Cerebrospinal fluid Aβ42, t-tau, and p-tau levels in the differential diagnosis of idiopathic normal-pressure hydrocephalus: a systematic review and meta-analysis.

OBJECTIVES: The purpose of this systematic review and meta-analysis was to evaluate the performance of cerebrospinal fluid (CSF) beta amyloid 42 (Aβ42), total tau (t-tau), and phosphorylated tau (p-tau) as potential diagnostic biomarkers for idiopathic normal-pressure hydrocephalus (iNPH) and to assess their utility indistinguishing patients with iNPH from those with Alzheimer disease (AD) and healthy normal controls.

METHODS: Studies were identified by searching PubMed, Embase, the Cochrane Library, Web of Science, Chinese National Knowledge Infrastructure (CNKI), Wanfang Chinese Periodical Database, VIP Chinese database, and Chinese Bio-medicine Database (CBM) before August 2016. The standardized mean difference (SMD) and 95% confidence interval (CI), comparing CSF Aβ42, t-tau, and p-tau levels between iNPH, AD and healthy controls, were calculated using random-effects models. Subgroup analyses were created according to ethnicity (Caucasian or Asian) and CSF type (lumbar or ventricular), and the publication bias was estimated using Egger's test and the Begg's test.

RESULTS: A total of 10 studies including 413 patients with iNPH, 186 patients with AD and 147 healthy controls were included in this systematic review and meta-analysis. The concentrations of CSF t-tau, and p-tau were significantly lower in iNPH patients compared to AD (SMD = -1.26, 95% CI -1.95 to -0.57, P = 0.0004; SMD = -1.54, 95% CI -2.34 to -0.74, P = 0.0002, respectively) and lower than healthy controls (SMD = -0.80, 95% CI -1.50 to -0.09, P = 0.03; SMD = -1.12, 95% CI -1.38 to -0.86, P < 0.00001, respectively). Patients with iNPH had significantly lower Aβ42 levels compared with controls (SMD = -1.14, 95% CI -1.74 to -0.55, P = 0.0002), and slightly higher Aβ42 levels compared with AD patients (SMD = 0.32, 95% CI 0.00-0.63, P = 0.05). Subgroup analyses showed that the outcomes may have been influenced by ethnicity and CSF source. Compared to AD, overall sensitivity in differentiating iNPH was 0.813 (95% CI 0.636-0.928) for Aβ42, 0.828 (95% CI 0.732-0.900) for t-tau, 0.943 (95% CI 0.871-0.981) for p-tau. Relative to AD, overall specificity in differentiating iNPH was 0.506 (95% CI 0.393-0.619) for Aβ42, 0.842 (95% CI 0.756-0.907) for t-tau, 0.851 (95% CI 0.767-0.914) for p-tau.

CONCLUSION: The results of our meta-analysis suggest that iNPH may be associated with significantly reduced levels of CSF Aβ42, t-tau and p-tau compared to the healthy normal state. Compared to AD, both t-tau and p-tau were significantly decreased in iNPH, but CSF Aβ42 was slightly increased. Prospective studies are needed to further assess the clinical utility of these and other CSF biomarkers in assisting in the diagnosis of iNPH and differentiating it from AD and other neurodegenerative disorders.