The nature of primary vocal tremor.

Three elderly women with marked progressive voice tremor, without other neurological symptoms, and negative family histories were investigated. All had a 4-5 Hz respiratory tremor in expiration and, to a lesser degree, in inspiration; and all had vocal tremulousness synchronous with their respiratory irregularity. Articulation of phonemes was normal. In two cases the neurological examination was otherwise normal; in the third case there was a minimal 71/2 Hz tremor in the left thumb and index finger. Simultaneous speech and vocal air pressure recordings, as well as cinematographic studies of the vocal apparatus and diaphragm were carried out. It is suggested that these cases represent primarily an action tremor of respiration, that they belong in the spectrum of essential tremor, and hence may be amenable to treatment with propranolol.