[Fasciculation potential and ALS diagnosis].

Fasciculations and fasciculation potentials (FPs) have been long known as a characteristic feature of amyotrophic lateral sclerosis (ALS). In this article, the history of the researches on fasciculation and FPs is first reviewed. The word and concept of fasciculation was first properly defined by Denny-Brown and Pennybacker (1938). It is noteworthy that they already stressed the necessity of strict discrimination of FPs from the "contraction fasciculation", a remnant of large voluntary motor unit potentials (MUPs), in this early milestone paper. FPs are rarely observed in neurogenic diseases other than ALS or disorders presenting with conduction block, i. e. they retain a high specificity in ALS diagnosis. Despite such usefulness, FPs were devaluated in the revised El-Escorial criteria. It is welcome that their value has been restored in the newer Awaji criteria. In the actual practice, correct identification of FPs would be a critical point. Remnant of voluntary MUPs is the greatest FP mimic to be differentiated. The key point for differentiation is the firing rhythm. FPs are characterized by a low-frequency and quite irregular firing, showing clustering of discharges. In contrast, voluntary MUPs are characterized by a semiregular firing.