Role of activity-dependent conduction block in the diagnosis of primary demyelinating polyneuropathy.

Motor conduction block is one of the well-known neurophysiologic features of primary demyelinating polyneuropathy. In contrast, activity-dependent conduction block (motor conduction block after brief maximum voluntary contraction) is a "rare" neurophysiologic finding in primary demyelinating polyneuropathy. We are reporting the first known case of multifocal acquired demyelinating sensory and motor polyneuropathy with a well-documented activity-dependent conduction block of the ulnar nerve at the forearm segment that transformed into a typical motor response with abnormal temporal dispersion.