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 brain stem. It is, however, difficult to clinically evaluate the degree of motor neuron degeneration, which stresses the need for biomarkers to detect the remaining neuronal function.
Methods: We performed motor unit number estimation (MUNE) in 52 SBMA patients to investigate whether this method could be a potential biomarker of SBMA. We also re-evaluated MUNE one year later in a subgroup of the patients.
Results: The number of functioning motor units was remarkably reduced in SBMA patients compared to controls, and was correlated with both ipsilateral grip power and disease duration. A longitudinal analysis demonstrated a further reduction of motor units within one year.
Conclusions: Our results suggest that MUNE is an electrophysiological parameter that reflects the severity and progression of motor neuron degeneration in patients with SBMA.