MULTIFOCAL MOTOR NEUROPATHY WITH CONDUCTION BLOCK - A STUDY OF 24 PATIENTS

Twenty four patients with pure motor neuropathy are reported. The chro nic motor involvement associated with fasciculations and cramps, mainl y in the arms, led, in most patients, to an initial diagnosis of motor neuron disease. In some patients (nine of 24), there was no appreciab le muscle atrophy. Tendon reflexes were often absent or weak. The find ing of persistent multifocal conduction block confined to motor nerve fibres raises questions about the nature and the importance of this sy ndrome. Segmental reduction of motor conduction velocity occurred at t he site of the block, but significant slowing of motor nerve conductio n was not found outside this site. The response to intravenous IVIg tr eatment seems to be correlated with the absence of amyotrophy. Patient s with little or no amyotrophy had an initial and sustained response t o IVIg, and did not develop amyotrophy during the follow up study. The y could be considered to have a variant of chronic inflammatory demyel inating polyneuropathy. Patients with pronounced amyotrophy independen t of the disease duration did not respond as well to IVIg treatment, s uggesting the existence of a distinct entity. Among the patients treat ed about two thirds who had an initial good response to IVIg had high or significant antiganglioside GM1 (anti-GM1) antibody titres, but the re was no correlation between the high titres before treatment and lon g lasting response to IVIg treatment.