Midbrain Pons Ratio- A Diagnostic Tool for Progressive Supranuclear Palsy

Abstract

Introduction: Progressive Supranuclear Palsy (PSP) is a Parkinsonism plus syndrome. PSP has different clinical features, it is unresponsive to levodopa and have poor prognosis compared to classical Parkinson’s Disease (PD). However, in clinical practice accurate diagnosis of parkinsonian syndromes are difficult especially when the patient presents early during the course of illness. Diagnosis of each condition is important since it affects patient’s management, rehabilitation and prognosis. Magnetic Resonance Imaging (MRI) is especially useful tool in parkinsonian syndromes, since it identifies changes produced by the neurodegeneration. Rostral midbrain atrophy is seen in PSP. Midbrain pons ratio helps to identify the atrophy involving midbrain, thus helps in differentiating PSP from other causes of parkinsonism. Aim: To investigate the utility of midbrain diameter and midbrain pons ratio in mid-sagittal sections of MRI for differentiation of PSP from other neurodegenerative parkinsonism. Materials and Methods: This was a cross-sectional study conducted in Department of Neurology, Government Medical College, Kottayam, Kerala, India. Of all the patients who presented with clinical features of Parkinsonism, 124 patients who met the inclusion criteria were selected for the study. Comparison was made between the values obtained in clinically diagnosed patients with PSP (n=30), PD (n=30), Multiple System Atrophy (MSA) (n=30), Corticobasal Degeneration (CBD) (n=4) and normal Controls (n=30). These patients underwent MRI and the mid-sagittal T1 weighted MRI images were obtained; the diameter of midbrain and pontine base as well as midbrain-topons ratio was calculated. Quantitative analysis of five groups were done using Analysis of Variance (ANOVA) with post-hoc Tukey correction. Results: Mean age of patients in PSP was 59.47±3.86 years. The mean midbrain diameter was found to be lower in PSP, measuring 7.8±0.83 mm (p<0.001) with reduction of the midbrain-to-pons ratio. The mean midbrain pons ratio was found to be lower in PSP, measuring 0.45±0.03 in comparison with the other parkinsonian syndromes (p<0.001). Conclusion: Midbrain pons ratio and midbrain diameter in MRI is a simple measurement for differentiating PSP from other degenerative parkinsonian syndromes.

Keywords

• midbrain diameter
• parkinson plus syndrome
• pontine diameter