Sensitivity of MUP parameters in detecting change in early ALS.

Objectives: We aimed to identify the most appropriate MUP parameter to evaluate reinnervation in very early ALS.

Methods: We 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.

Results: Fasciculations 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.

Conclusions: Mean duration and mean jitter are the most effective measures of early reinnervation in a very early affected muscle, in ALS.

Significance: Mean MUP duration is a simple and easy measure that should be useful in evaluating reinnervation, for example in a future clinical trial.