Updating motor unit number estimation (MUNE).

Motor unit number estimation (MUNE) is a unique electrophysiologic technique that can provide a numeric estimate of the number of axons innervating a muscle or group of muscles. The first technique was first described in 1971, and since then different techniques have been developed to address specific methodologic issues. The field was reviewed in this journal in 2001, and this update covers new information and uses of MUNE over the past five years. These include models of muscles that allow evaluation of MUNE techniques and comparisons between techniques. There have been further investigations of specific technical aspects of MUNE. Modifications to MUNE techniques have been offered that permit more rapid acquisition of data. MUNE has been used in clinical situations to elucidate the pathophysiology features of axonal loss in a number of disorders. There is now more experience with MUNE as endpoint measures in clinical trials.