The Cerebral to Middle Cerebellar Peduncle Width Ratio: An Imaging Biomarker for Differentiating Multiple System Atrophy from Degenerative Parkinsonism

Introduction: The differentiation between Parkinson’s disease (PD) and atypical parkinsonian syndromes (APS) is clinically challenging. Magnetic resonance imaging (MRI) measurement of the cerebral peduncle (CP) and middle cerebellar peduncle (MCP) axial widths have not been investigated. The objective was to evaluate the utility of the CP and MCP axial widths in the differentiation of degenerative parkinsonian syndromes and their clinical correlations. Methods: The CP and MCP were retrospectively measured based on the axial T1-weighted MRI in 100 patients with probable PD, multiple system atrophy (MSA), progressive supranuclear palsy, Lewy body dementia, or Alzheimer’s disease from the movement disorders clinic at Thammasat University Hospital between January 2018 and December 2021 and in ten controls. Diagnostic accuracy was determined based on the final diagnosis. The Schwab & England activity of daily living (ADL), the Hoehn & Yahr (H&Y), and the levodopa equivalence dose (LED) were evaluated. Results: Patients with parkinsonian syndromes had smaller mean CP and MCP axial widths than controls. Patients with probable MSA had the largest axial CP widths and the smallest MCP axial widths. A CP to MCP width ratio ≥ 0.88 suggested the diagnosis of probable MSA (sensitivity 90.0%, specificity 91.2%, AUC 0.93). There was no difference in the CP width between probable PD and APS. The small CP width correlated with advanced age and poor ADL, while the small MCP width was associated with poor ADL, advanced H&Y, and low LED. Conclusion: This study shows the benefit of using CP and MCP axial widths as an imaging biomarker for patients with degenerative parkinsonian syndromes and could help differentiate MSA patients from others with parkinsonism.