Objective: To evaluate the sensitivity and specificity of a radiographic marker, midbrain to pons ratio, in brain MRI of Progressive Supranuclear Palsy (PSP) patients as evaluated by different medical specialists.

Background: PSP can be clinically challenging to diagnose early in the disease. Recent investigations show that radiographic markers may aid in the diagnoses; one marker of interest is the midbrain to pons ratio on brain MRI and its sensitivity and specificity in PSP. One study has demonstrated that in a clinically and pathologically confirmed PSP cohort a midbrain to pons ratio of less than 0.52 was 100% specific and 85.7% sensitive for PSP.¹ This ratio is a simple marker that is calculated from midsagittal brain MRI. Application of this tool in clinic may be useful; however variability of measurements amongst different medical specialists may affect the usefulness of this marker.

Methods: A clinically confirmed cohort of age and gender matched PSP and Parkinson’s disease (PD) patients who had brain MRI with midsagittal images was selected from the University of Kansas Medical Center’s movement Disorder database. Measurements obtained included the midbrain and pons short axis diameter. The midbrain to pons ratio was calculated by dividing the midbrain to pons measurements. The measurements were obtained by a neuroradiologist and a senior neurology resident. Both raters were blinded to clinical information.

Results: Twelve PSP patients with a mean age of 69 years on date of MRI (range 64-77) and 12 PD patients with a mean age of 70 years on date of MRI (range 63-76) were evaluated. Each group was comprised of 83% males. When measured by the neuroradiologist, 12 of 12 PSP patients had a midbrain to pons ratio of less than 0.52, and 2 of 12 PD patients were also measured to be in the PSP range. This resulted in 100% sensitivity and 83% specificity. When measured by the senior neurology resident, 10 of 12 PSP patients had a midbrain to pons ratio of less than 0.52, and 2 of 12 PD patients were also measured to be in the PSP range. This resulted in a lower sensitivity than the neuroradiologist at 83% but the same specificity as the neuroradiologist at 83% for PSP.

Conclusions: The midbrain to pons ratio as a radiological marker may aid in the diagnosis of PSP. It appears that this is a sensitive and specific measure whether calculated by a neuroradiologist or a senior neurology resident.

References: The midbrain to pons ratio: A simple and specific MRI sign of progressive supranuclear palsy. Massey, L, et al. Neurology. May 14, 2013, 80:20 1856-1861.

Highly specific radiographic marker predates clinical diagnosis in progressive supranuclear palsy. Owens, E, et al. Parkinsonism and Related Disorders. May 2, 2016. 28.107-111.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/evaluation-of-a-radiographic-marker-as-a-diagnostic-tool-for-progressive-supranuclear-palsy/