Brain positron emission tomography in idiopathic normal-pressure hydrocephalus: new 18F-fluorodeoxyglucose pattern in a long-known syndrome.

Abstract

Patients with idiopathic normal-pressure hydrocephalus (iNPH) can show a global reduction in cerebral glucose metabolism at [18F]Fluorodeoxyglucose (FDG) PET. The presence of caudate hypometabolism has been identified as a potential biomarker in iNPH, yet there is limited evidence of hypermetabolic findings in patients with iNPH so far. We retrieved retrospectively patients with iNPH and normal cognitive assessment, evaluated before surgery undergoing brain [18F]FDG-PET. The 18F-FDG-PET brain scans were compared to those of a control group of healthy subjects, matched for age and sex, by statistical parametric mapping (SPM) to identify areas of relative hypo- and hypermetabolism. Furthermore, the existence of a correlation between areas of hypo- and hypermetabolism in the patient group was tested. Seven iNPH patients (mean age 74 ± 6 years) were found in the hospital database. SPM group analysis revealed clusters of significant hypometabolism (P = 0.001) in the iNPH group in the dorsal striatum, involving caudate and putamen bilaterally. Clusters of significant hypermetabolism (P = 0.001) were revealed in the bilateral superior and precentral frontal gyrus (BA 4, 6). A significant inverse correlation between striatal hypometabolism and bilateral superior and precentral frontal gyrus hypermetabolism was revealed (P < 0.001 corrected for multiple comparisons). In this cohort, patients with iNPH showed subcortical hypometabolism, including bilateral dorsal striatum. To the best of our knowledge, this is the first report demonstrating a hypermetabolic pattern in the primary motor and premotor areas, and showing an inverse correlation between the striatum and motor cortex in patients with iNPH.