Mirror Movements in Essential Tremor: Prevalence and Relationship to Mini-Mental Status Test Scores

Background: Mirror movements (MM) are mirror reversals of contralateral, voluntary alternating or repetitive limb movements. MM have been described in age-related neurological diseases, including essential tremor (ET). MM could represent a motor release sign. Cognitive dysfunction (especially executive dysfunction) and dementia have also been reported among ET patients. It is conceivable that MM and cognitive dysfunction in ET arise from the same underlying anatomical or physiological substrate. Hence, the underlying clinical question is whether MM are a simple and easily elicited motor marker for incipient cognitive change or dementia in ET? Identifying such a marker would have value to clinicians, and we are unaware of prior studies that have assessed this issue. Methods: The Folstein Mini-Mental State Exam (FMMSE) and the Modified Mini-Mental Status Examination (mMMSE) were administered to 148 ET cases enrolled in a cross-sectional clinical study. Results: MM were present in 115 out of 148 (77.7%) ET cases. In analyses that considered age, there were no differences in FMMSE or mMMSE scores between participants with vs. without MMs (all p values >0.05). Discussion: These data suggest that MM, while present in a considerable number of ET cases, would not be a useful motor marker for incipient cognitive change in ET cases.