Background: Distinguishing progressive supranuclear palsy (PSP) from Parkinson disease (PD) may be difficult, particularly in the early stages, because the characteristic vertical supranuclear eye movement abnormalities of PSP may be absent or delayed until late in the course of the disease. In this study we investigated the usefulness of comparing the square wave jerk rate (SWJR) and blink rate (BR) in the differentiation of these two disorders.
Methods: We studied 10 patients with PD (PD group) and 5 patients with PSP (PSP group) who met published diagnostic criteria. The SWJR and BR were measured from video recordings and were used to calculate a ratio (SWJR:BR).
Results: The PSP group exhibited a significantly higher SWJR, higher SWJR:BR, and lower BR than did the PD group. No patient with PSP exhibited a SWJR:BR of < 3; however, one patient with PD had a SWJR:BR of 5.3, creating overlap between the two groups.
Conclusions: The SWJR:BR is a simple and reasonably useful clinical measure to distinguish established PSP from PD. Determining the value of this measure in differentiating early PSP from PD requires a prospective study.