Focal hand dystonia, mirror dystonia and motor overflow

Focal hand dystonia (FHD) is a syndrome of sustained muscle contraction, frequently causing twisting and repetitive movements or abnormal postures of the hand. Motor overflow, defined as unintentional muscle contraction that accompanies but is anatomically distinct from the primary dystonic movement, is a frequent but often unrecognized feature of FHD. In this series of eight patients with FHD, we describe two patterns of motor overflow, termed "ipsilateral overflow" and "contralateral overflow", and contrast it with the phenomenon termed "mirror dystonia". These findings extend the phenomenology and provide evidence for widespread abnormalities of motor control in patients with focal hand dystonia.