Highly specific radiographic marker predates clinical diagnosis in progressive supranuclear palsy

The diagnosis of progressive supranuclear palsy is often challenging early in the course of the disease, when clinical signs of the condition may be less apparent and patients do not clearly meet diagnostic criteria. In this study, we examine a potential radiographic marker in progressive supranuclear palsy, and assess the timing of its presence in relation to diagnosis.

A retrospective review of patients fulfilling clinical research criteria for multiple system atrophy, Parkinson's disease, and progressive supranuclear palsy (total n = 75) was performed. Midbrain and pontine diameters, and the midbrain to pons ratio were calculated by a neuroradiologist blinded to the clinical diagnosis. The timing of the presence of a midbrain to pons ratio of less than or equal to 0.52 was assessed in the progressive supranuclear palsy group in reference to the time of diagnosis.

The midbrain to pons ratio was significantly reduced in the progressive supranuclear palsy cohort (p < 0.0001), and a midbrain to pons ratio of less than or equal to 0.52 was 100% specific for progressive supranuclear palsy. This radiologic sign predated the clinical diagnosis of progressive supranuclear palsy by a mean of 15 months (range 1-47 months) in 14 of 17 (82%) of patients in whom it was found.

The midbrain to pons ratio is an easily applied and highly specific tool in the diagnosis of progressive supranuclear palsy, and is frequently present before the diagnosis is made.