MULTIFOCAL MOTOR NEUROPATHIES WITH CONDUC TION BLOCKS - 39 CASES

Clinical, biological and electrophysiological features from a cohort o f 39 multifocal motor neuropathies with conduction blocks (NMM with CB ) have been studied. There were 29 males and 10 females with an averag e age of 47.3. At the first evaluation, the mean duration of the sympt oms was of 8 years with extremes between 1 and 28. Pain and paresthesi as were present in respectively 10 and 18 p. 100 of the patients. Fasc iculations and cramps were observed in more than 2/3 of the cases. Thr ee patients had tremor at rest. Upper limb muscular weakness was the p redominant initial symptom (84.6 p. 100). The weakness always affected distal and unilateral muscles. Radial and cubital nerve distribution are mainly affected and in half of the cases an unilateral motor defic it in lower limb was associated. Muscle atrophy was frequent (74 p. 10 0) and rapidly developped in the first 2 years. Reflexes were decrease d or absent in 64 p. 100. In 78 p. 100 of cases, biological study show ed normal serum immunoelectrophoresis and CSF: IgM anti-GM1 antibodies were found in 24/36 patients. Very high titers were found in 5 cases. All patients had CB in upper limbs. The preferential localizations of the CB were equally at the median and ulnar nerves. Only 7 patients h ad CB localized to the lower limbs. In many cases, marked reduction of the motor amplitude prevented the detection of CB, marked reduction o f the motor amplitude prevented the detection of CB. Moderate fibrilla tion potentials were found in 28 p. 100 of patients. Giant muscular un it potentials were frequent (21/39). F-waves in nerve with CB were alw ays abnormal with marked increased latencies. Late responses sometimes seemed to be repeater F-waves. Axon reflexes were detected in 5 cases . The late responses abnormalities could precede the block. Clinical, biological and electrophysiological described arguments could may dist inguish NMM with CB from motor neuron disease and relate them to the g roup of chronic demyelinating neuropathies.