Hypertrophic neuropathy: atypical appearances resulting from the combination of type I hereditary motor and sensory neuropathy and diabetes mellitus.

A nerve biopsy from a patient with type Ia hereditary motor and sensory neuropathy and diabetes mellitus showed hypertrophic changes of atypical appearance. The onion bulbs were composed of a central core of Schwann cells, with or without associated axons, embedded in concentrically arrayed layers of collagen fibrils. These were surrounded either by highly attenuated Schwann cell processes or by fibroblasts. The biopsy showed a severe loss of myelinated axons. It is suggested that it is necessary for the supernumerary Schwann cells of the onion bulbs to be stabilized by associated unmyelinated axons. If these are lost, the Schwann cells atrophy and disappear.