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

Patients with idiopathic normal pressure hydrocephalus (iNPH) frequently show pathologic CSF Aβ42 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 (Aβ42, Aβ42/Aβ40, 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: Aβ42 levels were not different between iNPH and AD, while Aβ42/Aβ40, p-tau, and t-tau were significantly different and showed excellent accuracy in distinguishing iNPH and AD. A multiple logistic regression analysis showed that Aβ42/Aβ40 was the variable that most contributed to differentiating the two groups. Furthermore, iNPH patients with positive Aβ42/Aβ40 had higher p-tau and t-tau than iNPH patients with negative Aβ42/Aβ40. Those iNPH patients who showed cognitive impairment had lower Aβ42/Aβ40 and higher p-tau than patients without cognitive impairment. We concluded that positive CSF Aβ42 with negative Aβ42/Aβ40, p-tau, and t-tau is a typical CSF profile of iNPH. On the contrary, positive Aβ42/Aβ40 in iNPH patients, especially when associated with positive p-tau, may lead to suspicion of a coexistent AD pathology.