Motor unit number index (MUNIX) in chronic inflammatory demyelinating polyneuropathy: A potential role in monitoring response to intravenous immunoglobulins

OBJECTIVE: To compare motor unit number index (MUNIX) values in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and healthy controls, to assess correlations between MUNIX and clinical assessments used in CIDP and to assess short-term changes in MUNIX in CIDP following intravenous immunoglobulins (IVIg). METHODS: MUNIX sum scores were calculated from three muscles in patients and healthy controls. CIDP patients also underwent a series of clinical assessments and completed the Overall Neuropathy Limitations Scale (ONLS) and the Rasch-built Overall-Disability Scale (R-ODS). Repeat assessments were performed in CIDP patients receiving IVIg and CIDP patients not on active treatment. RESULTS: MUNIX sum scores were significantly lower in CIDP patients than healthy controls (mean values 214.0 vs 516.9, respectively; p < 0.001). MUNIX sum scores correlated with clinical assessment of motor and sensory function and ONLS and R-ODS scores in CIDP patients. Significant short-term improvements were seen in MUNIX values on repeat testing following IVIg (188.3-226.4, p = 0.001), but not in CIDP patients not receiving IVIg. CONCLUSIONS: MUNIX values show stronger correlation with commonly-used clinical assessments and disability scores than other routinely used electrophysiological parameters. Rapid improvements in MUNIX sum scores are seen following IVIg. SIGNIFICANCE: MUNIX sum score may provide an objective marker of response to IVIg.