HEREDITARY MYASTHENIC SYNDROMES WITH LATE -ONSET - USEFULNESS OF ELECTROPHYSIOLOGIC TESTS

A myasthenic syndrome was diagnosed in 3 female patients aged 37, 47 a nd 56 years. The symptoms were first noticed in childhood, and at 16 a nd 25 years. Respectively weakness and atrophy of finger extensor musc les were present in all patients. In 2 of them scapular and cervical m uscles were involved. Weakness was markedly increased by cold in every patient. Similar symptoms were noted in first degree relatives in all cases. Single nerve stimulus elicited a repetitive compound muscle ac tion potential in hand muscles. Repetitive nerve stimulation induced a myasthenic decrement in finger extensor muscles. SFEMG studies demons trated increased jitter with frequent blockings. Genetic, clinical and electrodiagnostic data were consistent with the hypothesis of the so- called <<Slow-Channel>> myasthenic syndrome. As 2 of these patients we re considered to have <<unknown myopathy>> the use of careful nerve st imulation tests is advocated in such cases.