A Reflection on Motor Overflow, Mirror Phenomena, Synkinesia and Entrainment

In patients with movement disorders, voluntary movements can sometimes be accompanied by unintentional muscle contractions in other body regions. In this review, we discuss clinical and pathophysiological aspects of several motor phenomena including mirror movements, dystonic overflow, synkinesia, entrainment and mirror dystonia, focusing on their similarities and differences. These phenomena share some common clinical and pathophysiological features, which often leads to confusion in their definition. However, they differ in several aspects, such as the body part showing the undesired movement, the type of this movement (identical or not to the intentional movement), the underlying neurological condition, and the role of primary motor areas, descending pathways and inhibitory circuits involved, suggesting that these are distinct phenomena. We summarize the main features of these fascinating clinical signs aiming to improve the clinical recognition and standardize the terminology in research studies. We also suggest that the term mirror dystonia may be not appropriate to describe this peculiar phenomenon which may be closer to dystonic overflow rather than to the classical mirror movements.

Automated summary

In this review, we discuss the clinical and pathophysiological aspects of various motor phenomena in patients with movement disorders. These phenomena, including mirror movements and dystonic overflow, share some similarities but also differ in terms of the body part involved, the type of movement, and the underlying neurological condition. We aim to improve the clinical recognition and standardize the terminology of these fascinating clinical signs.