Square wave jerks in parkinsonian syndromes.

The frequency of square wave jerks (SWJ) was compared in eight patients with progressive supranuclear palsy (PSP), 25 patients with multiple system atrophy or Parkinson's disease plus (MSA/PP), 85 patients with idiopathic Parkinson's disease (PD) and 20 age-matched normal volunteers. In the control group, the mean (SD) SWJ frequency (SWJ larger than 1 degree amplitude) was 2.3 (2.4)/min. Abnormal ocular fixation (SWJ frequency greater than 10/min) was observed in a large proportion of PSP patients (7/8) and of MSA/PP patients (16/25) but in few PD patients (13/85). In the group of PD patients with abnormal ocular fixation, freezing of gait, falls and instability were more severe than in the group of PD patients with normal fixation. The study of ocular fixation may help to differentiate PD clinically from other Parkinsonian syndromes. SWJ are probably not related to the central degeneration of the dopaminergic nigrostriatal pathway observed in PD.