A tremor that sometimes accompanies laryngeal dystonia and its effects on voice function (spasmodic dysphonia), breathing function (respiratory dystonia), or both. This dystonic tremor is heard as a “wavering” in the voice (if the person has spasmodic dysphonia) or in the sound of inhaled or exhaled air (if the person has respiratory dystonia), or it can be detected in both the voice and the sound of inhaled or exhaled air (if the person has both spasmodic dysphonia and respiratory dystonia). A patient who exhibits this kind of tremor in tandem with spasmodic dysphonia, for example, may be described by the examining clinician as having “spasmodic dysphonia with a small/moderate/large/overwhelming tremor component.” Dystonic tremor can also appear in other parts of the body (e.g., as head or limb movements) when a person’s dystonia affects those parts, but our focus here is on dystonia of the larynx.
Voice-affecting dystonic tremor might sometimes be mistaken for the tremor induced by a different neurological disorder, essential voice tremor. If one knows what to listen for, however, it is usually possible to distinguish dystonic tremor from the tremor induced by essential voice tremor. Most obviously, dystonic tremor is almost always accompanied by other manifestations of dystonia, such as phonatory arrests, dropouts to a whisper, or squeezedowns. Dystonic tremor may worsen under specific circumstances—with stress, fatigue, or during telephone use, for example. Dystonic tremor is often (though not always) more pronounced in the patient’s chest register voice than falsetto register voice—sometimes dramatically so—and this difference might be heard when the patient is asked to sustain a single sung note as steadily as possible. Finally, dystonic tremor’s amplitude can vary from cycle to cycle; to use singers’ parlance, it is as though a couple of cycles of “wild” vibrato are followed by a few cycles of merely wide vibrato, followed by a second or two of much more stable voice. In the occasional case, however, a patient’s tremor is so overwhelming and these distinctive qualities of dystonic tremor so subtle that the clinician proceeds initially with a working, rather than settled, diagnosis.