Dystonia and Tremor: The Clinical Syndromes with Isolated Tremor

Abstract

Background: Dystonia and tremor share many commonalities. Isolated tremor is part of the phenomenological spectrum of isolated dystonia and of essential tremor. The occurrence of subtle features of dystonia may allow one to differentiate dystonic tremor from essential tremor. Diagnostic uncertainty is enhanced when no features of dystonia are found in patients with a tremor syndrome, raising the question whether the observed phenomenology is an incomplete form of dystonia.

Methods: Known forms of syndromes with isolated tremor are reviewed. Diagnostic uncertainties between tremor and dystonia are put into perspective.

Results: The following isolated tremor syndromes are reviewed: essential tremor, head tremor, voice tremor, jaw tremor, and upper-limb tremor. Their varied phenomenology is analyzed and appraised in the light of a possible relationship with dystonia.

Discussion: Clinicians making a diagnosis of isolated tremor should remain vigilant for the detection of features of dystonia. This is in keeping with the recent view that isolated tremor may be an incomplete phenomenology of dystonia.

Keywords: Dystonia; dystonic disorders; essential tremor; movement disorders; tremor.

Figure 1. Tremor generation by an oscillating circuit. An oscillation may arise whenever there is a delay in a negative feedback loop or an increase in gain in the control signal. A reference signal provides input about the target or goal state; a comparator compares the sensed information and the reference signal; gain transforms comparison into a control signal (i) that brings the sensed position closer to the reference signal, thus negating the error; the plant converts control signals into real output.