Lower body parkinsonism: rethinking MRI planimetry.

BACKGROUND

Magnetic resonance imaging (MRI) planimetric biomarkers such as the midbrain to pons (M/P) ratio, magnetic resonance parkinsonism index (MRPI), and MRPI 2.0 have demonstrated high diagnostic accuracy discriminating Progressive Supranuclear Palsy (PSP) patients from other atypical parkinsonisms and Parkinson's Disease (PD). However, these indexes have not been studied in the specific context of lower body parkinsonism (LBP), where the differential diagnosis between PSP, vascular parkinsonism (VP) and normal pressure hydrocephalus (NPH) is of great clinical relevance.

OBJECTIVES

Our aim was to study MRI planimetry in LBP patients, assessing its role in the differential diagnosis.

METHODS

We analyzed MRI planimetric measures, ratios and parkinsonism indexes in a retrospective sample of 71 subjects with an established clinical diagnosis: 23 of VP, 12 of NPH, 23 of PSP, compared with a group of 13 PD patients without gait or postural changes.

RESULTS

All groups with LBP-associated diagnosis showed smaller midbrain areas and wider third ventricle and frontal horns widths than the PD group. The PSP group presented the highest medians of P/M ratio, MRPI and MRPI 2.0, significantly different from all groups except NPH. The MRPI 2.0 discriminates PSP and NPH from VP patients at group level.

CONCLUSIONS

Our study found that MRPI 2.0 is able to differentiate PSP and NPH from VP at group level contributing to the differential diagnosis of LBP. Additionally, midbrain size reduction, and third ventricle and frontal horns enlargement may constitute key imaging features of LBP phenotype, including VP, NPH and PSP patients, differing from PD.