Myotonic dystrophy with nerve hypertrophy. Report of a case with electrophysiological and ultrastructural study of the sural nerve.

A striking enlargement of peripheral nerves was observed in a patient with myotonic dystrophy (Steinert's disease). Clinical findings disclosed a polyneuropathy which was confirmed by electrophysiological and morphological investigations. Myopathic as well as neurogenic alterations were found on electromyography in wasted hand muscles. The prominent finding on ultrastructural study of sural nerve biopsy was an important collagen infiltration with rather few "onior bulb" formations. This extensive endoneural collagen formation appeared to be responsible for the nerve hypertrophy. Evidence of segmental demyelination and remyelination was also found. Glycogen deposits were present in some myelinated axons and is some Schwann cells. Peculiar crystalline inclusions were observed in fibroblasts processes. The relation between myotonic dystrophy and polyneuropathy remains a matter of discussion.