[Familial case of myotonia with muscular hypertrophy, weakness corrected by effort and atrophy of type II fibers].

A 35 years old man has a non progressive muscle disease which appeared when he was 6. Clinically, there is a slight muscle hypertrophy, an important spontaneous myotonia and a curious muscle weakness, quite marked on the first efforts, but disappearing entirely after a few muscle contractions. The E.M.G. is normal but for the myotonic reaction. Muscle biopsy shows a selective atrophy of type II fibers. The disease is a genetic one, a sister and a brother of our patient having noticed the same symptom. The place of this disease among the congenital myotonias is discussed.