Multifocal motor neuropathy with and without conduction block: a single entity?

To assess if multifocal motor neuropathy (MMN) with and MMN without conduction block (CB) are similar or distinct diseases.

The authors reviewed the clinical features and responses to IV immunoglobulin (IVIg) treatment of patients with MMN with and without CB at diagnosis, after 4 years of follow-up and at the last examination. They included all patients showing clinical features of MMN who had been followed for at least 4 years: All had asymmetric purely motor weakness with a peripheral nerve distribution, without any sensory, bulbar, or respiratory signs and without any upper motor neuron involvement.

Twenty patients had CB and 13 had no CB. Median follow-up time was 7 years. There were no differences between the two groups in term of age, sex, time from onset to diagnosis, anti-GM1 antibody titers, or CSF data. Nerve distribution, number of affected limb regions, predominant weakness in distal upper extremities, asymmetric weakness, cramps, fasciculations, and Medical Research Council sum-scores in upper and lower limbs were comparable at diagnosis, 4 years of follow-up, and last examination. Few significant differences were observed. Involvement of median nerve was less frequent at 4 years of follow-up (14/20 vs 4/13; p = 0.027) and at the last examination (17/20 vs 5/13; p = 0.009) in patients without CB. Proximal weakness was less frequent in patients with MMN without CB at the last examination (7/20 vs 0/13; p = 0.027). Fewer nerves were involved in patients without CB at the last examination (4.5 vs 2; p = 0.04). Efficacy of IVIg was similar in MNN patients without CB (8/13) and with CB (14/20; p > 0.05).

After a median follow-up time of 7 years, patients with and without conduction block showed similar clinical features and a similar response to IV immunoglobulin treatment.