Clinical and ultrastructural study of a sporadic case of hereditary sensory neuropathy. Morphological evidence for a slow rate fiber degeneration.

A sporadic case of hereditary sensory neuropathy, with a clinical course and severe trophic and sensory alterations typical for type II, is presented. There was a severe loss of myelin in the sural nerve biopsy taken from the ankle. The most impressive microscopic feature was the number of rudimentary onion bulbs with an empty core which contained nude axons in the peripheral schwann cell layers; they were interpreted as vestigial structures left by the former myelinated fibers. Electron microscopy also revealed a definite involvement of unmyelinated fibers with attempted regeneration, which was confirmed by the overrepresentation of small axons on their frequency distribution curve. The whole ultrastructural picture suggested the protracted nature of the fiber involvement. This may be considered as agreeing with the slow course proposed for a system degeneration.