azathioprine in myasthenia gravis

Journal of the Neurological Sciences, 1982, 57:357-368

357

Elsevier BiomedicalPress

T I M E C O U R S E OF I M P R O V E D N E U R O M U S C U L A R F U N C T I O N FOLLOWING PLASMA EXCHANGE ALONE AND PLASMA EXCHANGE W I T H P R E D N I S O N E / A Z A T H I O P R I N E IN M Y A S T H E N I A GRAVIS

H.S.

MILNER-BROWN and ROBERT G. MILLER

Neurology/Neuromuscular Research, Children's Hospital of San Francisco, San Francisco, CA (U.S.A.)

(Received 5 May, 1982) (Revised, received25 June, 1982) (Accepted 29 June, 1982)

SUMMARY Ten patients with myasthenia gravis (MG) were treated with weekly plasma exchange (PE) in combination with prednisone and azathioprine; 4 of the patients were treated with 3-6 PE alone, before instituting prednisone/azathioprine. Four clinico-physiological parameters of neuromuscular function as well as the antiacetylcholine receptor antibody (anti-AChRAb) titers were measured 1-3 times per week. Evidence of improved neuromuscular function (NMF) was based on: (1) reduced ~ decrement of the maximum muscle compound potential following 2/s supramaximal nerve stimulation; (2) increased maximum force; (3) increased outstretched arm time, and (4) increased vital capacity. An early improvement in N M F occurred within the first 2 weeks (sometimes as early as 1-2 days), which was quantitatively comparable in patients treated with PE alone and PE plus prednisone/ azathioprine. This early improvement reached a plateau, and was subsequently maintained for 3 4 weeks, followed by a later substantial improvement after 8-12 weeks of combined PE plus prednisone/azathioprine.

INTRODUCTION The most important clinical feature of myasthenia gravis (MG) is weakness and fatigability of skeletal muscles. A reduction in acetylcholine receptors is involved

This work was supported by the Muscular Dystrophy Association of America. Address for correspondence and reprint requests: Dr. H.S. Milner-Brown, Neurology/Neuromuscular Research (OPR-504), Children's Hospital of San Francisco, 3700 California Street, San Francisco, CA 94119, U.S.A. 0022-510X/82/0000-0000/$02.75 © 1982 Elsevier Biomedical Press

358 in the pathogenesis, and there are pathogenic anti-acetylcholine receptor antibodies (anti-AChRAb) in the serum of 90'~ of MG patients. (Aharonov et al. 1975: Appel et al. 1975; Bender et al. 1975; Engel et al. 1977: Lindstrom 1978: lto et al. 1978; Lindstrom et al. 1976, 1978; Vincent and Newsom-Davis 1980: Drachman et al. 1980). The possibility that the removal or reduction of antibodies would be therapeutic has been the rationale for using plasma exchange (plasmapheresis) to treat myasthenia gravis. In the past few years, plasma exchange, in conjunction with immunosuppressive drugs, has been used to treat MG with varying success. (Pinching et al. 1976; Behan et al. 1979; Dau et al. 1977, 1979; Denys et al. 1979, Newsom-Davis et al. 1978, 1979a,b; Arrigo et al. 1979; Lisak et al. 1979; Campbell et al. 1980; Dau 1980; Kornfeld et al. 1981). As a result, three relevant questions have been asked about this method of treatment: (1) Does plasma exchange directly improve neuromuscular function': (2) If so~ what is the time course of the improvement in neuromuscular (NM) function? (3) What is the time course of the improvement in NM function following treatment with plasma exchange in conjunction with prednisone and azathioprine and how does it differ from plasma exchange alone? In order to find answers to these questions, 4 clinico-physiological parameters of NM function, as well as the anti-AChRAb titer, were measured 2 or 3 times per week from 6 patients and once every 1 or 2 weeks from 4 other patients, all undergoing weekly plasma exchanges. This report provides data pertaining to, and some answers to, these questions. METHODS The 4 clinico-physiological parameters were: (1) ~o decrement of the maximum evoked potential recorded from the first dorsal interosseus and/or deltoid muscle using 2/s nerve stimulation; (2) Maximum force; (3) Outstretched arm time, and (4) Vital capacity, and in later studies, peak expiratory flow. Ulnar nerve stimulation

The patient was comfortably seated, with the right arm resting on a board on which a force transducer (Statham UC3), a hand stabilizer, and arm straps were mounted. The index finger was held in a metal ring attached to the transducer, at the proximal interphalangeal joint, and the thumb stabilized at an abduction angle of approximately 90 degrees. The arm was strapped to the board at the wrist and forearm. Surface electrodes were firmly taped to the ulnar nerve at the wrist for stimulation, and another pair of surface electrodes taped to the belly of the first dorsal interosseus (FDI) and close to the proximal interphalangeal joint, for recording the evoked muscle potentials. Conducting jelly was put on both the st:imulating and recording disc electrodes. A Thermistor thermometer probe was taped to the hand and covered with gauze sponges to partially shield it f r o m the direct heating effect of the lamp. The hand was heated with a lamp until a stable skin temperature of 38°C was attained. Six supramaximal stimuli of 0.1 ms duration and 2/s frequency were applied to the ulnar nerve and the evoked poten-

359 tials from the FDI recorded on a photosensitive paper (Kodak Linagraph 1895). The amplitude of the first (M1) and fifth (M5) potentials were measured, and the MI-M5 ~o decrement M ~ x 100 calculated. The procedure was repeated twice at 3-min intervals, and the average decrement calculated was used in the graph.

Brachial plexus stimulation The brachial plexus was stimulated (0.5 ms duration, 2/s frequency) by taping the stimulating electrode to the neck, the cathode being 6-7 cm vertically below the lobule of the pinna. The electrode was further stabilized with a Velcro strap around the neck. This arrangement ensured a stable stimulus location and reproducible evoked potentials recorded from the belly of the deltoid muscle. The protocol was the same as described for the ulnar nerve. Maximum force The maximum force exerted by abduction of the index finger against the force transducer at the proximal interphalangeal joint was measured with a calibrated digital multimeter. The maximum force (MF) was computed from the average of 3 maximum voluntary contractions. Arm time The patient was asked to extend the arm and hold it outstretched in a horizontal position for as long as possible, until the arm dropped due to fatigue. The duration of the outstretched position was the arm time. Vital capacity The vital capacity (VC) was measured 3 times with a spirometer and the best value was plotted. Plasma exchange The technical details of the procedure have been described elsewhere (Menke and Dau 1979). Plasmapheresis (plasma exchange) was performed using a celltrifuge continuous-flow blood-cell separator (American Instrument Co.). The volume of each exchange was 5~o BW (4 liters), and this was replaced by 2.5 1 of 5 ~ purified protein fraction (Plasmanate, Cutter Labs, Inc.), 1 1 Dextran-75 in 0.9~o NaC1 (Gentran, Travenol Labs, Inc.), and 0.5 1 of lactated Ringer's solution. Patient testing Six patients were tested before each plasma exchange, as well as 1 day, 4 and/or 7 days after the exchange. Four patients were tested less frequently, between 1 and 4 times per month. Testing was done at approximately the same time for each patient, 8 12 h after his last medication. Table 1 is a summary of the clinical data of the 10 patients.

360 TABLE l CLINICAL DATA OF 10 PATIENTS WITH MYASTHENIA GRAVIS Patients

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

1.B. J.C. V.V. B.J.C. J.V. K.L. E.M. B.S. H.S. K.N.

Age (yr)

52 22 45 54 38 41 48 25 60 65

Sex

M M M F F F M M F F

Duration Osserman of illness classifi(yr) cation

3 9 1 0.5 0.5 23 7 4 2 2

IV IV liB III liB liB IV IV IV liB

Thymus

No thymoma No thymoma Thymoma Intact Intact Intact Thymoma Thymoma Thymoma Intact

Time since thymectomy

Pre-plasma exchange medication (mg q.d.)

(yr) :~

Pyr.

Pred.

0.5 6 0.8

480 1680 300 0 0 720 600 480 600 180

0 0 0 0 0 0 100 35 30 0

4 4 Post PE

a Time between thymectomy and 1st PE. Pyr =pyridostigmine; Pred = prednisone; Post PE = patient H.S. underwent thymectomy after PE treatment.

Anti-acetylcholine receptor antibody titer The anti-AChRAb titer was measured by an immunoprecipitation assay. (Lindstrom et al. 1976; Newsom-Davis et al. 1978). The antigen used was "Triton"extracted human AChR obtained from amputated leg muscle, labeled with [~25I]alpha-bungarotoxin. Titers were expressed as nmol of alpha-bungarotoxinbinding sites precipitated per liter of serum. Patient 1 (I.B.) Fig. 1 Is a 52-year-old man with a 2-year history of myasthenia gravis. His symptoms included limb weakness and fatigability, as well as dysphagia, dysarthria, diplopia, ptosis and dyspnea. He underwent thymectomy (no thymoma) I I/2 years after diagnosis. The anti-AChRAb titer was elevated (50 nM/IL and previous medications were pyridostigmine (75 mg every 3 hJ and ephedrine (50 mg twice a dayL This patient underwent 6 plasma exchanges before azathioprine (250 mg daily) and prednisone (60 mg daily) were initiated. Patient 2 (J.C.) Is a 22-year-old man with a 9-year history of myasthenia gravls. He had limb weakness and fatigability in addition to ptosis, diplopia, dysarthria and dysphagia. He underwent thymectomy (no thymoma) 3 years after diagnosis and was treated with prednisone for 4 years (between the 3rd and 7th year of MG). Prior to and during plasma exchange he was taking 240 mg pyridostigmine every 3 h. After the 3rd plasma exchange, prednisone (60 mg daily) and azathioprine (240 mg daily) were initiated. Comment: His triphasic time course of improvement was: (i) an early improvement after the 2nd PE: (ii) worsening 4 days after the institution of prednisone/azathiopnne and a return to early improved function, and (iii) a later phase o f improvement after 8 weeks of concomitant immunosuppressive drugs. Patient 3 (V.V.) Fig. 2 A 45-year-old man who had episodes of dyspnea and generalized myasthenic weakness beginning at age 44. Following the surgical removal of a thymoma, he did well for several months without

361

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601

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601

501

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4 ~ PLASMA Z:~CH~U~GE 21

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49

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Fig. 1. Patient 1 (I.B.). A: Anti-acetylcholine receptor antibody titer (Ab) and % decrement of the maximum compound potentials recorded from the deltoid muscle (circles) and first dorsal interosseus (FDI) (squares), following supramaximal nerve stimulation at 2/s. B: Outstretched arm time (AT) and peak expiratory flow. The arrow indicated when prednisone and azathioprine were initiated, i.e., 3 days after the 6th PE. Note: (1) The most significant improvement in neuromuscular function occurred after the first 2 PE; between 3 PE and 6 PE there was no further improvement. (2) There was a significant decrease in AT and a slight increase in % dec 5 days after the initiation of prednisone/azathioprine. (3) Significant improvement of all parameters after 10 PE plus 4 weeks of coincident prednisone/ azathioprine.

medication. He subsequently worsened and developed ptosis, diplopia, dysarthria, dysphagia and difficulty with mastication. He was treated with pyridostigmine (60 mg every 4 h) plus 180 mg slow release pyridostigmine at bedtime, for 5 months, but continued to worsen. After 2 weekly plasma exchanges, prednisone (60 mg daily) and azathioprine (200 mg daily) were initiated. Patient 4 (B.J.C.)

A 54-year-old woman with a 6-month history of progressive severe bulbar and generalized myasthenia gravis treated with 2 plasma exchanges in 2 weeks before prednisone (100 mg/day) was instituted. After the 7th plasma exchange, azathioprine (125 mg daily) was initiated, and prednisone dosage reduced to 60 mg per day. She was the only patient who did not improve after 2 PE alone.

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Fig. 2. Patient 3 (V.V.). A : Anti-acetylcholine receptor antibody titer (Ab) a n d ",, decrement of the M C P recorded from the deltoid muscle following supramaximal stimulation o ( t h e brachial plexus at 2/s. B: Outstretched arm time (AT) and vital capacity (VC). The arrow indicates when prednisone/azathiopr ne ~erc initiated - - 7 days after the second PE.

363 Patient 5 (J.V.)

A 38-year-old woman with a 5-month history of weakness and easy fatigability. Her symptoms included diplopia, bilateral ptosis, dysarthria, dysphagia and fatigability of the muscles of mastication and of the limbs. There was moderate weakness of the face, tongue, neck flexors and limbs, as well as the extra-ocular muscles. Results of electrodiagnostic tests and improvement after edrophonium were typical for myasthenia gravis, although this patient had no elevation of anti-AChRAb titer. Azathioprine (200 mg daily) and prednisone (60 mg daily) were instituted after the first PE; she had previously tried prednisone alone for one month with no improvement. Comment: This patient was tested 3 times per week and her data showed that, in general, the least decrement (i.e., "optimum" neuromuscular transmission) was recorded 7 days after each PE; however, on 2 occasions (lst and 8th PE) the decrement was minimum after 4 days. Although this may just reflect random fluctuations of the decrement, the similar fluctuations of both the arm time and maximum force would suggest that after each exchange, several days may be required in order to achieve an optimum effect. [Kornfeld et al. (1981) reported that 4 MG patients who did not respond to PE "were treated much more intensively": 12 21 l of plasma were exchanged in 3 weeks, at 2-day intervals.] Patient 6 (K.L.)

A 41-year-old woman with a 23-year history of myasthenia gravis. Her symptoms included diplopia, dysphagia and dysarthria. There was weakness and fatigability of all limb muscles. The patient underwent 8 weekly plasma exchanges. Her only previous treatment with pyridostigmine (120 mg 6 times per day) and neostigmine (30 mg 6 times per day) was maintained. After the first plasma exchange, azathioprine (200 mg daily) and prednisone (60 mg daily) were initiated. Patient 7 (E.M.) Fig. 3

A 48-year-old man with a 7-year history of generalized MG. His symptoms included diplopia, ptosis, dysarthria, dysphagia and fatigability of the muscles of mastication and the limbs. He had previously been treated with pyridostigmine (60 mg every 3h) plus 180 mg slow release pyridostigmine at bedtime, and prednisone (30 mg daily). Patient 8 (B.S.)

A 25-year-old man who developed generalized myasthenia weakness at age 21. He underwent thymectomy (no thymoma), became nearly asymptomatic postoperatively, but began to worsen after a few months. He was treated with pyridostigmine (60 mg every 3 h), plus 180 mg slow release pyridostigmine at bedtime, and 70 mg prednisone on alternate days. Recently, worsening began when prednisone was tapered to 20 mg on alternate days. His symptoms, which included dyspnea, dysphagia and limb fatigability, prevented him from working as a carpenter. He was being treated with prednisone (60 mg daily) at the first exchange, and azathioprine (200 mg daily) was started one week after the second plasma exchange. Patient 9 (H.S.)

A 57-year-old woman with a 2-year history of MG. Her symptoms included generalized limb weakness, as well as ptosis, dysphagia and dysarthria. She had in the past been treated with azathioprine, prednisone and pyridostigmine. After the first exchange, azathioprine, 150 mg daily, and prednisone, 60 mg daily, were initiated, and pyridostigmine maintained at 180 mg every 4 h. Patient 10 (K.N.)

A 65-year-old woman, whose initial symptoms of diplopia, ptosis, fatigue and generalized muscle weakness occurred at age 63. She responded well to pyridostigmine (60 mg 3 times per day) for one year. Pyridostigmine dosage was reduced to 30 mg 3 times per day, and 2 months later, she worsened, and developed dysarthria and dysphagia. Prednisone (60 mg daily) was initiated, after the first exchange, azathioprine, 175 mg daily after the third PE, and pyridostigmine increased to 60 mg every 4 h. After I0 weekly plasma exchanges in combination with prednisone and azathioprine, the 65-yearold woman, who could previously barely raise her arm, held her arm outstretched for 7 minutes.

364 PATIENT: 7

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Fig. 3. Patient 7 (E.M.)..4: Anti-AChRAb titer and % decrement of maximum compound potential recorded from the deltoid muscle, following supramaximal stimulation of the brachial plexus at 2/s, B: Arm time and vital capacity. Evidence of improved neuromuscular function after the first PE were : oj ~o decrement 24 -*6, arm time 1.25 --,4 min, vital capacity 2.1 -~ 3.1 I: and anti-AChRAb titer 310 -* 190 nM/l.

DISCUSSION

The purpose of this study was to answer relevant questions regarding the effect of plasma exchange alone and in combination with immunosuppressive drug therapy in the management of myasthenia gravis. The first two questions were whether plasma exchange alone could improve neuromuscular function, and if so. over what time course. The third question was, "Is the time course of the response to plasma exchange combined with prednisone and azathioprine different from PE alone?" Table 2, which is a summary of the results, and answers pertaining to the above questions, will provide the bases for this discussion. The time course of the response from the onset of treatment generally followed a triphasic pattern, irrespective of when prednisone and azathioprine were instituted. Phase 1 was an "early improvement" in neuromuscular function: during Phase 2.

365 TABLE 2 S U M M A R Y OF T I M E C O U R S E OF I M P R O V E M E N T IN NM F U N C T I O N F O L L O W I N G PLASMA E X C H A N G E PLUS P R E D N I S O N E / A Z A T H I O P R I N E

Patients

Phase 1

less than 2 wks.early improvement 1. I.B.

2. 3. 4. 5. 6. 7. 8. 9. 10.

J.C. V.V. B.J.C. J.V. K.L. E.M. B.S. H.S. K.N.

+

+ + + + + + + +

Phase 2 (2-6 wks.)

Phase 3

6-12 wks. late improvement

_a

PE alone

PE plus pred/aza

_a 0 + 0 0 0 0 0 +

+ all 10 patients

+ = improvement in NM function; - = no improvement in NM function; 0 = no change in NM function. a Transient worsening after prednisone was initiated, followed by a gradual return to early improvement attained in Phase 1.

either the level of improvement was maintained without any additional improvement or there was worsening followed by a gradual return to the level of the early improvement; Phase 3, a later significant improvement occurred. With the exception of Patient 4 (B.J.C.), all patients showed an early improvement in neuromuscular function based on (i) the reduction in the percentage decrement following 2/s nerve stimulation; (ii) increased maximum force; (iii) increased vital capacity, and (iv) increased outstretched arm time. This early improvement occurred within 1 week after the first plasma exchange whether or not patienls were taking prednisone and azathioprine. The improvement documented in Patients 1, 2 and 3, who were treated with 3-6 plasma exchanges before instituting prednisone and azathioprine, was quantitatively comparable to that of the 6 patients treated with immunosuppressive drugs from the time of the first plasma exchange. These results as well as the published observations of the relatively slower action of prednisone and azathioprine (Hertel et al. 1979; Reuther et al. 1979), suggest that the early improvement in neuromuscular function was predominantly the effect of plasma exchange. The first two plasma exchanges produced the most significant (and sometimes dramatic) improvement in neuromuscular function within 7-14 days. The major reduction in anti-AChR antibody titer, the most significant increase in vital capacity, some increase in arm time, as well as the major reduction in the percentage decrement recorded from the first dorsal interosseus muscle (but not the deltoid), occurred during this period. Subsequent exchanges after the first few may not produce additional significant improvement in neuromuscular function (NMF);

366 however, they may help to maintain the early improvement. This was clearly seen in I.B. who reached a plateau of N M F after 3 weeks of PE alone (Fig: 1). In Patient 4 (B.J.C.), no response was observed until after prednisone and azathioprine were added. Two aspects of this patient were unusual: first, she was the weakest patient in the series, and second, no elevation of AChRAb was tbund in the serum. Following the early improvement, most patients went through a second phase lasting about 3-4 weeks, in which there was no further improvement in neuromuscular function, but the level of improvement was maintained. Patients 1 and 2 (I.B. and J.C.) worsened within 1 week after prednisone and azathioprine were instituted, and did not regain the early improved function until after 3 5 weeks. Early worsening after the initiation of high-dose prednisone has been previously reported (Brunner et al. 1972; Mann et al. 1976; Patten 1978). After the first few exchanges, these two patients also had improved neuromuscular function and the subsequent worsening following institution of high-dose prednisone was well tolerated. Thus, judicious use of plasma exchange may be the best strategy for alleviating the worsening of N M F associated with prednisone, especially in severely weak patients. In the 3rd phase, there was a significant decrease in the decrement from the deltoid, a substantial increase in arm time (Patient I.B. improved from 20 s to 10 min), a general increase in muscle strength, and a stable vital capacity. During the latter part of this phase, prednisone and pyridostigmine doses were reduced. Our conclusions are as follows: (1) Plasma exchanges alone can improve the condition of some patients with myasthenia gravis. (2) The early improvement resulting from the first few exchanges minimizes the impact of the early inhibitory effect ofprednisone. (3) The improvement in neuromuscular function resulting from plasma exchange alone may reach an early plateau, and additional plasma exchanges may only serve to keep antibody titers low and maintain function. To obtain further improvement immunosuppressive drug therapy is required. Thus, increased experience with plasma exchange had demonstrated its efficacy as well as its limitations. To determine the most effective utilization of this therapeutic modality, a multi-center controlled clinical study of immunosuppressive drugs and plasma exchange should be done. ACKNOWLEDGEMENTS The AChRAb titers were determined by Paul Morand. We also acknowledge the contribution of Sheryl Stuart in the d a t a collection, Ann Batmale for the illustrations and Mary DeLucco for typing the manuscript. REFERENCES Aharonov, A., O. Abramsky, R. Tarrab-Hazdai and S. Fuchs (1975) Humoral antibodies to acetylcholine receptor in patients with myastheniagravis, Lancet, ii: 340-342. Appel, S. H., P. E. Almon and N. Levy (1975) Acetylcholinereceptor antibodies in myastheniagravis, N. Engl. J. Med., 293: 760-761.

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368 Patten, B.M. (1978) Myasthenia gravis Review of diagnosis and management, Nerve & :lIu.~/e 1 : 190-205. Pinching, A.J., D.K. Peters and J. Newsom-Davis (1976) Remission of myasthenia gravis following plasma exchange, Lancet, ii: 1373 1376. Reuther, P,, B.W. Rulpias, H.G. Mertens and G. Hertel (1979) Anti-acetylcholine receptor antibody under tong-term azathioprine treatment in myasthenia gravis. In: P.C. Dau (Ed.), Plasmapheresis and the lmmunobiology o[' Myasthenia Gravis, Houghton-Mifflin Company, Boston, MA, pp. 329 342. Vincent, A. and J. Newsom-Davis (1980) Anti-acetylcholine receptor antibodies, J. Neurol. Neurom,':~. Psychiat., 43: 590-600.