Motor unit number index (MUNIX) in patients with anti-MAG neuropathy

•In anti-MAG neuropathy, motor impairment and disability are related to MUNIX results.•Rituximab therapy increases motor unit number estimated by MUNIX in anti-MAG neuropathy.•In clinical trials, motor unit number estimated by MUNIX may serve as a possible outcome measure.

ObjectiveTo investigate the relationship between Motor Unit Number Index (MUNIX) and functional scales in patients with anti-Myelin Associated Glycoprotein (MAG) neuropathy and to know if MUNIX is modify after rituximab (RTX) therapy.Methods17 patients were enrolled, of whom 6 were prospectively evaluated during one year after RTX treatment. MUNIX technique was assessed in abductor digiti mini (ADM), abductor pollicis brevi (APB) and tibialis anterior (TA) muscles. MUNIX sum score was calculated by adding the results of ADM, APB and TA muscles.ResultsMUNIX sum score was correlated with overall neuropathy limitation scale (ONLS) (r = −0.55, p = 0.02), grip strength in dominant hand (r = 0.63, p = 0.01) MRC testing (r = 0.71, p < 0.001) and CMAP sum score (r = 0.71, p = 0.001). Twelve months after RTX, four patients improved their disability measured on the ONLS score, five patients had improved MUNIX sum score with a median increase of 37% compared to initial evaluation.ConclusionsMUNIX is related to motor impairment and disability in anti-MAG neuropathy and MUNIX is modified after immunosuppressive treatment.SignificanceConsidering its advantages, MUNIX may be a suitable test to evaluate anti-MAG neuropathy in clinical trials.