Rapid Voice Tremor, or “Flutter,” in Amyotrophic Lateral Sclerosis

In an attempt to clarify the origin and frequency characteristics of a rapid voice tremor, or “flutter,” in patients with amyotrophic lateral sclerosis (ALS), eight patients (four men and four women; ages 42 to 70 years) who had ALS and rapid voice tremor and an age-and sex-matched control group of eight subjects were asked to sustain the vowel /a/ and their voices were recorded for later analysis. Each segment of phonation was demodulated into amplitude and frequency components. From each subject's 8-second amplitude and frequency signals, a fast Fourier transform analysis was done on a 1-second segment previously identified perceptually as having the most apparent tremor or flutter. The results showed that patients with ALS had multiple combinations of levels and frequencies for amplitude and frequency modulations in comparison with control subjects, who had consistently low levels of modulations. In an attempt to quantify the tremor or flutter in ALS, amplitude and frequency modulations were not clearly or predominantly represented at one point along the spectrum. Nevertheless, these frequency and amplitude modulations are more prominent in patients with ALS than in normal subjects. The origins of these aberrant frequency and amplitude modulations in ALS patients remain obscure, although speculation is that they are of peripheral rather than central nervous system origin.