Mirror movements or functional tremor masking organic tremor

BACKGROUND: Functional tremors can be diagnosed based on clinical and physiologic criteria such as entrainment, suggestibility, distractibility, variable nature with the associated clinical history of psychosomatic co-morbidities. The current case report highlights the underrecognized utility of neurophysiology in the correct diagnosis of tremors, providing useful clinical and neurophysiologic insights into clinical and physiological assessment of tremors. CASE REPORT: A 62-year-old woman with a past medical history of polio was referred by a movement disorders neurologist for evaluation of tremor with concerns of a likely functional etiology. On first assessment there were findings notable for a possible organic etiology, but upon subsequent evaluation the tremor was noted to be variable and entrainable, suggestive of a functional etiology. Neurophysiological tremor study could identify an underlying organic tremor (likely of multi-factorial etiology). Tremor entrainment with contralateral hand tapping could be mirror movements or functional movements, as the underlying organic tremor was not entrained. The amplitude of mirrored movement was commensurate with the tapping amplitude. DISCUSSION: Functional tremors may mask an underlying organic tremor. Additionally, motor overflow which may happen especially with large amplitude movements may masquerade as mirror movements, which can be difficult to differentiate from an entrained functional tremor. Objective physiology and refinement of the current clinical and physiologic tremor evaluation techniques may help identify an underlying organic etiology.