Sensory functions in dystonia: insights from behavioral studies.

The pathophysiology of primary dystonia is thought to involve dysfunction of the basal ganglia cortico-striatal-thalamo-cortical motor circuits. In the past, emphasis was placed on the role of the basal ganglia in controlling movements; in more recent times, however, it has also become clear that they play an important part in sensory as well as cognitive functions. Here, we review evidence for dysfunction of sensory processing in patients with dystonia, and speculate that this may lead to abnormalities in a crucial role of the basal ganglia that links sensory information to appropriate motor output. Sensory function, particularly in the somatosensory domain, has been shown to be compromised in patients with primary dystonia, both in adult onset focal dystonia and in genetically characterized DYT1 dystonia. Given that nonaffected DYT1 gene carriers may show similar abnormalities to clinically affected individuals, sensory deficits could constitute a subclinical endophenotypic trait of disease that precedes overt clinical manifestations. Whether they can trigger primary dystonia or are an epiphenomenon is an issue warranting further study, but the fact that a number of different neurorehabilitative approaches explicitly manipulate somatosensory inputs to improve motor function suggests there may be a causal link between them. We believe that in future, randomized, blind and controlled studies in large patient populations should address this issue, providing efficient strategies to aid functional recovery, particularly in focal hand dystonia, where the available medical treatments offer little benefit.