Objective:  To analyze the presence of mirror movements (MM) in different extrapiramidal diseases.

Background: MM are involuntary movements that appear during voluntary activity in contralateral homologous body regions emulating the same motor task. It has been postulated that alteration or functional deficiency of motor programs and neural circuits responsible for unilateral voluntary movements, may result in motor overflow across the midline. Even though, it is known that MM could be present in neurodegenerative diseases but there are few reports of their frequency and characteristics in extrapyramidal diseases.

Methods: We conducted a descriptive transversal study in four groups of patients with different movement disorders: Parkinson Disease (PD), Ataxias, Huntington disease (HD) and Essential Tremor (ET). The assessment included a video tape of five tasks performed: finger-tapping, hand-movements, prono-supination, toe-tapping and the three-step Luria test. MM were evaluated by a movement disorders specialist using a scale previously described (Lang, 2005).

Results: Thirty three of 98 patients presented MM (34%): 16/48 of PD patients, 8/15 of HD patients, 3/8 of subjects with ET and in 6/29 of ataxic patients.

PD patients with MM had a shorter time of progression of the disease compared to the patients without MM (2.3 years vs. 12 years).

MM were observed in upper limbs in 82% and in lower limbs in 29,4%. In PD patients MM were predominant unilateral and in 81% they were present in the less affected side. Conversely, in patients with ataxia, HD and ET, MM were bilateral (100%, 71,4%, 100% respectively).

With the three-step Luria test, MM were present in 25% of PD patients, 67 % in ataxic patients, and 14% in HD patients.

Conclusions: In a previous report, our group described that MM were frequent in PD patients. This study shows similar results and reveals that MM would also be present in others movement disorders.  The presence of unilateral MM could be a semiological finding to distinguish between PD and other movement disorders.

Regarding the pathophysiology underlying MM, it was observed that the basal ganglia are reciprocally and directly connected to the contralateral motor cortex.  According to this, it would be possible that modifications of these circuits are implicated.

References: 1.Cox BC1, Cincotta M, Espay AJ.Mirror movements in movement disorders: a review.Tremor Other Hyperkinet Mov (N Y). 2012;2. pii: tre-02-59-398-1. 

2.Cincotta M1, Ziemann U.Neurophysiology of unimanual motor control and mirror movements.Clin Neurophysiol. 2008 Apr;119(4):744-62. 

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MDS Abstracts - https://www.mdsabstracts.org/abstract/mirror-movements-in-extrapiramidal-diseases/