Focal hand dystonia in a patient with thoracic outlet syndrome.

A patient affected by thoracic outlet syndrome, with an involvement of the left lower primary trunk due to a rudimentary cervical rib, developed a severe hand dystonia on the same side. The dystonic posture was characterised by a flexion of the wrist with the fingers curled into the palm. Polygraphic recordings performed on the left flexor digitorum superficialis (FDS4) and extensor digitorum superficialis (EDC4) muscles, during a repetitive tapping task of the fourth digit, showed a loss of well formed bursts without a clear silent period along with long duration bursts of cocontraction in antagonistic muscles. The study of reciprocal inhibition between forearm flexor and extensor muscles showed a reduced amount of inhibition in both the disynaptic and the later presynaptic phase of inhibition. The patient underwent an operation with resection of the cervical rib. Twelve hours after the operation the patient experienced a significant improvement of the hand dystonia; the distonia had disappeared completely by two months with a progressive normalisation of reciprocal inhibition.