A new regional curare test of the elbow flexors in myasthenia gravis

Electrical and mechanical responses of the elbow flexors (EFs) and the adductor pollicis muscle (ADP) were evoked in 31 patients with myasthenia gravis (MG). Thirteen patients with moderate or severe involvement showed a decrement during trains of repetitive stimuli in both muscle types, greater in the proximal ones than in the distal one. Seven of 18 patients with mild generalized or ocular MG showed abnormalities in the EFs, and 4 patients showed abnormalities in the ADP. A regional curare test was performed in the EFs of 11 patients with borderline or no abnormalities in the EFs and the ADP. All patients were more sensitive to curare than were control subjects; in 2, a decrement outside the range of controls could only be provoked in the partly curarized muscle during posttetanic exhaustion. Excitation-contraction coupling, as evidenced by the staircase phenomenon and after correction for blackade of fibers, was abnormal in 5 of 31 patients in the EFs, and in 11 patients in the ADP. In both muscles, the action potential was a more sensitive criterion of abnormality than the mechanical response. The decrement in the action potentials during 3/sec stimuli gave the largest diagnostic yield.