Electrophysiological and clinical correlation in myasthenia gravis

Abstract

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.

Myasthenia gravis in children: analysis of 18 patients

“…EMG repetitive stimulation was useful in the diagnosis of our patients but, like others we found that its sensitivity correlated with the form and severity of the disease it is low in the ocular forms, increases in the generalized forms and is even higher the more severe the disease is manifested [17][18][19] .…”

Diagnostic difficulties in myasthenia gravis

“…15,20 In general, about 60-85% of patients with myasthenia gravis show a decremental response. 5,15,16 Diagnostic sensitivity increases with increasing severity of myasthenia gravis, 15,16 with positive results in 14-38% of patients with ocular involvement only (Osserman class 1) and in 83-100% of patients with an incapacitating weakness of any muscle system (Osserman class IV).…”

“…15,20 In general, about 60-85% of patients with myasthenia gravis show a decremental response. 5,15,16 Diagnostic sensitivity increases with increasing severity of myasthenia gravis, 15,16 with positive results in 14-38% of patients with ocular involvement only (Osserman class 1) and in 83-100% of patients with an incapacitating weakness of any muscle system (Osserman class IV). 3,15,16 Only 1 of our 4 patients had decremental responses on initial assessment during the period of respiratory failure, despite all being Osserman class IV and all having careful repetitive stimulation studies of the median and facial nerves.…”

Electromyographic assessment of fatiguability and recovery of orbicularis oculi in myasthenia gravis.

“…351 amplitude in response to repetitive nerve stimulation, single fiber electromyography, stapedius reflex fatiguability, tests for eye movement fatigue and detection of antibodies against the acetylcholine receptors in the serum. Many of these tests have limitations in diagnosing ocular myasthenia gravis (Oh et al 1982;Kelly et al 1982).…”