The profile of motor unit number estimation (MUNE) in spinal and bulbar muscular atrophy

Objective Spinal and bulbar muscular atrophy (SBMA) is a lower motor neuron disease caused by the expansion of a trinucleotide CAG repeat in the androgen receptor (AR) gene. The fundamental histopathological finding of this disease is an extensive loss of lower motor neurons in the spinal cord and brainstem. It is, however, difficult to evaluate clinically the degree of motor neuron degeneration, which stresses the need for biomarkers to detect the remaining neuronal function. Methods The authors performed motor unit number estimation (MUNE) in 52 patients with SBMA, to investigate whether this method could be a potential biomarker of SBMA, and re-evaluated MUNE 1 year later in a subgroup of the patients. Results The number of functioning motor units was remarkably reduced in patients with SBMA compared with controls, and was correlated with both ipsilateral grip power and disease duration. A longitudinal analysis demonstrated a further reduction in motor units within 1 year. Conclusions The results suggest that MUNE is an electrophysiological parameter that reflects the severity and progression of motor neuron degeneration in patients with SBMA.