Monitoring the short-term effect of intravenous immunoglobulins in multifocal motor neuropathy using motor unit number index

Objective: To determine whether motor unit number index (MUNIX) is pertinent to monitor the effect of intravenous immunoglobulins (IVIg) in multifocal motor neuropathy (MMN). Methods: MUNIX was assessed longitudinally in 7 MMN patients and 17 healthy controls in the abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles. A MUNIX sum-score and a compound muscle action potential (CMAP) sum-score were calculated by summing up the scores of APB and ADM. MMN patients were evaluated on the first day of IVIg infusion, 5 MMN patients were evaluated 22 days after IVIg infusion, and 3 MMN patients were evaluated 1 month after two IVIg infusions. Results: Intraclass correlation coefficient of the MUNIX sum-score in healthy controls was 0.85, showing good test-retest reproducibility. MUNIX and CMAP sum-scores were lower in MMN patients than in healthy controls (p < 0.01 and 0.02, respectively). MUNIX sum-score improved in three of the five patients 22 days after IVIg infusion and in two of the three patients 1 month after 2 IVIg infusions, whereas CMAP sum-score improved in only one patient in both evaluations. Conclusions: In this preliminary study, MUNIX seems to be a reliable and sensitive tool to monitor the short-term efficiency of IVIg in MMN. Significance: MUNIX can help monitor IVIg treatment in MMN. (C) 2016 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.