Multifocal motor neuropathy: Diagnostic criteria that predict the responseto immunoglobulin treatment

As multifocal motor neuropathy (MMN) is a potentially treatable disorder, i ts differentiation from lower motor neuron disease is important. Evidence o f conduction block (CB) is considered one of the relevant criteria for the diagnosis of MMN. Strict criteria for CB may lead to underdiagnosis of MMN, however. Using a standardized examination, we studied the clinical, labora tory, and electrophysiological characteristics of 37 patients presenting wi th a lower motor neuron disorder and electrophysiological features compatib le with segmental demyelination. We propose a set of clinical, laboratory, and electrophysiological criteria for the diagnosis of MMN, which has been verified by follow-up and response to treatment with intravenous immunoglob ulins. Based on the clinical, laboratory, and electrodiagnostic features, 2 1 patients were diagnosed with definite MMN (17 responders), 7 were diagnos ed with probable MMN (5 responders), and 9 were diagnosed with possible MMN (1 responder). Age at onset, the number of affected limb regions, and the number of patients with a creatine kinase level greater than 180 U/L were s ignificantly lower in responders than in nonresponders. Elevated anti-GM1 a ntibodies and definite CB were found significantly more often in responders . The proposed diagnostic criteria may be useful in clinical practice and t herapeutic trials.