Hereditary motor and sensory neuropathy. Clinical, genetic and electrodiagnostic studies.

Motor conduction velocity (MCV) alone cannot separate all the cases with types I and II of hereditary motor and sensory neuropathy (HMSN). However, sensory conduction velocity (SCV) in sural nerve distinctly separated types I and II of HMSN (8). As in most of our patients with HMSN sural nerve was unexcitable, we introduced SCV estimation in the distal segments of median and ulnar nerves. So, we studied 124 patients from families with typical and uncomplicated cases of Charcot-Marie-Tooth disease (CMTD): 68 patients had the "hypertrophic" form (type I) and 56 cases the "neuronal" form (type II). In this series, 16 patients had median MCV from 35 to 45 m/s, but SCV in the median and ulnar nerves separated 7 cases with type I and 9 patients with type II of HMSN. In conclusion, the type I and II of HMSN were delimited in most of the studied cases by MCV values in the median nerve. Nevertheless, in cases difficult to be classified either into type I or II of HMSN, i.e. patients with MCV from 35 to 45 m/s, only SCV measurements in distal median and ulnar nerves segments can distinctly separate type I (a slowing over 40% from control values), indicating that this type is underlain by a process of segmental demyelination (SD), which also was confirmed by sural nerve biopsy data. In our cases with HMSN type II MCV was either normal or slightly slowed. By contrast SCV was significantly slowed (a slowing of up to 30%). In addition, we have also a few cases of complicated HMSN forms (rare variants), associated with: 1. Isaacs' syndrome; 2. "denervation-reinnervation" muscle hypertrophy; and 3. Marinesco-Sjögren syndrome. 1. In 3 patients, the clinical features of "neuronal" form of CMTD were associated with fasciculation, cramps, impaired muscular relaxation, and percussion myotonia with respective electromyographic (EMG) accompaniments, which were responsive to valproic acid therapy. 2. On the other hand 3 patients developed in addition to the Isaacs' syndrome a significant "denervation-reinnervation" muscle hypertrophy, confirmed by both morphometric data on muscle biopsy and computed tomography. In these patients there was an increased proportion of type I and a decreased one either of type IIB or of type IIA fibres, without myotonic or dystrophic features.(ABSTRACT TRUNCATED AT 400 WORDS)