Hereditary myoclonus and progressive distal muscular atrophy

Abstract

Myoclonus occurs in a variety of pathological conditions, some inherited. We recently evaluated 3 members of a Louisiana‐Texas family with an autosomal dominant disorder manifested by adult‐onset, generalized, stimulus‐sensitive myoclonus and slowly progressive distal muscle weakness and wasting. The analyses of cerebrospinal fluid homovanillic acid and 5‐hydroxyindoleacetic acid before and after probenecid provided some evidence of impaired turnover of central dopamine and serotonin. Treatment with clonazepam resulted in complete and lasting improvement of the myoclonus. A postmortem examination in 1 member of the family revealed chiefly neuronal degeneration of the anterior horn cells, Clarke's nucleus, and the lower cranial nerve nuclei. A similar syndrome has not previously been reported.