Brain linear measurement index in the differential diagnosis between idiopathic normal pressure hydrocephalus and progressive supranuclear palsy.

Background and purpose: Differential diagnosis between idiopathic normal pressure hydrocephalus (iNPH) and progressive supranuclear palsy (PSP) could be challenging, due to the presence of similar clinical and neuroradiological features. Aim of this retrospective study was to differentiate iNPH from PSP by means of brain linear measurement (BLM) index.

Materials and methods: All the enrolled patients underwent a 1.5-T brain-MRI and BLM index was calculated on T1-weighted images. The magnetic resonance hydrocephalic index (MRHI) was also measured. For each index, receiver operating characteristic (ROC) analyses were performed to differentiate between iNPH and PSP obtaining the area under the curve (AUC), sensitivity, specificity, and accuracy values.

Results: Seventy-three patients (35 iNPH and 39 PSP) were consecutively enrolled. BLM and MRHI were significantly higher in iNPH patients than in PSP. In differentiating iNPH from PSP, the BLM index had the highest AUC (0.997) with a sensitivity of 97.1%, a specificity of 100% and an accuracy of 98.6% with an optimal cut-off value of 0.285.

Conclusion: BLM may be useful in the differential diagnosis between iNPH and PSP. At an individual level, the BLM index was the most accurate measure, representing a valid, easy and reliable tool, to achieve an accurate differentiation between these two conditions.