The importance of quantitative electron microscopy in studying hypertrophic neuropathies. A comparison between a case of Déjérine Sottas disease (HMSN III) and a case of the hypertrophic form of Charcot-Marie-Tooth disease (HMSN I).

The electron microscopic features and quantitative morphometric data of the sural nerve in Déjérine-Sottas disease (HMSN III) and in the hypertrophic form of Charcot-Marie-Tooth disease (HMSN I) are reported. Both forms are characterized by onion bulb formations, but they differ in: a) increased incidence of mucoid connective tissue in DS disease; b) higher incidence of demyelination in DS disease; c) uniformly small size of the remaining myelinated fibers in DS disease; d) larger and more developed onion bulbs in DS disease; e) clusters of 2-4 myelinated fibers in the core of onion bulbs of CMT disease; f) peripheral concentric lamellae with the typical aspects of the denervation bands of the unmyelinated fiber type in the onion bulbs of the CMT disease; g) non-involvement of unmyelinated fibers in DS disease. These differences permit two types of onion bulbs to be distinguished, and suggest a different pathogenesis. Electron microscopy, coupled with quantitative determinations, permits a deeper insight into the formation modalities of onion bulbs and may help in the diagnosis of the different forms of hypertrophic neuropathies.