Myopathic changes in bilateral hypertrophy of the first dorsal interosseus muscle of the hand.

A 43-year-old healthy man presented with bilateral hypertrophy of the first dorsal interosseus muscles of both hands. Neurophysiologic and laboratory examinations revealed no pathologic findings. Doubled muscle width was found by ultrasound. Myopathic changes were present in muscle biopsy with varying fiber sizes but without inflammatory features. The clinical impression of massive bilateral symmetric enlargement of the first dorsal interosseus muscles was characterized by subtle, non-specific muscular pathology.