'Pugnatron'-like reaction in a patient with familial dystonia: torque induced motion analysis.

A patient is described who suffered from an unusual extrapyramidal syndrome involving both legs and one arm. In the affected parts there was an extreme degree of rigidity. Measurements have been made of the motion that occurred as a result of applying force to the left foot. The torque was provided by a printed motor. The effect of a maintained plantar flexing force was anomalous for the foot moved to a dorsiflexed position. A model illustrating possible principles of feedback control-the Pugnatron-is described.