Objective: To determine diagnostic accuracy of P/M, MRPI, and new indices termed P/M2.0 and MRPI2.0 (multiplying P/M and MRPI by third ventricle width/frontal horns width ratio [3^rdV/FH]) in clinically unclassifiable parkinsonism (CUP).

Background: Differential diagnosis of progressive supranuclear palsy (PSP) and multiple system atrophy (MSA) from Parkinson’s disease (PD) can be difficult especially in the early disease stages. Based on their different pattern of infratentorial atrophy, the quantitative MR planimetric measurementsMR-Parkinsonism-Index (MRPI) and pons-to-midbrain area ratio (P/M) have been reported to be abnormal in PSP, differentiating PSP from PD or MSA with high diagnostic accuracy. However, yet, few data exist on the usefulness of these MR markers for the differentiation of early stage neurodegenerative parkinsonism.

Method: MR planimetric measurements were assessed in a cohort of 84 patients with CUP. For qualification as CUP, patients had to meet at least one of the following criteria: presence of two cardinal signs of parkinsonism if the patient presented without bradykinesia; parkinsonism of mild intensity; newly diagnosed untreated parkinsonism, or disease duration of less than 18 months. Moreover, they had to fulfill step two of the UK PD Society Brain Bank Diagnostic Criteria. All patients were regularly followed-up for at least 24 months and the clinical diagnosis at last visit was considered as final diagnosis. A final diagnosis of PD required confirmation after at least 4 years. Receiver Operating Characteristic (ROC) curves statistics with their area under the curve (AUCs) were calculated for the discrimination of PSP from non-PSP.

Results: Final diagnosis in the CUP cohort after clinical follow-up was: 55 PD, 12 MSA, and 17 PSP patients. PSP patients had significant higher MRPI and MRPI2.0 as well as P/M and P/M2.0 values compared with the other groups with overlapping individual values. AUCs in discriminating PSP from non-PSP were 0.91 for both the P/M and the MRPI and 0.98 for the P/M2.0 and the MRPI2.0.

Conclusion: Brainstem-derived MR planimetric measures yield high diagnostic accuracy for the discrimination of PSP from non-PSP parkinsonism in early disease stages. Because 3^rdV enlargement is specifically involved in PSP, it seems that the inclusion of 3^rdV width makes the P/M2.0 and the MRPI2.0 more powerful in differentiating early stage PSP patients than the P/M and MRPI.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/diagnostic-accuracy-of-mr-planimetry-in-clinically-unclassifiable-parkinsonism/