BDNF and normal pressure hydrocephalus: Significant decreases in BDNF serum levels in AD and NPH patients compared to healthy controls, reflecting a lack of trophic support and progressive neurodegeneration. BDNF serum levels did not correlate with MMSE, age, and CSF levels. No significant differences in BDNF levels in CSF in AD, NPH, and controls because of its low concentration. Further investigation is needed to explain the reasons for blood BDNF level reduction between AD and NPH patients.