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

Motor unit number estimation (MUNE) is a type of electrophysiological techn ique that measures the approximate number of lower motor neurons (LMNs) inn ervating a single muscle or a small group of muscles. Low MUNE counts provi de 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 MU NE count provides evidence for ongoing degeneration, Furthermore, sequentia l change in MUNE from a normal to abnormally low count provides evidence fo r progressive spread of signs within a region or to another region. MUNE ha s 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 sensitivit y and specificity of MUNE in patients with ALS and in patients with weaknes s that does not involve LMN degeneration. In addition to its potential cont ributions toward the diagnosis of ALS, MUNE may have greater potential in q uantifying the rate of progression in studies of the natural history of ALS and the response to experimental treatment.