Motor unit number estimation (MUNE): how may it contribute to the diagnosis of ALS?

Motor unit number estimation (MUNE) is a type of electrophysiological technique that measures the approximate number of lower motor neurons (LMNs) innervating a single muscle or a small group of muscles. Low MUNE counts provide evidence of LMN degeneration, but a single MUNE study does not determine if this loss is ongoing, recent or remote in time. Sequential change of MUNE count provides evidence for ongoing degeneration. Furthermore, sequential change in MUNE from a normal to abnormally low count provides evidence for progressive spread of signs within a region or to another region. MUNE has no established ability to identify other diseases that may provide a non-ALS explanation for the signs of LMN degeneration. If MUNE studies were to be incorporated into a future revision of the diagnostic criteria for ALS, prospective studies will be important to define more clearly the sensitivity and specificity of MUNE in patients with ALS and in patients with weakness that does not involve LMN degeneration. In addition to its potential contributions toward the diagnosis of ALS, MUNE may have greater potential in quantifying the rate of progression in studies of the natural history of ALS and the response to experimental treatment.