Electrodiagnostics: MUNE and MUNIX as methods of estimating the number of motor units – biomarkers in lower motor neurone disease

Routine quantitative electromyography is used for the assessment of the presence of lower motor neurone involvement and its consequences, including primary denervation and compensatory reinnervation of muscle fibres. However, it is not useful for the assessment of the motor unit number reserve. The need for a valid biomarker to evaluate lower motor neurone disease progression in such diseases as amyotrophic lateral sclerosis, and for use in clinical trials, has led to a number of studies of the methods that allow assessment of the number of motor units. In this review, motor unit number estimation (MUNE) methods with incremental stimulation and the recently developed motor unit number index (MUNIX) method, along with their technical and clinical aspects, are presented as methods which reflect motor unit loss in neurogenic processes. These electrodiagnostic tests may allow a valuable assessment of disease progression and the efficacy of new therapeutic methods in clinical trials in diseases with lower motor neurone degeneration.