Sensitivity of MUP parameters in detecting change in early ALS

•Detailed knowledge on the earliest changes of the motor unit morphology in ALS is critical for evaluating reinnervation with electromyography, in future clinical trials with drugs promoting axonal sprouting.•Increased motor unit duration and jitter are very sensitive and consistent markers of early motor unit adaptation in very early affected muscles in ALS.•Mean motor unit duration is a measure easily applicable in clinical trials of compounds considered likely to be of value in promoting reinnervation.

ObjectivesWe aimed to identify the most appropriate MUP parameter to evaluate reinnervation in very early ALS.MethodsWe studied tibialis anterior (TA), initially of normal strength with normal MUP analysis parameters, in 15 patients with ALS of recent onset. They were studied at the initial diagnostic assessment, and then 3 and 6 months later. Spontaneous EMG activity was recorded. Conventional MUP analysis included mean amplitude, mean area, mean duration, mean number of phases, mean number of turns, % polyphasic potentials, mean jitter, % unstable pairs and % pairs with blocking. Non-parametric statistics were utilised in the analysis.ResultsFasciculations were recorded in 72% in TA and increased jitter in 33% at study entry, but without EMG features of denervation. Mean amplitude, mean duration, mean area and the three measures of neuromuscular transmission increased significantly and linearly at each evaluation. Median duration showed the lowest variation and, together with jitter, the largest relative time effect.ConclusionsMean duration and mean jitter are the most effective measures of early reinnervation in a very early affected muscle, in ALS.SignificanceMean MUP duration is a simple and easy measure that should be useful in evaluating reinnervation, for example in a future clinical trial.