Differential weakness of finger extensor muscles: A clinical pattern of multifocal motor neuropathy

Several studies have suggested that differential weakness in muscles supplied by the same motor nerve supports the diagnosis of multifocal motor neuropathy (MMN).

We describe the clinical, electrophysiological, neuroimaging, and laboratory findings of patients with a lower motor syndrome whose clinical presentation included differential finger extension weakness that we have seen in our neuromuscular clinic.

We identified 3 patients with hand weakness and 1 patient with asymmetric weakness of the upper extremity. Conduction blocks (CBs) were identified in 1 patient. Anti-GM1 immunoglobulin M antibodies were detected in 2 of the 3 patients tested. Only 1 patient responded to intravenous immunoglobulin (IVIg). Rituximab was administered in another patient, but we did not detect a response.

We suggest that differential finger extension weakness is a feature that may be seen in MMN, even in the absence of CB or response to IVIg. Muscle Nerve 55: 433-437, 2017.