Mirror movements in patients with Parkinson's disease

Mirror movements (MM) refer to ipsilateral involuntary movements that appear during voluntary activity in contralateral homologous body regions. This study aimed to compare the frequency and distribution of MM in an unselected sample of 274 patients with Parkinson's disease (PD) and 100 healthy subjects, and to check a possible relationship between MM and parkinsonian features. MM of the hand were scored according to the Woods and Teuber scale. The frequency of MM was lower in PD patients than in healthy subjects (29% vs. 71%, P < 0.0001). The distribution of MM also differed in the two groups being often bilateral in healthy subjects, invariably unilateral in PD patients. When parkinsonian signs were unilateral, MM always manifested on the unaffected side; when parkinsonian signs were bilateral, MM manifested on the less affected side. PD patients manifesting MM scored significantly lower on Hohen and Yahr staging than patients without MM. Likewise, there was a significant inverse correlation between the intensity of MM as rated by the Woods and Teuber score and HY staging (r = -0.16, P < 0.01). The low frequency of MM in PD probably relates to the complex interactions between the pathophysiological mechanisms leading to parkinsonian signs and the mechanisms responsible for movement lateralization.