SummaryBackground-Spinal and bulbar muscular atrophy (SBMA) is caused by polyglutamine expansion in the androgen receptor, which results in ligand-dependent toxicity. Animal models have a neuromuscular deficit that is mitigated by androgen-reducing treatment.

MUNE, a technique used in ALS clinical trials to quantitatively assess motor neuron loss, should also be valuable in assessing progression in spinal bulbar muscular atrophy (SBMA), an x-linked neuronopathy. In ALS, instability of single motor units (SMUP) prompted Shefner9 to modify the statistical MUNE method to exclude SMUPs ≤ 40μV. It is unknown if there is a similar SMUP instability in the more chronic degenerative disease of SBMA.In this study, the standard parameter of excluding SMUP < 10 μV was compared with the exclusion of SMUP < 40 μV in the calculation of the statistical MUNE. The mean statistical MUNE, using the standard method and the Shefner method, was 60±21 to 47±23, respectively. Similar to ALS, SBMA showed an increased proportion (17%) of individual SMUPs ≤ 40 μV compared to normal controls.In conclusion, excluding SMUPs ≤ 40 μV from the statistical MUNE calculations is appropriate for SBMA subjects because their SMUPs characteristics are similar to ALS. Exclusion of the low amplitude SMUPs reduces the calculated MUNE.

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