Association Between MScanFit Motor Unit Number Estimation and Clinical Function and Response to Immunoglobulin Therapy in Chronic Inflammatory Demyelinating Polyneuropathy.

Objective: Loss of motor units in chronic inflammatory demyelinating polyneuropathy is difficult to assess by conventional nerve conduction due to collateral innervation. We aimed to assess the association between a motor unit number estimate (MUNE) derived from the compound muscle action potential (CMAP) scan using MScanFit and hand function and the clinical response to intravenous immunoglobulin (IVIG).

Methods: Forty-nine CIDP patients and 52 control subjects were included. CMAP scan recordings were obtained from the right abductor pollicis brevis muscle. The primary outcome was the correlation between MUNE and the duration of the nine-hole-peg test (9-HPT) at baseline and the change in the duration of the 9-HPT following treatment with IVIG. Secondary outcomes were grip strength, 10-m-walk test, six-spot-step test, medical research council sum score, inflammatory neuropathy cause and treatment sensory sum score, overall neuropathy limitations scale, and the Rasch-built overall disability scale (R-ODS).

Results: MScanFit analysis suggested both loss of motor units (reduced MUNE (p = 0.022) and N50 (p < 0.0001)) and collateral reinnervation (increased median amplitude (p < 0.0001) and size of the largest unit (p < 0.0001)) in CIDP patients compared to controls. In CIDP patients, there was a statistically significant correlation between MUNE and the duration of the 9-HPT (Spearman's r = -0.342; p = 0.016). Further, patients with a low MUNE had the largest reduction in the duration of the 9-HPT following IVIG treatment (r = -0.577; p = 0.043). MUNE also correlated significantly with R-ODS (r = -0.722; p = 0.007).

Conclusions: MScanFit MUNE could be a useful method for assessing motor axonal loss in CIDP, which correlates with the clinical function and treatment response.