Brain linear measurements for differentiating normal pressure hydrocephalus from Alzheimer's disease: an exploratory study

Abstract Background and purpose Easy and reliable tools for the differential diagnosis between idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer's disease (AD) are needed. Materials and methods In this cross‐sectional study iNPH and AD patients referred to the Neurology Unit of the University of Catania from 1 January 2020 to 1 December 2022 were enrolled. The following brain linear measurements (BLMs) were calculated: Evan's index (EI), the parieto‐occipital ratio (POR) and the temporal ratio (TR). For each index, sensitivity, specificity and the area under the curve (AUC) were calculated. Moreover, a cumulative index, the BLM index, was also considered. Results Fifty patients (25 iNPH and 25 AD) were enrolled. In differentiating iNPH from AD, EI had the highest AUC (0.956), POR had the highest specificity (100%) whilst TR had the highest sensitivity (92%). The BLM index differentiated iNPH and AD with a sensitivity of 96%, a specificity of 92% and an AUC of 0.963 with an optimal cut‐off value of 0.303. Conclusion Evan's index, POR and TR may be useful in the differential diagnosis between iNPH and AD. At an individual level, the BLM index represents a valid and reliable tool to achieve an accurate differentiation between these two conditions.