Myotonia congenita--a cause of muscle weakness and stiffness.

BACKGROUND

A 56-year-old woman was referred to a neurogenetic clinic with a history of stiffness and transient weakness. A previous needle electromyogram had confirmed the presence of myotonia, but a muscle biopsy had revealed no evidence of dystrophy.

METHODS

Neurological examination, electrophysiological studies and genetic testing.

METHODS

Recessive myotonia congenita (Becker's disease).

RESULTS

Explanation of the nature of the disease and treatment with mexiletine 200 mg twice daily.