Abstract
Idiopathic torsion dystonia is characterized by persistent abnormalities of posture. We tested the hypothesis that abnormal sensorimotor processing is involved pathophysioiogically by looking for asymmetry of sensory processing in patients with asymmetric symptoms. Sixteen patients with torticollis (ten with head turning to the right and six to the left), seven with simple writer's cramp and 19 healthy control subjects were tested. The tasks involved matching one of five lengths of stick or weights presented to one hand with sticks and weights chosen by the other hand. All experiments were performed with the subject blindfolded. Patients with torticollis tended to underestimate weights presented to the hand away from which the head tended to turn. Control subjects showed no significant tendency to overestimate or underestimate lengths or weights with either hand, and dystonic patients showed no tendency to overestimate or underestimate lengths. Those with writer's cramp underestimated weights when the stimulus was presented to the affected hand. An asymmetry can thus be detected in muscles remote from the site of dystonia, indicating a generalized abnormality of sensorimotor processing.
Highlights
Idiopathic focal dystonia is a disorder of uncertain aetiology which is characterized by sustained, involuntary muscle contraction
Neurophysiological abnormalities have been demonstrated in dystonic patients, establishing that it has an 'organic' basis (Nakashima et aI., 1989)
Patients treated with botulinum toxin, which weakens the overactive muscles, may continue to experience abnormal head posture even when the muscles responsible for head rotation are severely weakened in comparison with their antagonists
Summary
Idiopathic focal dystonia is a disorder of uncertain aetiology which is characterized by sustained, involuntary muscle contraction. There is an increasing body of evidence that idiopathic dystonia involves a disorder of sensation. A characteristic clinical feature is the geste antagonistique, where increased somatosensory feedback, in the form of a finger placed lightly on the chin, may partially correct the dystonia in patients with torticollis. Especially painful trauma involving muscle or tendon strain rather than sharp injury, may precede the onset of dystonia (Poersch and Schlegel, 1996). Abnormalities of somatosensoryevoked potentials (Reilly et at., 1992) and regional cerebral blood flow changes in response to vibration (Tempel and Perlmutter, 1990, 1993) have been reported in dystonia. Abnormal sensory function is implicated in both the aetiology and pathophysiology of idiopathic dystonia
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