Cognitive profiles in idiopathic normal pressure hydrocephalus and Alzheimer's disease
Background Idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer's disease (AD) are neurodegenerative disorders with partly overlapping clinical features. Since the treatment is different, we need better knowledge about how the cognitive profile differs between these conditions. Objective We aimed to compare the cognitive profile of iNPH patients with that of a large cohort of confirmed AD patients. Methods Patients diagnosed with iNPH and accepted for shunt surgery were compared with patients with biomarker verified Alzheimer's disease in The Norwegian Register of Persons Assessed for Cognitive symptoms (NorCog). All patients underwent a standardized cognitive assessment with age and education adjusted z-scores. We used the Clinical Dementia Rating Scale (CDR) to adjust for disease severity. Since the cognitive score distributions were highly skewed, we used nonparametric analyses stratified by CDR stage combined with multinomial logistic regression. Results In total, 276 iNPH patients were compared to 1113 AD patients. iNPH patients performed significantly poorer on phonemic fluency [median z-score difference (AD—iNPH) 0.30, 95% confidence interval (CI) 0.20 to 0.50], but significantly better on other cognitive tests, in particular immediate (median difference −0.35, 95% CI −0.49 to −0.20) and delayed recall (median difference −0.46, 95% CI −0.59 to −0.34). The differences persisted after adjustment for CDR and were most pronounced in early stages of the disease. Conclusions iNPH seems to affect phonemic fluency more and memory less than AD. As the disease progresses, the cognitive profiles become more similar, and the conditions cannot be distinguished by cognitive tests.