UPPER MOTOR-NEURON DYSFUNCTION REDUCES THE EMG EVIDENCE OF MYASTHENIA-GRAVIS

Hyposensitivity to the action of nondepolarizing muscle relaxants has been frequently observed in patients with upper motor neuron dysfuncti on and in patients treated with antiepileptic drugs. To ascertain whet her the same conditions are also characterized by a reduced sensitivit y to the effects of anti-acetylcholine-receptor antibodies occurring i n myasthenia gravis, bilateral investigations of neuromuscular transmi ssion were conducted on proximal and distal muscles of a myasthenic pa tient with a long history of hemiparesis and epilepsy. It was observed that electromyographic evidence of myasthenia gravis was absent in di stal muscles (and low in proximal ones) of the paretic side. Even thou gh the influence of antiepileptic treatment could not be assessed with certainty in this patient, indirect evidence suggests that hyposensit ivity to anti-acetylcholine-receptor antibodies is an unlikely consequ ence of neuromuscular changes induced by anticonvulsants.