:Acta . .Ndurochlrurglca
Acta Neurochir (Wien) (1992) 115:71-78
9 Springer-Verlag 1992 Printed in Austria
Problems Related to Dorsal Root Entry Zone Lesions Y. Kumagai, K. Shimoji, T. Honma 1, S. Uchiyama 1, B. Ishijima 2, T. Hokari 2, H. Fujioka, S. Fukuda, and E. Ohama 3, * Departments of Anesthesiology and 1Orthopedics, Niigata University School of Medicine, Niigata, 2Department of Neurosurgery, Tokyo Metropolitan Neurological Hospital, Tokyo, 3Department of Pathology, Brain Research Institute, Niigata University, Niigata, Japan
Summary Several clinical problems related to the dorsal root entry zone lesions (DREZLs) in 15 patients with chronic pain are presented and discussed in terms of ratings of pain relief following surgery, development of sensory or motor weakness and postmortem histologies. Subjective pain relief exceeding 70% was achieved at around 2 weeks after the operations in most patients (13/15), and then decreased in some to 30 from 70% in the follow-up observations. Our new "objective" pain relief score was tested in these patients. A significant positive correlation between subjective pain relief and our objective pain relief scale was found, but some discrepancies between them were also found during the follow-up. Sensory loss, motor weakness, paraesthesia and a new pain were found as complications in 12, 7, 4 and 6 patients, respectively. Postmortem histological findings of the spinal cord in two p~itients with systemic lupus erythematosus and uterine cancer, who received bilateral DREZLs twice and bilateral DREZLs plus commissural myelotomy, respectively, indicate that care should be taken to avoid extension of the coagulation beyond the dorsal horn. Keywords. Dorsal root entry zone (DREZ) lesion; pain; histology; objective pain relief score.
Introduction Dorsal root entry zone lesion ( D R E Z L ) , originally i n t r o d u c e d b y S i n d o u 17 a n d a p p l i e d e x t e n s i v e l y b y N a s h o l d e t al. 9-12 especially i n p a t i e n t s w i t h b r a c h i a l p l e x u s a v u l s i o n , h a s b e e n tested i n i n t r a c t a b l e p a i n s y n d r o m e s at several institutes, a n d g o o d clinical results h a v e so far b e e n a c c u m u l a t e d . E n c o u r a g e d b y these reports, were p e r f o r m e d D R E Z L o n 35 p a t i e n t s w i t h i n t r a c t a b l e c h r o n i c p a i n s y n d r o m e s , a n d the i n i t i a l results were r e p o r t e d elsewhere 5. D u r i n g the c o u r s e o f o b s e r v a t i o n s o n the effets o f the D R E Z L , we h a v e e n c o u n t e r e d several clinical p r o b -
* Present address: Brain Research Institute, Tottori University, Nishi-machi, Yonago 683, Japan.
lems r e l a t e d to the o p e r a t i o n s . P a r t i c u l a r l y , we frequently noted some dissociation between observer's a n d p a t i e n t ' s o w n scores for p a i n relief after t r e a t m e n t i n p a t i e n t s w i t h c h r o n i c i n t r a c t a b l e p a i n . W e therefore d e v e l o p e d a s i m p l e objective p a i n relief scale a n d c o m p a r e d it w i t h the p a t i e n t ' s subjective p a i n relief score. T h u s , i n the p r e s e n t a d d i t i o n a l 15 cases we focussed o u r i n t e r e s t o n the i n i t i a l a n d f o l l o w - u p effects estim a t e d f r o m the p o i n t s o f view o f the p a t i e n t ' s c o m p l a i n t s a n d o b s e r v e r ' s scores w i t h o t h e r p r o b l e m s rel a t e d to the D R E Z L .
Patients and Methods Fifteen patients included in this study were aged from 31 to 74 years (see Table 2). Six patients had a complete or partial brachial plexus avulsion, 5 had spinal cord trauma, 2 had causalgia caused by nerve trauma, and two others had pain related to systemic lupus erythematosns (SLE) and cancer. All these patients had previously been unsuccessfully treated with analgesic drugs, nerve blocks and epidural spinal cord stimulation. The DREZL was carried out under general anaesthesia with the patients in the prone position, using the radiofrequency coagulation method as described by Nashold etal. 1~ H. Laminectomy was performed to expose physiological dermatomal levels of the spinal cord related to the injury or pain. The lesions were made by thermocoagulation at approximately 50 mA for 5 seconds, spaced 1 2 mm apart along the DREZ at 26-188 points depending on the extent of the lesions on one or both sides of the spinal cord. The coagulation electrode, an insulated stainless steel wire with a tapered uninsulated tip 2 mm in length 150 gm in diameter was introduced into the intermediolateral sulcus, angled at 30 ~to the sagittal plane. An epidural stimulation device, consisting of an epidural electrode with a subcutaneous receiver, was also implanted during DREZL in 4 patients in whom epidural stimulation was demonstrated to be partially effective before the operation. We added a modified spinal commissural myelotomy (SCM) 3 in 5 patients (4 with spinal cord trauma and one with cancer pain) at the rostral limit of the DREZL 25-50 mm long at the termination
Y. Kumagai et al.: Problems Related to Dorsal Root Entry Zone Lesions
72
of the DREZL operation. Before the SCM the distance from the dorsal surface of the cord to that of vertebral body was measured by inserting a straight wire at the midline, and the distance (5-6 ram) to the center of the spinal cord was estimated by halving that to the vertebra. A similar coagulation electrode (150~tm in diameter, tapered to the uninsulated 2mm tip) was inserted to the center of the cord to coagulate along the midline at several points with the same current intensity as in the DREZL. The SCM was performed aiming
Table 1. Objective Evaluation Score of Pain Relief I ADL
II Drugs (analgesics, tranquilizer, local anaesthetics) III Mood
very much improved improved no change decreased
+2 +1 0 - 1
withdrawn reduced no change increased
+2 +1 0 - 1
brightened no change depressed
+1 0 - 1
to assure a complete blockade of pain pathways and also to test whether it prevents the development of a new pain which is frequently observed after the operation at the border zone of the DREZL. Assessment of pain was performed by two criteria, one by subjective complaints of the patient (pain relief scale) and the other by "objective" observation by four persons, i.e. two pain clinicians (main care-giver and his assistant), a pain clinic nurse, and a family person. The patients were instructed to evaluate their pain from zero to 100 % before and after the DREZL. As subjective pain relief was sometimes difficult to evaluate, we have also applied our new method of "objective" pain evaluation score, as demonstrated in Table 1. It consists of changes in (1) activities of daily life (ADL) (2) drugs and (3) patient mood. Means of values collected from each observer were calculated and rounded off for decimal fractions. We adopted this objective pain evaluation score when the patients were released from bed rest (more than 3-4 weeks).
Results
S u r g i c a l r e s u l t s i n 15 p a t i e n t s a r e s u m m a r i z e d
in
T a b l e 2. I n i t i a l l y (i.e., a b o u t 2 w e e k s a f t e r t h e D R E Z L ) complete subjective pain relief (100%) was achieved in 9 patients, and 50-90%
pain relief was obtained in
another 6 patients. However, subjective pain relief de+5: excellent, + 3 ~ +4: good, + 1 ~ +2: fair, 0: poor, - 3 ~ - 1: worse. Observers: (1) a pain clinic physician - main care-giver, (2) a pain clinic physician- assistant, (3) a pain clinic nurse, (4) a member of the patient's family.
c r e a s e d i n 13 p a t i e n t s i n t h e f o l l o w - u p p e r i o d . D e c r e a s e in subjective pain relief occurred within 2-3 months following DREZL
i n all s u b j e c t s , a n d t h e r e a f t e r t h e
degree of subjective pain remained unchanged.
Table 1 (continued) Objective pain relief
Observation (y.m.)
E** G G F G F G
Complications sensory loss or decrease
motor weakness
others
7y9m 6y4m 5y 4y3m 4y 5m ly6m
+ + + + + +
+ -
phantom limb altered
G F P E G
4y 3ylm 3yl Im 2y6m 2m
+ -
+ + -
E G
4y9m 3yl0m
+ +
+
F F
(5y) (ly)
+ +
+ +
new pain (died)
G
2m
+
+
(died)
** E excellent, G good, F fair, P poor.
new pain phantom limb altered new pain new pain (died) new pain new pain involuntary leg movements (transient)
73
Y. Kumagai etal.: Problems Related to Dorsal Root Entry Zone Lesions Table 2. Patient Characteristics and the Effects of D R E Z Lesions no.
Case age (yrs)
sex
Pain duration (yrs)
site
DREZL
SCM
r. arm 1, arm r. arm i. arm 1. arm 1. arm 1. arm
Cs-T I (26)* Cs-T~ (70) C4-T 1 (106) C5-C 8 (31) Cs-T 1 (38) C4-T 1 (61) C4-C s (87)
(B) Spinal cord trauma 7. 63 M 8. 60 M 9. 49 F 10. 38 M ti, 43 M
6 6 1 10 2
bilat, bilat, bilat, bilat, bitat,
L3-S 3 (46) L2-$5 (18) T12-L3 (29 T10-L3 (122) T1-S 3 (48)
4 3
1. foot r. leg
Ls-S 3 (38) LI-S 3 (50)
(D) SLE (systemic lupus erythematosus) 14. 31 F 11 32 F 12
bilat, trunk bilat, trunk
Ts-T 9 (180) T4-T9 (40)
(E) Cancer pain 15. 37
bilat, legs
L~-Ss (56)
F F
F
1
follow-up
-
80 80 100 100 100
80 30 30 0 30
-
90
30
-
90
70
legs legs legs thigh legs
+
m
+ +
m
-
-
+ + + +
+ -
m
m
+
Subjective pain relief (%) initial (2-3 weeks)
segment
(A) Brachial plexus avulsion 1. 43 M 25 2. 47 F 10 3. 74 M 3 4. 57 M 6 5. 49 M 17 6. 62 F 2 62 F 2
(C) Causalgia 12. 48 13. 35
ESD
100 70 I00 100 100
30 30 0 80 30
100 100
80 70
60 60
30 30
50
50
SCM: Spinal commissural myelotomy. ESD: Implantation of epidural stimulation device. * Number in parentheses represents points of" coagulation.
On the other hand, objective pain relief ranging from fair to excellent was demonstrated in all patients except one at follow-up. Although a positive correlation was found between subjective (x) and objective (y) pain relief scores (y = 0.046x + 1.001; correlation coefficient = 0.701, p < 0.01), some dissociation between them were observed in 6 patients (no. 2, 3, 4, 5, 7 and 13 in Table 2), of which four occurred in patients with brachial plexus avulsion. In two patients (No. 6 and 14) additional DREZL was performed in response to the patient's request, resulting in good and fair pain relief, respectively. Epidural stimulation devices are still used in two patients (No. 3 and 4), not used but remains implanted in one patient (No. 1), and terminated in one patient (No. 8) due to the death caused by rupture of an aneurysm. Phantom limb sensations observed before DREZL were changed following surgery in two patients. A slight motor weakness was observed in seven patients, assistance in walking was needed in one patient (No. 14)
who underwent bilateral DREZLs at thoracic levels. Sensory loss or weakness sometimes complicated with dysaesthesia at or below the level of the DREZL was found in 12 cases. A slight new pain in the border zone of the DREZL developed in 6 cases. No other major complications were found following the operation. In one patient (No. 12) with causalgia, severe oedema complicated with intractable pain in the left leg, unresponsive to permanent lumbar sympathetic block, disappeared dramatically within a week following the DREZL (Fig. 1). Three patients died of their original diseases during the follow-up (Table 2). Two patients (one with uterine cancer and one with SLE) were autopsied. Histologically, the spinal cord of the patient with uterine cancer, who also underwent spinal commissural myelotomy, demonstrated degeneration not only of the dorsal horn but also of the dorsal column at the level of the DREZLs (Fig. 2). In the spinal cord of the patient with SLE, there was also asymmetrical degeneration of the
74
Y. Kumagai etal.: Problems Related to Dorsal Root Entry Zone Lesions
Fig. 1. Disappearance of the leg oedema, which was not improved by lumbar sympathetic block, following the DREZL in a patient (no. 12) with major causalgia. A) Before the operation, B) a week after the operation
'.'.'..'..... :
'q)
:"}"7
c) L
R
B
Fig. 2. A) Transverse section through the 2nd lumbar segment of the spinal cord in the patient with uterine cancer (no. 15) who died two months after bilateral DREZLs at the L1-S3 levels plus commissural myelotomy at the L~ level. Note degeneration of the dorsal horns and dorsal columns, more marked on the right (R) side. Dorsal horns were relatively spared from degeneration in this section (Kliiver-Barrera stain, x 9.4). B) Schematic drawing of the section to show the degenerated area (dotted)
L
R
B
Fig. 3. A) Transverse section through the 4th cervical segment of the spinal cord in a patient with SLE (no. 14) who died one year after the second bilateral DREZLs at the T4-T 9 levels. Note the secondary degeneration of a part of the fasciculus gracilis and spinocerebellar tract as well as the corticospinal tract even at the level of C4 (KliiverBarrera stain, x 9.4). B) Schematic drawing of the section to show the degenerated area (dotted)
Y. Kumagai etal.: Problems Related to Dorsal Root Entry Zone Lesions
bilateral dorsolateral columns and spinocerebellar tracts. The secondary degeneration of a part of the fasciculus gracilis and spinocerebellar tract as well as the corticospinal tract were noted bilaterally above and below the level of the DREZLs (Fig. 3). Discussion
Our present and previous results 5 obtained so far in the DREZL have demonstrated that the technique is effective partially but not completely, and also that complications such as motor and sensory weakness as well as the development of a new pain should be kept in mind. Reviewing the literature, the best results of the DREZLs have been obtained in brachial plexus avulsion9-11, 16-20,21. Although good results were also achieved in other types of de-afferentation pain such as post herpetic neuralgia2' 13, 18, spinal cord trauma 2' 20 and post amputation syndrome5' 13, success rates seem to be variable and lower than those in plexus avulsion. However, the DREZLs also had a successful result in our patient with causalgia (No. 12) caused by sciatic nerve trauma. The DREZL has also been tried in non-de-afferentation pain with fair to good results 5' 13. Our patient with SLE had a causalgia-like pain accompanied by anhidrosis. Although the nature and cause of pain in this patient were not ascertained, the DREZL was performed because of severeness of complaints unresponsive to several kinds of nerve block and spinal epidural stimulation. The results of two operations were fair at the follow-up in this patient. Several problems arising from our experience with DREZL will be discussed in the following paragraphs.
Our Methods of the DREZLs As mentioned in the section on methods, we applied electrical currents of 50 mA for approximately 5 sec in our DREZL. However, the coagulation time was varied at every lesion point. We controlled the coagulation time by microscopic observation of the changes in the colour and fluidity of the cord surface surrounding the electrode and also by the "fixation" or stabilization of the electrode in the cord mass at the time of its withdrawal. These anatomical criteria for an appropriate coagulation intensity seemed to be more reliable for keeping the consistency of coagulation than setting the current intensity and time at a certain value, since the impedance of the cord tissue could differ at every DREZ. However, we often experienced difficulty in judgement of coagulation efficacy when the DREZ was
75
covered by increased vascular beds or connective tissue caused by trauma. Even when the temperature of the coagulation electrode is measured and adjusted, the degree of the lesion could be variable depending on the tissue impedance. Thus, judging from our clinical experiences, the determination of the ideal coagulation intensity for the DREZL may be very difficult. We used a smaller coagulation electrode (150 gm in diameter) as compared with Nashold's original electrode (0.018 inch in diameter) to minimize the lateral spread of the lesion. In fact, the neurological complications fell since Nashold used a new smaller thermistor-controlled electrode (0.25 mm in diameter) I~ Others have made a larger lesion2~ Recently, CO2 and argon lasers have also been used in the DREZLs 7' 13 and histological examination revealed that the laser produced smaller lesions than the radiofrequency electrode 1. The use of lasers may be a promising technique to control the lesion size. However, there is a lack of detailed neurophysiological and neuropathological information on the effect of laser on neuronal tissue 23. A syrinx formation in the central part of the cord of the cat was reported with use of the laser after a 1- to 4-week survival period 12.
Decrease of the Effect of the DREZL in the Follow-up Period We can not explain why high effectiveness of the DREZL, which was demonstrated in all subjects in our series, at around two weeks following the operation, decreased in the follow-up period. First, incompleteness of the lesions might be one of the causes. Indeed, there were decreases of subjective pain relief during the follow-up in the two cases (No. 4 and 9) in which the number of coagulation points were relatively fewer than in the other cases (Table 2). However, reviewing the relationships between the number of coagulation points along the DREZ and the degree of subjective pain relief in the follow-up periods, revealed no significant correlation. For instance, we carried out the coagulations as completely as possible in cases 3, 10 and 14, but decreases in the subjective pain relief were observed in all these patients during the follow-up period. On the other hand, although the lesions were thought not to be complete at the time of operation in cases 1 and 15, the effect of the operation remained unchanged in the follow-up. Second, the origin of pain in these patients could also be situated at other sites which might be unmasked by the destruction of the DREZ. Third, the surgical lesions could cause a new development of de-
76
Y. Kumagaietal.: Problems Related to Dorsal Root EntryZone Lesions
afferentation pain, since the rostral and caudal DREZs remain de-afferented by surgery. A sligh but persistent new type of pain, which developed in six patients, may support this thesis. The decrease in the effectiveness of DREZL during the folow-up has also been reported by several investigators5' 10, 15
Relationship Between the Patient's Complaints and Observer's Judgments Although the present data on our "objective" evaluation score of pain relief following the DREZLs have demonstrated that a significant positive correlation is found between subjective and objective pain relief scores, some dissociation between them is also noted in 6 individual patients. The results may indicate that pain relief scores should be evaluated by these two criteria individually in such chronic pain patients suffering for a long time. Thus, a simple objective evaluation score developed in our pain clinic (Table l) may help to assess more accurately the effect of pain treatment in a chronic pain state. All the 4 observers participating in the present study were instructed to rate the scores of pain relief following the DREZLs not by the patient's complaints but only by changes in their ADL, mood and drugs. The ADL of the patient (No. 15) with cancer pain became difficult to evaluate in the progress of her disease. Thus, changes in the amount of drugs taken and her mood were the main measures for objective evaluation of her pain in the terminal state. Problems related to medical insurance also seem to affect complaints in patients traumatized by car accidents in our series.
Effects of Commissural Myelotomy Several successful results have been reported with commissural myelotomy particularly in cancer pain. The level, depth and length of incision are variable among the authors, cervical to lumbosacral, 3-4mm to complete division and 25 mm to 5 cord segments, respectively2~ Early complete pain relief has been reported to be 67-100% with some recurrence. As we inserted the electrode up to the center of the cord, the electrical lesions should have involved the anterior and posterior commissures as well as the peri-central canal of the spinal cord 3' 20. We could not, however, evaluate the effects of our commissural myelotomy, separating these from those of DREZL, since two methods were applied at the same time in all 5 subjects.
Changes in Phantom Limb Sensation Origins of phantom limb sensation have been variously interpreted, i.e., peripheral, spinal or supraspinal phenomena 8, 22. Characteristics of the phantom limb sensations also changed in two patients in the present study. One patient (No. l) complained before the operation that he could not open his right hand, always a fist. He revealed after surgery that he now could open his right hand freely. Another patient (No. 6) reported that her left arm, which had been fixed to the left hypochondrial region, was "released" from her body to hang near the left-side of the waist. These changes in phantom limb sensations after the DREZL may suggest that the DREZ is one of the possible origins for the development of phantom limb sensation. Various types of phantom limb sensations experienced in patients with de-afferented limbs also suggest that cortical mechanisms are involved in the manifestation of such sensations8.
Sensory and Motor Weakness Sensory loss or decrease following the DREZL performed with thermocoagulation may be inevitable due to the surgical destruction of the dorsal horn 15'20. Motor weakness might be due to an extension of the radiofrequency lesions to motor tract area, to dorsal column15, 20, or to muscle-tendon reflex arc. Indeed, there were substantial extensions of the lesion to the dorsal and lateral column in the autopsy performed in a patient with SLE who underwent extensive bilateral DREZLs twice. Although this might be an extreme example, care should be taken in cases of bilateral DREZLs particularly at the thoracic level where the spinal cord forms a smaller mass. We have also pointed out previously the possibility for coagulation of cord surface vessels by the technique 5. For elimination of these complications microsurgical procedures 6' 17 19 C027 or argon 13 surgical lasers were used in some institutes. The microsurgical DREZ-tomy advocated by Sindou and his colleagues6' 17 19 might minimize the extension of lesions.
Appearance of a New Pain A slight new type of pain developing in 6 cases might be one of the problems encountered in the surgical methods for pain control. The characteristics of this pain appearing after the DREZL seemed similar to that of de-afferentation, accompanying paraesthesia or burning sensation 15'2o. Cervical or lumbar sympathetic
Y. Kumagai etal.: Problems Related to Dorsal Root Entry Zone Lesions b l o c k gave only p a r t i a l relief in 3 o f 5 p a t i e n t s tested. E p i d u r a l spinal c o r d s t i m u l a t i o n was also p a r t i a l l y effective in 4 o f 5 patients. W e have no effective count e r m e a s u r e for this c o m p l i c a t i o n at present. W e could n o t find a n y definite a d v a n t a g e o f the a d d i t i o n a l S C M in this r e g a r d to p r e v e n t this new p a i n at the b o r d e r zone o f the D R E Z L . M o r e clinical observations m i g h t be n e e d e d to define the c o m b i n e d S C M with the D R E Z L .
Histology Following Bilateral DREZLs and D R E Z L plus Commissural Myelotomy T h e p a t i e n t with S L E was o p e r a t e d on twice on b o t h sides to t h o r a c i c D R E Z at T 6 - T 9 a n d T r 9. I t is conceivable t h a t the chance o f the extension o f the lesion to the d o r s a l c o l u m n 15' 20 f r o m the D R E Z m a y increase with two o p e r a t i v e procedures. F u r t h e r , the d o r s a l h o r n o f the t h o r a c i c spinal c o r d is smaller t h a n t h a t o f the cervical or l u m b a r cord, which m a y also increase the chance o f d o r s a l c o l u m n d a m a g e caused by D R E Z L . I n the p a t i e n t with uterine cancer we a d d e d a c o m m i s s u r a l m y e l o t o m y at the r o s t r a l limit (L1) 5 0 r a m long. It m i g h t be inevitable t h a t m o r e m e c h a n i c a l d a m age to the d o r s a l c o l u m n occurs w h e n a d v a n c i n g the electrode to the p e r i c a n a l area. Thus, the d o r s a l c o l u m n d e g e n e r a t i o n d e m o n s t r a t e d in this p a t i e n t m i g h t m o s t l y be due to the c o m m i s s u r a l m y e l o t o m y r a t h e r t h a n the DREZL. T h e findings in these autopsies reveal t h a t m o r e a c c u r a t e p o s i t i o n i n g o f the c o a g u l a t i o n electrode is n e e d e d o r the alternative m e t h o d s such as laser 7' 13 or the m i c r o s u r g i c a l D R E Z t o m y 17 s h o u l d be considered. Besides these two p a t i e n t s with u n u s u a l l y extensive surgical lesions, we have no a u t o p s y cases d u r i n g the foll o w - u p after u n i l a t e r a l D R E Z L which was p e r f o r m e d in m o s t cases. O n l y three a u t o p s y r e p o r t s p u b l i s h e d to d a t e revealed t h a t D R E Z L s m a d e a 40-50 m A for 5 15 seconds d e s t r o y e d l a m i n a e I t h r o u g h IV o r VI with or w i t h o u t i m p i n g e m e n t in the white m a t t e r 4' 9, 14. A larger n u m b e r a n d m o r e detailed studies on the s p r e a d o f D R E Z L in r e l a t i o n to n e u r o l o g i c a l signs a n d s y m p toms are needed.
Acknowledgements Authors thank Dr. Martin D, Soko11 for kindly reviewing the manuscript.
77
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Correspondence and Reprints: Koki Shim@, M.D., Department of Anesthesiology, Niigata University School of Medicine, 1-757 Asahi-machi, Niigata 951, Japan.
Acta Neurochir (Wien) (1992) 115:71-78
9 Springer-Verlag 1992 Printed in Austria
Problems Related to Dorsal Root Entry Zone Lesions Y. Kumagai, K. Shimoji, T. Honma 1, S. Uchiyama 1, B. Ishijima 2, T. Hokari 2, H. Fujioka, S. Fukuda, and E. Ohama 3, * Departments of Anesthesiology and 1Orthopedics, Niigata University School of Medicine, Niigata, 2Department of Neurosurgery, Tokyo Metropolitan Neurological Hospital, Tokyo, 3Department of Pathology, Brain Research Institute, Niigata University, Niigata, Japan
Summary Several clinical problems related to the dorsal root entry zone lesions (DREZLs) in 15 patients with chronic pain are presented and discussed in terms of ratings of pain relief following surgery, development of sensory or motor weakness and postmortem histologies. Subjective pain relief exceeding 70% was achieved at around 2 weeks after the operations in most patients (13/15), and then decreased in some to 30 from 70% in the follow-up observations. Our new "objective" pain relief score was tested in these patients. A significant positive correlation between subjective pain relief and our objective pain relief scale was found, but some discrepancies between them were also found during the follow-up. Sensory loss, motor weakness, paraesthesia and a new pain were found as complications in 12, 7, 4 and 6 patients, respectively. Postmortem histological findings of the spinal cord in two p~itients with systemic lupus erythematosus and uterine cancer, who received bilateral DREZLs twice and bilateral DREZLs plus commissural myelotomy, respectively, indicate that care should be taken to avoid extension of the coagulation beyond the dorsal horn. Keywords. Dorsal root entry zone (DREZ) lesion; pain; histology; objective pain relief score.
Introduction Dorsal root entry zone lesion ( D R E Z L ) , originally i n t r o d u c e d b y S i n d o u 17 a n d a p p l i e d e x t e n s i v e l y b y N a s h o l d e t al. 9-12 especially i n p a t i e n t s w i t h b r a c h i a l p l e x u s a v u l s i o n , h a s b e e n tested i n i n t r a c t a b l e p a i n s y n d r o m e s at several institutes, a n d g o o d clinical results h a v e so far b e e n a c c u m u l a t e d . E n c o u r a g e d b y these reports, were p e r f o r m e d D R E Z L o n 35 p a t i e n t s w i t h i n t r a c t a b l e c h r o n i c p a i n s y n d r o m e s , a n d the i n i t i a l results were r e p o r t e d elsewhere 5. D u r i n g the c o u r s e o f o b s e r v a t i o n s o n the effets o f the D R E Z L , we h a v e e n c o u n t e r e d several clinical p r o b -
* Present address: Brain Research Institute, Tottori University, Nishi-machi, Yonago 683, Japan.
lems r e l a t e d to the o p e r a t i o n s . P a r t i c u l a r l y , we frequently noted some dissociation between observer's a n d p a t i e n t ' s o w n scores for p a i n relief after t r e a t m e n t i n p a t i e n t s w i t h c h r o n i c i n t r a c t a b l e p a i n . W e therefore d e v e l o p e d a s i m p l e objective p a i n relief scale a n d c o m p a r e d it w i t h the p a t i e n t ' s subjective p a i n relief score. T h u s , i n the p r e s e n t a d d i t i o n a l 15 cases we focussed o u r i n t e r e s t o n the i n i t i a l a n d f o l l o w - u p effects estim a t e d f r o m the p o i n t s o f view o f the p a t i e n t ' s c o m p l a i n t s a n d o b s e r v e r ' s scores w i t h o t h e r p r o b l e m s rel a t e d to the D R E Z L .
Patients and Methods Fifteen patients included in this study were aged from 31 to 74 years (see Table 2). Six patients had a complete or partial brachial plexus avulsion, 5 had spinal cord trauma, 2 had causalgia caused by nerve trauma, and two others had pain related to systemic lupus erythematosns (SLE) and cancer. All these patients had previously been unsuccessfully treated with analgesic drugs, nerve blocks and epidural spinal cord stimulation. The DREZL was carried out under general anaesthesia with the patients in the prone position, using the radiofrequency coagulation method as described by Nashold etal. 1~ H. Laminectomy was performed to expose physiological dermatomal levels of the spinal cord related to the injury or pain. The lesions were made by thermocoagulation at approximately 50 mA for 5 seconds, spaced 1 2 mm apart along the DREZ at 26-188 points depending on the extent of the lesions on one or both sides of the spinal cord. The coagulation electrode, an insulated stainless steel wire with a tapered uninsulated tip 2 mm in length 150 gm in diameter was introduced into the intermediolateral sulcus, angled at 30 ~to the sagittal plane. An epidural stimulation device, consisting of an epidural electrode with a subcutaneous receiver, was also implanted during DREZL in 4 patients in whom epidural stimulation was demonstrated to be partially effective before the operation. We added a modified spinal commissural myelotomy (SCM) 3 in 5 patients (4 with spinal cord trauma and one with cancer pain) at the rostral limit of the DREZL 25-50 mm long at the termination
Y. Kumagai et al.: Problems Related to Dorsal Root Entry Zone Lesions
72
of the DREZL operation. Before the SCM the distance from the dorsal surface of the cord to that of vertebral body was measured by inserting a straight wire at the midline, and the distance (5-6 ram) to the center of the spinal cord was estimated by halving that to the vertebra. A similar coagulation electrode (150~tm in diameter, tapered to the uninsulated 2mm tip) was inserted to the center of the cord to coagulate along the midline at several points with the same current intensity as in the DREZL. The SCM was performed aiming
Table 1. Objective Evaluation Score of Pain Relief I ADL
II Drugs (analgesics, tranquilizer, local anaesthetics) III Mood
very much improved improved no change decreased
+2 +1 0 - 1
withdrawn reduced no change increased
+2 +1 0 - 1
brightened no change depressed
+1 0 - 1
to assure a complete blockade of pain pathways and also to test whether it prevents the development of a new pain which is frequently observed after the operation at the border zone of the DREZL. Assessment of pain was performed by two criteria, one by subjective complaints of the patient (pain relief scale) and the other by "objective" observation by four persons, i.e. two pain clinicians (main care-giver and his assistant), a pain clinic nurse, and a family person. The patients were instructed to evaluate their pain from zero to 100 % before and after the DREZL. As subjective pain relief was sometimes difficult to evaluate, we have also applied our new method of "objective" pain evaluation score, as demonstrated in Table 1. It consists of changes in (1) activities of daily life (ADL) (2) drugs and (3) patient mood. Means of values collected from each observer were calculated and rounded off for decimal fractions. We adopted this objective pain evaluation score when the patients were released from bed rest (more than 3-4 weeks).
Results
S u r g i c a l r e s u l t s i n 15 p a t i e n t s a r e s u m m a r i z e d
in
T a b l e 2. I n i t i a l l y (i.e., a b o u t 2 w e e k s a f t e r t h e D R E Z L ) complete subjective pain relief (100%) was achieved in 9 patients, and 50-90%
pain relief was obtained in
another 6 patients. However, subjective pain relief de+5: excellent, + 3 ~ +4: good, + 1 ~ +2: fair, 0: poor, - 3 ~ - 1: worse. Observers: (1) a pain clinic physician - main care-giver, (2) a pain clinic physician- assistant, (3) a pain clinic nurse, (4) a member of the patient's family.
c r e a s e d i n 13 p a t i e n t s i n t h e f o l l o w - u p p e r i o d . D e c r e a s e in subjective pain relief occurred within 2-3 months following DREZL
i n all s u b j e c t s , a n d t h e r e a f t e r t h e
degree of subjective pain remained unchanged.
Table 1 (continued) Objective pain relief
Observation (y.m.)
E** G G F G F G
Complications sensory loss or decrease
motor weakness
others
7y9m 6y4m 5y 4y3m 4y 5m ly6m
+ + + + + +
+ -
phantom limb altered
G F P E G
4y 3ylm 3yl Im 2y6m 2m
+ -
+ + -
E G
4y9m 3yl0m
+ +
+
F F
(5y) (ly)
+ +
+ +
new pain (died)
G
2m
+
+
(died)
** E excellent, G good, F fair, P poor.
new pain phantom limb altered new pain new pain (died) new pain new pain involuntary leg movements (transient)
73
Y. Kumagai etal.: Problems Related to Dorsal Root Entry Zone Lesions Table 2. Patient Characteristics and the Effects of D R E Z Lesions no.
Case age (yrs)
sex
Pain duration (yrs)
site
DREZL
SCM
r. arm 1, arm r. arm i. arm 1. arm 1. arm 1. arm
Cs-T I (26)* Cs-T~ (70) C4-T 1 (106) C5-C 8 (31) Cs-T 1 (38) C4-T 1 (61) C4-C s (87)
(B) Spinal cord trauma 7. 63 M 8. 60 M 9. 49 F 10. 38 M ti, 43 M
6 6 1 10 2
bilat, bilat, bilat, bilat, bitat,
L3-S 3 (46) L2-$5 (18) T12-L3 (29 T10-L3 (122) T1-S 3 (48)
4 3
1. foot r. leg
Ls-S 3 (38) LI-S 3 (50)
(D) SLE (systemic lupus erythematosus) 14. 31 F 11 32 F 12
bilat, trunk bilat, trunk
Ts-T 9 (180) T4-T9 (40)
(E) Cancer pain 15. 37
bilat, legs
L~-Ss (56)
F F
F
1
follow-up
-
80 80 100 100 100
80 30 30 0 30
-
90
30
-
90
70
legs legs legs thigh legs
+
m
+ +
m
-
-
+ + + +
+ -
m
m
+
Subjective pain relief (%) initial (2-3 weeks)
segment
(A) Brachial plexus avulsion 1. 43 M 25 2. 47 F 10 3. 74 M 3 4. 57 M 6 5. 49 M 17 6. 62 F 2 62 F 2
(C) Causalgia 12. 48 13. 35
ESD
100 70 I00 100 100
30 30 0 80 30
100 100
80 70
60 60
30 30
50
50
SCM: Spinal commissural myelotomy. ESD: Implantation of epidural stimulation device. * Number in parentheses represents points of" coagulation.
On the other hand, objective pain relief ranging from fair to excellent was demonstrated in all patients except one at follow-up. Although a positive correlation was found between subjective (x) and objective (y) pain relief scores (y = 0.046x + 1.001; correlation coefficient = 0.701, p < 0.01), some dissociation between them were observed in 6 patients (no. 2, 3, 4, 5, 7 and 13 in Table 2), of which four occurred in patients with brachial plexus avulsion. In two patients (No. 6 and 14) additional DREZL was performed in response to the patient's request, resulting in good and fair pain relief, respectively. Epidural stimulation devices are still used in two patients (No. 3 and 4), not used but remains implanted in one patient (No. 1), and terminated in one patient (No. 8) due to the death caused by rupture of an aneurysm. Phantom limb sensations observed before DREZL were changed following surgery in two patients. A slight motor weakness was observed in seven patients, assistance in walking was needed in one patient (No. 14)
who underwent bilateral DREZLs at thoracic levels. Sensory loss or weakness sometimes complicated with dysaesthesia at or below the level of the DREZL was found in 12 cases. A slight new pain in the border zone of the DREZL developed in 6 cases. No other major complications were found following the operation. In one patient (No. 12) with causalgia, severe oedema complicated with intractable pain in the left leg, unresponsive to permanent lumbar sympathetic block, disappeared dramatically within a week following the DREZL (Fig. 1). Three patients died of their original diseases during the follow-up (Table 2). Two patients (one with uterine cancer and one with SLE) were autopsied. Histologically, the spinal cord of the patient with uterine cancer, who also underwent spinal commissural myelotomy, demonstrated degeneration not only of the dorsal horn but also of the dorsal column at the level of the DREZLs (Fig. 2). In the spinal cord of the patient with SLE, there was also asymmetrical degeneration of the
74
Y. Kumagai etal.: Problems Related to Dorsal Root Entry Zone Lesions
Fig. 1. Disappearance of the leg oedema, which was not improved by lumbar sympathetic block, following the DREZL in a patient (no. 12) with major causalgia. A) Before the operation, B) a week after the operation
'.'.'..'..... :
'q)
:"}"7
c) L
R
B
Fig. 2. A) Transverse section through the 2nd lumbar segment of the spinal cord in the patient with uterine cancer (no. 15) who died two months after bilateral DREZLs at the L1-S3 levels plus commissural myelotomy at the L~ level. Note degeneration of the dorsal horns and dorsal columns, more marked on the right (R) side. Dorsal horns were relatively spared from degeneration in this section (Kliiver-Barrera stain, x 9.4). B) Schematic drawing of the section to show the degenerated area (dotted)
L
R
B
Fig. 3. A) Transverse section through the 4th cervical segment of the spinal cord in a patient with SLE (no. 14) who died one year after the second bilateral DREZLs at the T4-T 9 levels. Note the secondary degeneration of a part of the fasciculus gracilis and spinocerebellar tract as well as the corticospinal tract even at the level of C4 (KliiverBarrera stain, x 9.4). B) Schematic drawing of the section to show the degenerated area (dotted)
Y. Kumagai etal.: Problems Related to Dorsal Root Entry Zone Lesions
bilateral dorsolateral columns and spinocerebellar tracts. The secondary degeneration of a part of the fasciculus gracilis and spinocerebellar tract as well as the corticospinal tract were noted bilaterally above and below the level of the DREZLs (Fig. 3). Discussion
Our present and previous results 5 obtained so far in the DREZL have demonstrated that the technique is effective partially but not completely, and also that complications such as motor and sensory weakness as well as the development of a new pain should be kept in mind. Reviewing the literature, the best results of the DREZLs have been obtained in brachial plexus avulsion9-11, 16-20,21. Although good results were also achieved in other types of de-afferentation pain such as post herpetic neuralgia2' 13, 18, spinal cord trauma 2' 20 and post amputation syndrome5' 13, success rates seem to be variable and lower than those in plexus avulsion. However, the DREZLs also had a successful result in our patient with causalgia (No. 12) caused by sciatic nerve trauma. The DREZL has also been tried in non-de-afferentation pain with fair to good results 5' 13. Our patient with SLE had a causalgia-like pain accompanied by anhidrosis. Although the nature and cause of pain in this patient were not ascertained, the DREZL was performed because of severeness of complaints unresponsive to several kinds of nerve block and spinal epidural stimulation. The results of two operations were fair at the follow-up in this patient. Several problems arising from our experience with DREZL will be discussed in the following paragraphs.
Our Methods of the DREZLs As mentioned in the section on methods, we applied electrical currents of 50 mA for approximately 5 sec in our DREZL. However, the coagulation time was varied at every lesion point. We controlled the coagulation time by microscopic observation of the changes in the colour and fluidity of the cord surface surrounding the electrode and also by the "fixation" or stabilization of the electrode in the cord mass at the time of its withdrawal. These anatomical criteria for an appropriate coagulation intensity seemed to be more reliable for keeping the consistency of coagulation than setting the current intensity and time at a certain value, since the impedance of the cord tissue could differ at every DREZ. However, we often experienced difficulty in judgement of coagulation efficacy when the DREZ was
75
covered by increased vascular beds or connective tissue caused by trauma. Even when the temperature of the coagulation electrode is measured and adjusted, the degree of the lesion could be variable depending on the tissue impedance. Thus, judging from our clinical experiences, the determination of the ideal coagulation intensity for the DREZL may be very difficult. We used a smaller coagulation electrode (150 gm in diameter) as compared with Nashold's original electrode (0.018 inch in diameter) to minimize the lateral spread of the lesion. In fact, the neurological complications fell since Nashold used a new smaller thermistor-controlled electrode (0.25 mm in diameter) I~ Others have made a larger lesion2~ Recently, CO2 and argon lasers have also been used in the DREZLs 7' 13 and histological examination revealed that the laser produced smaller lesions than the radiofrequency electrode 1. The use of lasers may be a promising technique to control the lesion size. However, there is a lack of detailed neurophysiological and neuropathological information on the effect of laser on neuronal tissue 23. A syrinx formation in the central part of the cord of the cat was reported with use of the laser after a 1- to 4-week survival period 12.
Decrease of the Effect of the DREZL in the Follow-up Period We can not explain why high effectiveness of the DREZL, which was demonstrated in all subjects in our series, at around two weeks following the operation, decreased in the follow-up period. First, incompleteness of the lesions might be one of the causes. Indeed, there were decreases of subjective pain relief during the follow-up in the two cases (No. 4 and 9) in which the number of coagulation points were relatively fewer than in the other cases (Table 2). However, reviewing the relationships between the number of coagulation points along the DREZ and the degree of subjective pain relief in the follow-up periods, revealed no significant correlation. For instance, we carried out the coagulations as completely as possible in cases 3, 10 and 14, but decreases in the subjective pain relief were observed in all these patients during the follow-up period. On the other hand, although the lesions were thought not to be complete at the time of operation in cases 1 and 15, the effect of the operation remained unchanged in the follow-up. Second, the origin of pain in these patients could also be situated at other sites which might be unmasked by the destruction of the DREZ. Third, the surgical lesions could cause a new development of de-
76
Y. Kumagaietal.: Problems Related to Dorsal Root EntryZone Lesions
afferentation pain, since the rostral and caudal DREZs remain de-afferented by surgery. A sligh but persistent new type of pain, which developed in six patients, may support this thesis. The decrease in the effectiveness of DREZL during the folow-up has also been reported by several investigators5' 10, 15
Relationship Between the Patient's Complaints and Observer's Judgments Although the present data on our "objective" evaluation score of pain relief following the DREZLs have demonstrated that a significant positive correlation is found between subjective and objective pain relief scores, some dissociation between them is also noted in 6 individual patients. The results may indicate that pain relief scores should be evaluated by these two criteria individually in such chronic pain patients suffering for a long time. Thus, a simple objective evaluation score developed in our pain clinic (Table l) may help to assess more accurately the effect of pain treatment in a chronic pain state. All the 4 observers participating in the present study were instructed to rate the scores of pain relief following the DREZLs not by the patient's complaints but only by changes in their ADL, mood and drugs. The ADL of the patient (No. 15) with cancer pain became difficult to evaluate in the progress of her disease. Thus, changes in the amount of drugs taken and her mood were the main measures for objective evaluation of her pain in the terminal state. Problems related to medical insurance also seem to affect complaints in patients traumatized by car accidents in our series.
Effects of Commissural Myelotomy Several successful results have been reported with commissural myelotomy particularly in cancer pain. The level, depth and length of incision are variable among the authors, cervical to lumbosacral, 3-4mm to complete division and 25 mm to 5 cord segments, respectively2~ Early complete pain relief has been reported to be 67-100% with some recurrence. As we inserted the electrode up to the center of the cord, the electrical lesions should have involved the anterior and posterior commissures as well as the peri-central canal of the spinal cord 3' 20. We could not, however, evaluate the effects of our commissural myelotomy, separating these from those of DREZL, since two methods were applied at the same time in all 5 subjects.
Changes in Phantom Limb Sensation Origins of phantom limb sensation have been variously interpreted, i.e., peripheral, spinal or supraspinal phenomena 8, 22. Characteristics of the phantom limb sensations also changed in two patients in the present study. One patient (No. l) complained before the operation that he could not open his right hand, always a fist. He revealed after surgery that he now could open his right hand freely. Another patient (No. 6) reported that her left arm, which had been fixed to the left hypochondrial region, was "released" from her body to hang near the left-side of the waist. These changes in phantom limb sensations after the DREZL may suggest that the DREZ is one of the possible origins for the development of phantom limb sensation. Various types of phantom limb sensations experienced in patients with de-afferented limbs also suggest that cortical mechanisms are involved in the manifestation of such sensations8.
Sensory and Motor Weakness Sensory loss or decrease following the DREZL performed with thermocoagulation may be inevitable due to the surgical destruction of the dorsal horn 15'20. Motor weakness might be due to an extension of the radiofrequency lesions to motor tract area, to dorsal column15, 20, or to muscle-tendon reflex arc. Indeed, there were substantial extensions of the lesion to the dorsal and lateral column in the autopsy performed in a patient with SLE who underwent extensive bilateral DREZLs twice. Although this might be an extreme example, care should be taken in cases of bilateral DREZLs particularly at the thoracic level where the spinal cord forms a smaller mass. We have also pointed out previously the possibility for coagulation of cord surface vessels by the technique 5. For elimination of these complications microsurgical procedures 6' 17 19 C027 or argon 13 surgical lasers were used in some institutes. The microsurgical DREZ-tomy advocated by Sindou and his colleagues6' 17 19 might minimize the extension of lesions.
Appearance of a New Pain A slight new type of pain developing in 6 cases might be one of the problems encountered in the surgical methods for pain control. The characteristics of this pain appearing after the DREZL seemed similar to that of de-afferentation, accompanying paraesthesia or burning sensation 15'2o. Cervical or lumbar sympathetic
Y. Kumagai etal.: Problems Related to Dorsal Root Entry Zone Lesions b l o c k gave only p a r t i a l relief in 3 o f 5 p a t i e n t s tested. E p i d u r a l spinal c o r d s t i m u l a t i o n was also p a r t i a l l y effective in 4 o f 5 patients. W e have no effective count e r m e a s u r e for this c o m p l i c a t i o n at present. W e could n o t find a n y definite a d v a n t a g e o f the a d d i t i o n a l S C M in this r e g a r d to p r e v e n t this new p a i n at the b o r d e r zone o f the D R E Z L . M o r e clinical observations m i g h t be n e e d e d to define the c o m b i n e d S C M with the D R E Z L .
Histology Following Bilateral DREZLs and D R E Z L plus Commissural Myelotomy T h e p a t i e n t with S L E was o p e r a t e d on twice on b o t h sides to t h o r a c i c D R E Z at T 6 - T 9 a n d T r 9. I t is conceivable t h a t the chance o f the extension o f the lesion to the d o r s a l c o l u m n 15' 20 f r o m the D R E Z m a y increase with two o p e r a t i v e procedures. F u r t h e r , the d o r s a l h o r n o f the t h o r a c i c spinal c o r d is smaller t h a n t h a t o f the cervical or l u m b a r cord, which m a y also increase the chance o f d o r s a l c o l u m n d a m a g e caused by D R E Z L . I n the p a t i e n t with uterine cancer we a d d e d a c o m m i s s u r a l m y e l o t o m y at the r o s t r a l limit (L1) 5 0 r a m long. It m i g h t be inevitable t h a t m o r e m e c h a n i c a l d a m age to the d o r s a l c o l u m n occurs w h e n a d v a n c i n g the electrode to the p e r i c a n a l area. Thus, the d o r s a l c o l u m n d e g e n e r a t i o n d e m o n s t r a t e d in this p a t i e n t m i g h t m o s t l y be due to the c o m m i s s u r a l m y e l o t o m y r a t h e r t h a n the DREZL. T h e findings in these autopsies reveal t h a t m o r e a c c u r a t e p o s i t i o n i n g o f the c o a g u l a t i o n electrode is n e e d e d o r the alternative m e t h o d s such as laser 7' 13 or the m i c r o s u r g i c a l D R E Z t o m y 17 s h o u l d be considered. Besides these two p a t i e n t s with u n u s u a l l y extensive surgical lesions, we have no a u t o p s y cases d u r i n g the foll o w - u p after u n i l a t e r a l D R E Z L which was p e r f o r m e d in m o s t cases. O n l y three a u t o p s y r e p o r t s p u b l i s h e d to d a t e revealed t h a t D R E Z L s m a d e a 40-50 m A for 5 15 seconds d e s t r o y e d l a m i n a e I t h r o u g h IV o r VI with or w i t h o u t i m p i n g e m e n t in the white m a t t e r 4' 9, 14. A larger n u m b e r a n d m o r e detailed studies on the s p r e a d o f D R E Z L in r e l a t i o n to n e u r o l o g i c a l signs a n d s y m p toms are needed.
Acknowledgements Authors thank Dr. Martin D, Soko11 for kindly reviewing the manuscript.
77
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Correspondence and Reprints: Koki Shim@, M.D., Department of Anesthesiology, Niigata University School of Medicine, 1-757 Asahi-machi, Niigata 951, Japan.
