Quantitative assessment of mirror movements after stroke.
BACKGROUND AND PURPOSE: Mirror movements (MM) are involuntary synchronous movements of one limb during voluntary unilateral movements of the opposite limb. We measured MM in stroke and control subjects and evaluated whether MM after stroke are related to motor function. METHODS: Twenty-three patients and 16 control subjects were studied. A computerized dynamometer was used during two squeezing tasks to measure intended movements from the active hand as well as MM from the opposite hand. Motor deficits were measured with the arm motor component of the Fugl-Meyer scale. RESULTS: During paretic hand squeezing, MM in the unaffected hand were detected in 70% (repetitive squeeze) to 78% (sustained squeeze) of stroke patients. For both tasks, this was significantly (P < 0.05) greater than the incidence of MM in the paretic hand or in either hand of control subjects (17% to 44%), except when compared with the incidence of MM in the dominant hand of control subjects (56%; P = 0.17). The incidence of MM in the paretic hand was not significantly different from that seen in either hand of control subjects. Patients with MM in the unaffected hand had significantly greater motor deficit than patients without MM. Patients with MM in the paretic hand had significantly better motor function than patients without MM. CONCLUSIONS: Simultaneously recording motor performances of both hands provides precise information to characterize MM. MM in the unaffected hand and in the paretic hand are associated with different degrees of motor deficit after stroke. Evaluation of MM may be useful for studying mechanisms of stroke recovery.