NEUROPHYSIOLOGICAL EVALUATION IN MYASTHENIA-GRAVIS - A COMPREHENSIVE STUDY OF A COMPLETE PATIENT POPULATION

Electrical and mechanical responses to single shocks, slow and fast ne rve stimulation (RNS), quantitated EMG, anti-acetylcholine receptor (A ChR) and anti-striated muscle (SM) antibodies (ab) were determined in 145 patients with myasthenia gravis (MG). Anti-AChR ab were found in 9 3% of the myasthenic sera. Decrement of muscle and mechanical response s occurred in 72% and 49%, respectively, the diagnostic yield being po sitively related to severity of MG. Anti-AChR ab were found in 81% of patients without RNS abnormalities. Decrement at RNS occurred in 33% o f the cases without anti-AChR ab compared with 78% of those with eleva ted titres. Regional curare test (RCT) was diagnostic in 75% of cases with normal RNS. As the combined diagnostic yield of RNS and anti-AChR ab was 96%, RCT and single fibre EMG are rarely indicated. Post-tetan ic facilitation and exhaustion, and an abnormal staircase phenomenon o ccurred in 25%, 44% and 37%, respectively. None of these parameters co rrelated with severity, type or onset of MG. EMG evidence of myopathy, positively correlated with the presence of anti-SM ab, occurred in 19 % of patients examined, 3 times more frequent in those with late onset of MG than in those with early onset; thus myopathy of possible autoi mmune origin may coexist with MG. An adequate electrophysiological dia gnostic strategy for MG patients is proposed.