Objective: The midbrain-to-pons ratio (MTPR) is considered as an important diagnostic biomarker to differentiate between progressive supranuclear palsy (PSP) and idiopathic Parkinson’s disease (IPD). Here, we evaluated the diagnostic value of the relative decline in MTPR over a period of one year.

Background: The differential diagnosis of PSP and IPD is still primarily based on disease-specific symptoms, which may not have fully developed at early stages of the disease. A substantial overlap of symptoms and a more rapid disease progression in PSP underline the clinical need for objective biomarkers, which enable an early and reliable differentiation. Midbrain atrophy is a hallmark of PSP and can be quantified by the MTPR. For this reason, the MTPR has been suggested to support the differentiation between PSP and IPD.

Method: Prospectively obtained midsagittal T1-weighted individual MRIs of 30 patients with PSP (n = 15) and IPD (n = 15) as well as 15 healthy controls (HC) were analysed in order to calculate the MTPR at baseline and after one year. Additionally, ROC curve analyses were performed to evaluate the predictive value of the MTPR and its relative annual decline for diagnosing PSP.

Results: In PSP, the mean MTPR at baseline was 0.45, which was significantly lower than in all non-PSP participants (mean MTPR = 0.62; F(2,42) = 59.32, p < 0.001). This was particularly driven by a smaller midbrain width in PSP, compared to IPD and HC (F(2,42) = 53.06, p < 0.001). Additionally, patients with PSP revealed a higher rate of midbrain atrophy represented by a more pronounced relative decrease in MTPR within one year as compared to IPD patients (χ2 = 13.53, p < 0.001, df = 2). ROC curve analysis confirmed excellent diagnostic accuracy for the MTPR at baseline (AUC = 0.97, cut-off ≤ 0.54; sensitivity = 0.933; specificity = 0.97; accuracy = 0,956) and good diagnostic accuracy for its relative decline (AUC = 0.85, cut-off ≥ 0.015; sensitivity = 0.733; specificity = 0.800; accuracy = 0.767).

Conclusion: We replicated previous findings confirming that the MTPR constitutes a useful estimate of midbrain atrophy, which is specifically related to PSP. Moreover, the present work evidences that the relative decline in MTPR can support MRI-based differential diagnosis: In the current sample, an annual decline ≥ 1.45% is predictive of PSP with an accuracy of 76.7%.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/decline-in-the-midbrain-to-pons-ratio-over-one-year-can-support-the-differentiation-between-psp-and-ipd/