LAUSR

We thank Ugga and colleagues for their interest and positive comments on our recent article. We agree that differentiating between idiopathic normal pressure hydrocephalus (iNPH) and progressive supranuclear palsy (PSP) is often challenging and that simple imaging biomarkers are needed for the differential diagnosis between these two diseases in clinical practice. The Magnetic Resonance Parkinsonism Index (MRPI) and its new version, including also the measurement of the third ventricle width (MRPI 2.0), are well known and accurate biomarkers to distinguish PSP from other degenerative parkinsonism. However, as demonstrated in our article and discussed by Ugga et al, these biomarkers were not able to differentiate PSP from iNPH because of the overlap of some radiological features between these diseases. In our recent article published in Movement Disorders, we proposed a new imaging linear biomarker, termed Magnetic Resonance Hydrocephalic Index (MRHI), which showed very high accuracy in differentiating iNPH from PSP. In our article, we also validated the performance of MRHI in a training and a testing cohort obtaining similar accuracy values, thus demonstrating the potential usefulness of this biomarker also in patients from new sites. Ugga et al investigated the potential role of the interpeduncular angle (IPA), which showed higher divarication of the cerebral peduncles in iNPH compared to PSP patients. The IPA values were significantly higher in iNPH with respect to PSP but showed some overlap between the 2 patient groups. Thus, we retain that the IPA could be a promising new biomarker, but further studies are needed to evaluate and validate its accuracy in differentiating iNPH from PSP. Finally, we agree on the use of imaging biomarkers in the differential diagnosis between iNPH and PSP to reduce misdiagnosis and avoid ineffective shunt procedures.