Challenges in Describing Tremor and Dystonia

Tremor is defined as an oscillatory and rhythmical movement. By contrast, dystonia is defined by sustained or intermittent abnormal postures, repetitive movements, or both. Tremor and dystonia often coexist in the same individual. Sometimes tremor and dystonia occur in the same body region, and sometimes they occur in separate body regions. In other cases, dystonic movements are rapid and repetitive, and they may mimic tremor. The varied clinical phenomenology of dystonia and tremor were recognized in the earliest descriptions of dystonia, and various terms have been used to describe the relationships between tremor and dystonia. The term dystonic tremor was first introduced to distinguish tremor-like movements in dystonia from more common tremors such as essential tremor. Subsequently, the same term was adopted to refer to any combination of dystonia and tremor in the same body region. Both applications of this term continue to be used in the modern literature. Other related terms have also been proposed such as tremor associated with dystonia, tremulous dystonia, dystonia-tremor syndrome, and dystonia with tremor. The proliferation of terms has become confusing, and expert opinion regarding application of these terms is divided, so a group of specialists was assembled to review the terminology and to develop recommendations for a more consistent approach. The group agreed that the term tremor should exclusively refer to rhythmic movements. The group also agreed that repetitive dystonic movements that are grossly arrhythmic should not be labeled with terms that imply they are a type of tremor. Moreover, when tremor and dystonia coexist, it may be clinically more useful to describe them separately, using descriptive terms rather than hybrid terms that imply suspected etiology. Easy-to-use clinical terms are essential, although bedside discrimination of movements may sometimes be challenging. In the future, motion analysis or physiologic measures may aid in the discrimination of movements that remain clinically uncertain.