up for 6 months)
This fraction with ON/MS is subtracted from one to derive the fraction with optic neuritis only. The new fraction with optic neuritis only is calculated for successive intervals and multiplied by the optic neuritis only fraction for the preceding interval, to obtain the next point on the curve. RESULTS
Clinical Assessment One hundred and forty-six patients were reviewed and tissue typed at an interval of one month to twenty-three years after their initial episode of optic neuritis. The mean duration of follow-up was 47-3 months. The results of the clinical analysis are shown in Table 1. Fifty-eight patients (40 per cent) had developed MS (ON/MS); T A B L E 1. C L I N I C A L A N A L Y S I S
Total No. patients reassessed Exclusions, non-European Caucasians „ , symptoms developed outside Europe , episodes preceding optic neuritis „ , technical „ , aged > 50 years at onset
164 2 2 11 1 2 18
Total No. patients in study Optic neuritis developing multiple sclerosis (ON/MS) clinically definite early probable or latent Optic neuritis only (ON-only)
146 (100%) 58 (40%) 36 22 88 (60%)
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A value greater than one signifies an increased risk and a value less than one, a decreased risk. Since the results were inevitably based on a clinical assessment at different stages in each patient's illness and since some patients who at reassessment still had optic neuritis only might later develop MS, an actuarial analysis was made. In this method a prediction is made of the fraction of patients who would remain with optic neuritis only, if all patients had been followed for the same time. This prediction is made for different intervals and a curve drawn. Using the method of Barnes (1965): Fraction with ON/MS at the end of the first interval (0-6 months)
RISK FACTORS IN MULTIPLE SCLEROSIS
501
36 of these were clinically definite and 22 were early probable or latent cases (EPL). Six cases with electrophysiological evidence only of more than one neurological lesion were included in the EPL group. Eighty-eight patients (60 per cent) were classified as optic neuritis only.
TABLE 2. RESULTS OF TYPING FOR HLA ANTIGENS B7 AND BT ON-ONLY AND ON I MS P A T I E N T S
No. studied All patients Optic neuritis only Multiple sclerosis (ON/MS)
101 IN
Positive
B7 Negative
Positive
BT101 Negative
146
60(41%)
86(59%)
100(68%)
46(32%)
88 58
rv 133(38%).
55 (63%); 31 (53%)i
51(58%) 49 (84%)
37(42%) 9 (16%)
|27(47%)
[ _ l ! x 2 = 108; /> = N S ; R R = 1-45. |
] y 2 = 11-40; P
