Detecting fasciculations in amyotrophic lateral sclerosis: duration of observation required.

A practical issue in the diagnosis of amyotrophic lateral sclerosis (ALS) is how long the EMG must be observed before a muscle can be declared free of fasciculations with some degree of certainty. To answer this question, the intervals between fasciculation potentials (FPs) were recorded from 53 muscles of 19 ALS patients. The distribution of the FP intervals found across the sample showed that to record a single fasciculation with a probability approaching unity, observation for up to 90 s may be required.