Asymmetric Central Processing of Sensory Stimuli in Idiopathic Focal Dystonia

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.

Reversible reorganisation of the motor cortical representation of the hand in cervical dystonia

“…Several previous studies have demonstrated sensorimotor abnormalities in the upper limb in subjects with cervical dystonia, including inaccuracies in sensory discrimination, changes in reciprocal inhibition, abnormalities in long‐latency reflexes, and changes in regional cerebral blood flow patterns during movement 9, 21–23, 25, 28, 29. It is also recognised that patients with cervical dystonia may eventually develop dystonia outside the segment initially involved 30.…”

“…In many of the studies of focal dystonia, abnormalities were demonstrated not only in the dystonic muscles but also in clinically unaffected muscles, suggesting that there is a more widespread disorder of sensorimotor interaction in these conditions. There is evidence of cortical plasticity in the representation of upper limb muscles not directly involved in dystonic posturing in subjects with writer's cramp,19 and evidence for abnormalities in reciprocal inhibition,21, 22 sensorimotor integration,23, 24 and long latency reflexes25 in the hand and forearm in subjects with cervical dystonia.…”