Diagnostic accuracy of Magnetic Resonance Parkinsonism Index in differentiating progressive supranuclear palsy from Parkinson's disease and controls in Indian patients

Aims and Objectives: An assessment of the sensitivity and specificity of magnetic resonance (MR) imaging measurements of midbrain, pons, middle cerebellar peduncles (MCPs), and superior cerebellar peduncles (SCPs) and MR Parkinsonism Index (MRPI) in differentiating progressive supranuclear palsy (PSP) from Parkinson's disease (PD) and controls was performed. The correlation of these MR imaging measurements with the duration and severity of disease in the Indian patients using the PSP rating scale (PSPRS) was also performed. Materials and Methods: Twenty-six consecutive patients were enrolled in this study, satisfying the diagnostic criteria by the National Institute for Neurological Disorders and Stroke, and the Society for PSP (NINDS-SPSP), along with 13 PD and 30 control patients. All PSP patients were assessed using the PSP rating scale and staging system. Radiologists were blinded to the clinical diagnoses. MRPI was calculated by multiplying the pons area/midbrain area ratio by MCP width/SCP width ratio. The midbrain/pons area (M/P) ratio was measured as the ratio of midbrain area to pons area. Results: Mean MRPI in PSP patients (23.48 +/- 9.61) was significantly higher than that in PD patients (9.07 +/- 2.23) and controls (9.45 +/- 1.87). In this study, MRPI was 100% sensitive, specific, and accurate in differentiating PSP from PD and was 96.3% sensitive, 100% specific, and 98.21% accurate in differentiating PSP from controls. No correlation was found between the duration of disease, PSP rating scale, PSP staging system, and MRPI in the present study. MRPI was only marginally superior to the M/P ratio in differentiating between PSP and PD patients on an individual basis. No overlapping values were observed in the PSP and PD patients. Conclusion: Magnetic Resonance Parkinsonism Index is more sensitive, specific, and accurate in differentiating PSP from PD in the early stages on an individual basis.