Alzheimer's Disease CSF Biomarker Profiles in Idiopathic Normal Pressure Hydrocephalus.

Patients with idiopathic normal pressure hydrocephalus (iNPH) frequently show pathologic CSF Aβ ₄₂ levels, comparable with Alzheimer's Disease (AD). Nevertheless, the clinical meaning of these findings has not been fully explained. We aimed to assess the role of AD CSF biomarkers (Aβ ₄₂ , Aβ ₄₂ /Aβ ₄₀ , p-tau, t-tau) in iNPH. To this purpose, we enrolled 44 patients diagnosed with iNPH and 101 with AD. All the patients underwent CSF sampling. We compared CSF biomarker levels in iNPH and AD: Aβ ₄₂ levels were not different between iNPH and AD, while Aβ ₄₂ /Aβ ₄₀ , p-tau, and t-tau were significantly different and showed excellent accuracy in distinguishing iNPH and AD. A multiple logistic regression analysis showed that Aβ ₄₂ /Aβ ₄₀ was the variable that most contributed to differentiating the two groups. Furthermore, iNPH patients with positive Aβ ₄₂ /Aβ ₄₀ had higher p-tau and t-tau than iNPH patients with negative Aβ ₄₂ /Aβ ₄₀ . Those iNPH patients who showed cognitive impairment had lower Aβ ₄₂ /Aβ ₄₀ and higher p-tau than patients without cognitive impairment. We concluded that positive CSF Aβ ₄₂ with negative Aβ ₄₂ /Aβ ₄₀ , p-tau, and t-tau is a typical CSF profile of iNPH. On the contrary, positive Aβ ₄₂ /Aβ ₄₀ in iNPH patients, especially when associated with positive p-tau, may lead to suspicion of a coexistent AD pathology.