Motor conduction block and conduction velocity in Lewis-Sumner syndrome and multifocal motor neuropathy

Motor conduction blocks (CBs) and decreased motor nerve conduction velocity (MCV) are both demyelination electrophysiological characteristics. Though CBs are both common in Lewis-Sumner syndrome (LSS) and multifocal motor neuropathy (MMN), they are two distinct disease groups, so their MCV and CBs electrophysiological characteristics may be different. In this paper, we aimed to discuss the relationship between CBs and MCV in Lewis-Sumner syndrome (LSS) and multifocal motor neuropathy (MMN). Sixteen patients with LSS and 11 with MMN were retrospectively collected. Motor nerve conduction studies were performed on bilateral median and ulnar nerves. 16/23 segments with CBs in MMN, and 50/53 segments with CBs in LSS had decreased conduction velocities respectively. There was significant difference in MCV between these two groups (MMN 53.1 ± 12.5 m/s; LSS 34.3 ± 17.1 m/s, mean ± SD, P < 0.05) as well as significant difference in MCV for segment with or without CBs between MMN and LSS patients (P < 0.05). Patients with LSS were prone to be found MCV decrease in segments of motor CB than patients with MMN (P = 0.017). Forty one segments in LSS patients and 6 segments in MMN had MCV ≤ 38 m/s (P < 0.05). There exist two relationships between CB and MCV no matter in LSS or MMN. The characteristics of MCV and CB can be used to distinguish these two disease groups.