Hypertrophic Charcot-Marie-Tooth disease. Light and electron microscope studies of the sural nerve.

Sural nerve biopsies from 15 patients with hypertrophic Charcot-Marie-Tooth disease have been studied by light and electron microscopy. There is a considerable variation in size of onion bulbs in patients from different kinships but the appearances were similar in patients from the same kinship. Comparison of sural nerve biopsies from patients within the same kinship suggests that with increasing age there is a progressive reduction in myelinated fibre density, an increased number of fibres undergoing demyelination and an increased frequency of onion bulb formations. Motor conduction velocities were reduced in all patients and were inversely proportional to the number of onion bulb lamellae, and to the proportion of demyelinated fibres found on sural nerve biopsy. Abnormalities of unmyelinated fibres were present in all the nerves studied. There was a relative increase in the density of denervated Schwann cell subunits and collagen pockets. The findings suggest that unmyelinated fibres undergo degeneration in the disease and lend some support to the hypothesis that the primary abnormality may be neuronal.