Subclinical motor involvement in non-systemic vasculitic neuropathy determined by the motor unit number estimation method MScanFit.

INTRODUCTION/ AIMS: Non-systemic vasculitic neuropathy (NSVN) is characterized by a predominant lower-limb involvement in many patients. Motor unit changes in upper extremity muscles have not been investigated in this subgroup, but might be of interest to improve the understanding of the multifocal nature of the disease and counseling of patients on potential future symptoms. We aimed to investigate subclinical motor involvement in upper extremity muscles of patients with lower-limb predominant NSVN using the new motor unit number estimation (MUNE) method MScanFit.

METHODS: In this single center cross-sectional study, 14 patients with biopsy-proven NSVN, with no clinical signs of upper extremity motor involvement, were investigated and compared to 14 age-matched healthy controls. All participants were assessed clinically and by the MUNE method MScanFit to the abductor pollicis brevis muscle.

RESULTS: The number of motor units and peak CMAP-amplitudes were significantly reduced in patients with NSVN (p = 0.003; p = 0.004). Absolute median motor unit amplitudes and CMAP-discontinuities were not significantly different (p = 0.246; p = 0.1). CMAP-discontinuities were not significantly correlated with motor unit loss (p = 0.15, Rho = 0.4). The number of motor units did not correlate with clinical scores (p = 0.77, Rho 0.082).

DISCUSSION: Both MUNE and CMAP-amplitudes showed motor involvement in upper extremity muscles in lower-limb predominant NSVN. Overall, there was no evidence of significant reinnervation. Investigations of the abductor pollicis brevis muscle did not correlate with the overall functional disability of the patients.