Neurophysiological evaluation in myasthenia gravis. A comprehensive study of a complete patient population.
Electrical and mechanical responses to single shocks, slow and fast nerve stimulation (RNS), quantitated EMG, anti-acetylcholine receptor (AChR) and anti-striated muscle (SM) antibodies (ab) were determined in 145 patients with myasthenia gravis (MG). Anti-AChR ab were found in 93% of the myasthenic sera. Decrement of muscle and mechanical responses occurred in 72% and 49%, respectively, the diagnostic yield being positively related to severity of MG. Anti-AChR ab were found in 81% of patients without RNS abnormalities. Decrement at RNS occurred in 33% of the cases without anti-AChR ab compared with 78% of those with elevated 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-tetanic facilitation and exhaustion, and an abnormal staircase phenomenon occurred in 25%, 44% and 37%, respectively. None of these parameters correlated 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 autoimmune origin may coexist with MG. An adequate electrophysiological diagnostic strategy for MG patients is proposed.
Somnier
F E
FE
Department of Neurology, National Hosptial (Rigshospitalet), University of Copenhagen, Denmark.
Trojaborg
W
W
D000328:Adult; D001323:Autoantibodies / Q000097:blood; D003472:Curare; D004491:Edrophonium; D004558:Electric Stimulation; D004576:Electromyography; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000378:metabolism / Q000503:physiopathology*; D009469:Neuromuscular Junction / Q000502:physiology; D010812:Physical Stimulation; D011237:Predictive Value of Tests; D011950:Receptors, Cholinergic / Q000276:immunology; D009435:Synaptic Transmission / Q000502:physiology
D001323:Autoantibodies; D011950:Receptors, Cholinergic; D004491:Edrophonium; D003472:Curare