Repetitive nerve stimulation testing of the ulnar nerve was systematically performed on 21 normal controls and 120 patients with myasthenia gravis (MG). Diagnostic sensitivity increased from 0% in MG in remission and 17.2% in ocular MG to 100% in severe generalized MG. Six types of responses were observed in MG and could be classified into two distinct patterns based upon disease severity: ( 1 ) in mild MG, an abnormal decremental response at low rate of stimulation, normal response at high rate of stimulation, and prominent posttetanic facilitation and exhaustion phenomena; and (2) in severe MG, abnormal decremental responses at low as well as high stimulation rates and less common posttetanic facilitation and rare posttetanic exhaustion phenomena. This difference is most likely due to the severity of the neuromuscular block in MG. Oh Methods and MaterialsFor study of neuromuscular transmission we used the Harvey-Masland method with the surface-recording electrode on the abductor digiti quinti muscle and the surfacestimulating electrode on the transsulcal segment of the ulnar nerve [ 111. For the recording electrode, the active electrode was placed over the belly of the muscle and the reference electrode over the tendon. For stimulation of the nerve, we used the supramaximal 0.2 msec stimulus duration.Each subject lay on a bed with the forearm and hand fixed on a stand with a heavy base (281. The nerve was stimulated at 3isec for 2 seconds, at 5isec for 1 sec-ond, and at 50/sec for I second, using DISA 14 and 1500 EMG machines. There was at least a I-minute interval between each test. Immediately and 4 minutes after tetanic stimulation at 50isec, the nerve was stimulated at S/sec for 1 second each time.The peak-to-peak amplitude of each muscle potential was measured. The percentage of decrement or increment was calculated by comparing the first response with the lowest or highest among the first five responses at the low rate of stimulation and during t h e first second at the high rate of stimulation. When the results differed by 2 standard deviations from the mean in controls, they were considered abnormal.Posttetanic facilitation and exhaustion phenomena were defined as having occurred when the decremental response at Sisec immediately after and 4 minutes after tetanic stimulation showed improvement or aggravation, respectively, compared with the response at 5isec prior to tetanic stimulation.The present analysis is based on 2 1 normal controls a d 120 patients with MG. M G was diagnosed by a combination of clinical examination and consistent reversal of signs and symptoms upon parenteral administration of edrophonium or neostigmine. Among 103 patients with symptomatic MG, the test was performed in 79 before any medication was started (no-anticholinesterase group), in 18 after anticholinesterases had been discontinued for at least 12 hours (anticholinesterase-off group), and in 6 patients with myasthenic crisis within 6 hours after administration of anticholinesterase medication.

In the repetitive nerve stimulation (RNS) test, 8-10% decremental response has been used as the normal limit for all muscles in many laboratories.' However, there has been some recent evidence to suggest that 8-10% decrement is not uniformly applicable to all muscles.We performed the RNS test on abductor digiti quinti (ADQ), flexor carpi ulnaris (FCU), deltoid, and orbicularis oculi (00) muscles in normal individuals using "stickup" surface recording electrodes and stimulating at a rate of 2-5/sec. For ADQ and FCU 50/sec stimulation for 1 second was added. For deltoid, surface and needle electrodes were used for stimulation. Skin temperature was controlled distally above 32 'C and proximally at 33 'C. Other technical details have been published previously.' An artifact-free test was obtained on deltoid in 60% of cases with surface stimulation and in 70% with needle stimulation; it was obtained in all cases on other muscles. Normal limits for 2-5/sec stimulation were different for each muscle: 5-7% decremental response for ADQ, 8% for 0 0 , 8 -11% for FCU, and 12-13% for deltoid