Re-evaluation of Repetitive Nerve Stimulation Test in Myasthenia Gravis and Myasthenic Syndrome

Transcription

1 Re-evaluation of Repetitive Nerve Stimulation Test in Myasthenia Gravis and Myasthenic Syndrome Bum Chun Suh, M.D., Byung Ok Choi, M.D., Hwa-Young Cheon, M.D., Seung Min Kim, M.D., Il Nam Sunwoo, M.D. Department of Neurology, Yonsei University College of Medicine, Seoul, Korea Background : The repetitive nerve stimulation (RNS) test is a useful tool in the evaluation of neuromuscular transmission disorders. In our laboratory, we frequently use Oh s method, which tests 5 kinds of muscles (flexor carpi ulnaris (FCU), abductor digiti quinti (ADQ), orbicularis oculi, nasalis and trapezius) with 3 kinds of low rate stimulation (LRS) and high rate stimulation (HRS). This method has the advantage of high sensitivity, but is time consuming and painful to patients. So, we tried to re-establish the stage of RNS to overcome this problem and to create a useful test. Methods : We analyzed RNS data from 369 patients, retrospectively. The number of patients with myasthenia gravis (MG) was 357 and the number with myasthenic syndrome was 12. We compared the sensitivity of individual muscle as well as individual stimulation rate. And we analyzed the results of MG and myasthenic syndrome to verify the usefulness of HRS. Results : The sensitivity of RNS (LRS) was 69.7% in MG (generalized symptom 86.4%, only ocular symptom 40.3%). The sensitivity was higher with 3 pps and 5 pps than with 2 pps, while the exclusion of 2 pps did not affect the sensitivity. We found only 3 cases (1.0%) with post-tetanic exhaustion (PTE) in MG patients with negative results on LRS. The distributions of resting CMAP and post-exercise CMAP were different between MG and myasthenic syndrome. In most cases of myasthenic syndrome, the resting CMAP of ADQ and FCU was below 4.0 mv and post-exercise CMAP of ADQ and FCU was above 50%. Conclusions : LRS may be done with only 3 and 5 pps, and HRS of the ulnar nerve was helpful only if there was a suspicion of myasthenic syndrome (resting CMAP<4.0 mv or post-exercise CMAP>50%, in ADQ & FCU) or a borderline decremental response in LRS. J Korean Neurol Assoc 18(3):319~325, 2000 Key Words : Repetitive nerve stimulation test, Myasthenia gravis, Myasthenic syndrome Il Nam Sunwoo, M.D. Copyright 2000 by the Korean Neurological Association 319

2 Table 1. Clinical characteristics Diagnosis Number Age* Sex(M:F) MG S-OCU ±18.3 1:1.2 S-GEN Total ± ±15.6 1:2.4 1:1.8 MSD LEMS Overlap Total ± ± ±14.2 2:1 2:1 2:1 *: Age±standard deviation MG: myasthenia gravis, MSD: myasthenic syndrome S-OCU: only ocular symptom, S-GEN: gereralized symptom LEMS: Lambert-Eaton myasthenic syndrome Overlap: overlap syndrome 320 J Korean Neurol Assoc / Volume 18 / May, 2000

3 Table 2. Sensitivity of repetitive nerve stimulation test on individual muscles in myasthenia gravis Type ADQ FCU OCU NSA TRP Total S-OCU 5/123* (4.1%) 3/123 (2.4%) 42/124 (33.9%) 17/64 (26.6%) 14/85 (16.5%) 52/129 (40.3%) S-GEN 93/224 (41.5%) 121/226 (53.5%) 165/224 (73.7%) 80/114 (70.2%) 101/163 (62.9%) 197/228 (86.4%) Total 98/347 (28.2%) 124/349 (34.4%) 207/348 (59.5%) 97/178 (54.5%) 115/248 (46.4%) 249/357 (69.7%) *: Numerator is the number of positive results and denominator is the total tested number. : 95% confidence interval, which are compared with ADQ : 95% confidence interval, which are compared with ADQ and FCU : 95% confidence interval, which are compared with ADQ, FCU and TRP ADQ: abductor digiti quinti, FCU: flexor carpi ulnaris, OCU: orbicularis oculi, NSA: nasalis, TRP: trapezius, S-OCU: only ocular symptom, S-GEN: gereralized symptom Table 3. Sensitivity of repetitive nerve stimulation test with individual stimulation rates & muscles in myasthenia gravis Type Stim.(pps) ADQ FCU OCU NSA TRP S-OCU 2 1.6% 1.6% 26.6% 15.6% 11.8% 3 2.4% 2.5% 30.9% 20.3% 14.3% 5 1.6% 2.4% 29.8% 21.9% 14.1% S-GEN % 43.8% 64.3% 61.9% 52.1% % 50.7% 67.9% 65.5% 54.9% % 50.6% 71.5% 66.4% 54.7% Stim.: stimulation rate, pps: pulse per second ADQ: abductor digiti quinti, FCU: flexor carpi ulnaris, OCU: orbicularis oculi, NSA: nasalis, TRP: trapezius, S-OCU: only ocular symptom, S-GEN: gereralized symptom J Korean Neurol Assoc / Volume 18 / May,

4 Table 4. Distribution of resting-cmap in myasthenic syndrome & myasthenia gravis Muscle Dx. <3.9* ~ ~ Total ADQ MSD 8 1 3(3) (3) MG FCU MSD 10(3) (3) MG *: mv, : Normal CMAP of FCU3, : Normal CMAP of ADQ4 ( ): Number of overlap syndrome ADQ: abductor digiti quinti, FCU: flexor carpi ulnaris, Dx: diagnosis, MG: myasthenia gravis, MSD: myasthenic syndrome Table 5. Distribution of post-exercise CMAP in myasthenic syndrome & myasthenia gravis Muscle Dx <0% 0-24% 25-49% 50-74% 75-99% 100% Total ADQ MSD 0 1(1) 1 2 1(1) 7(1) 12(3) MG FCU MSD 0 1 1(1) 1 1 6(2) 10(3) MG ( ): Overlap syndrome ADQ: abductor digiti quinti, FCU: flexor carpi ulnaris, Dx: diagnosis, MG: myasthenia gravis, MSD: myasthenic syndrome Table 6. Comparison of resting-cmap & post-exercise CMAP of ADQ in myasthenic syndrome Resting-CMAP >4.0 mv 4.0 mv Total Post-exercise CMAP <50% 1(1)* 1 2(1) 50% 3(2) 7 10(2) Total 4(3) 8 12(3) *: A case of overlap syndrome that resting-cmap is 0.2 mv and post-exercise CMAP is 510% on FCU. ( ): Number of overlap syndrome 322 J Korean Neurol Assoc / Volume 18 / May, 2000

5 Table 7. Comparison of post-tetanic CMAP & post-exercise CMAP in myasthenic syndrome Post-tetanic CMAP 100% 50~100% <50% ADQ FCU ADQ FCU ADQ FCU Post-exercise CMAP 100% 7(1) 5(2) ~100% 1 0 2(1) 2(1) 0 0 <50% (1) 1 Total 8(1) 6(2) 3(1) 3(1) 1(1) 1 ( ): Number of overlap syndrome ADQ: abductor digiti quinti, FCU: flexor carpi ulnaris ADQ + FCU R-CMAP P-CMAP R-CMAP4.0mV or P-CMAP50% LRS HRS (+) (+) ;Myasthenic syndrome R-CMAP4.0mV & P-CMAP50% 7~10% ADQ + FCU LRS(3-5 pps) 10% ;Myasthenia gravis (56.2%) HRS PTE <7% OCU + NSA LRS(3-5 pps) 10% ;Myasthenia gravis (+ 38.4%) <10% TRP LRS(3-5 pps) 10% ;Myasthenia gravis (+ 5.4%) <10% Figure 1. Strategy for repetitive nerve stimulation test in myasthenia gravis and myasthenic syndrome. ( ): expected additive effect for diagnosis of myasthenia gravis R-CMAP: resting CMAP, P-CMAP: post-exercise CMAP J Korean Neurol Assoc / Volume 18 / May,

6 01. Oh SJ. Clinical electromyography: case studies. 1st ed. Baltimore, Williams & Wilkins, 1998: Desmedt JE, Borenstein S. Diagnosis of myasthenia gravis 324 J Korean Neurol Assoc / Volume 18 / May, 2000

7 by nerve stimulation. Ann NY Acad Sci ; : Kwon KH, Lee SA, Sunwoo IN. Quantitative change of repetitive nerve stimulation test in myasthenia gravis. J Korean Neurol Assoc 1992;10: Sunwoo IN. Effects of age, sex and height on nerve conduction studies. J Korean Neurol Assoc 1992;10: Lange DJ. Electrophysiologic testing of neuromuscular transmission. Neurology 1997;48(suppl 5):S18-S Schumm F, Stohr M. Accessory nerve stimulation in the assessment of myasthenia gravis. Muscle Nerve ; 7 : Keesey JC. AAEE minimonograph #33: electrodiagnostic approach to defects of neuromuscular transmission. M u s c l e N e r v e ; 1 2 : Kimura J. Electrodiagnosis in diseases of nerve and mus - cle: principles and practice. 2nd ed. Philadelphia: F.A. Davis Company, 1989; Hwang SC, Park KH, Kim GH, Choi MS, Jung DS, Kim SW. The response to low rate stimulation of repetitive nerve stimulation test after intravenous tensilon injection on patients with myasthenia gravis. J Korean Neurol Assoc ; 1 0 : Howard JF, Sanders DB, Massey JM. The electrodiagnosis of myasthenia gravis and the Lambert-Eaton myasthenic syndrome. Neurol Clin North Am ; 1 2 : Sanders DB. Lambert-Eaton myasthenic syndrome: clinical diagnosis, immune-mediated mechanisms, and update on therapies. Ann Neurol 1995;37(suppl 1):S63-S Maddison P, Newsom-Davis J, Mills KR. Distribution of electrophysiological abnormality in Lambert-Eaton myasthenic syndrome. J Neurol Neurosurg Psychiatry 1998;65: Jablecki C. Lambert-Eaton myasthenic syndrome. M u s c l e N e r v e 1984;7: J Korean Neurol Assoc / Volume 18 / May,