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

To 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.

17 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.

MUNIX 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.

MUNIX is related to motor impairment and disability in anti-MAG neuropathy and MUNIX is modified after immunosuppressive treatment.

Considering its advantages, MUNIX may be a suitable test to evaluate anti-MAG neuropathy in clinical trials.