Aim: The clinical guidelines for idiopathic normal pressure hydrocephalus (iNPH) in Japan recommend cerebrospinal fluid (CSF) drainage. The positive response rate of the diagnostic CSF drainage is not very high because brain MRI findings of Alzheimer disease (AD) are similar to those of iNPH. Therefore, we sought to determine simple, quantitative indexes of head MRI to differentiate iNPH from AD and to predict positive response of the CSF drainage in possible iNPH.
Methods: Eighteen patients with the clinical criteria of possible iNPH who had undergone diagnostic CSF drainage were evaluated. Nineteen patients with the clinical criteria of probable AD were used as controls. VSRAD, Evans index, and previously reported indicators were measured on brain MRI in all patients. These parameters were compared between AD and iNPH, and between iNPH responders and non-responders.
Results: VSRAD, Evans index, bifrontal index, width and height of the temporal horn, and the maximum height of the Sylvian fissure were higher in iNPH than AD. The cutoff value of the bifrontal index, width and height of the temporal horn, and maximum height of the Sylvian fissure were 0.31, 6.0 mm, 3.13 mm, and 7.6 mm, respectively. The minimum thickness of the medial temporal lobe was higher in the CSF drainage responders than the non-responders. The cutoff value of the minimum thickness of the medial temporal lobe was 11.0 mm.
Conclusions: Our results suggest that simple image indexes of brain MRI could distinguish iNPH from AD and predict positive response to CSF drainage in iNPH.