Association between ventricular CSF biomarkers and outcome after shunt surgery in idiopathic normal pressure hydrocephalus

Introduction: The relationship between neurochemical changes and outcome after shunt surgery in idiopathic normal pressure hydrocephalus (iNPH), a treatable dementia and gait disorder, is unclear. We used baseline ventricular CSF to explore associations to outcome, after shunting, of biomarkers selected to reflect a range of pathophysiological processes. Methods: In 119 consecutive patients with iNPH, the iNPH scale was used before and after shunt surgery to quantify outcome. Ventricular CSF was collected perioperatively and analyzed for biomarkers of astrogliosis, axonal, amyloid and tau pathology, and synaptic dysfunction: glial fibrillary acidic protein (GFAP), chitinase-3-like protein 1 (YKL40/CHI3L1), monocyte chemoattractant protein-1 (MCP-1) neurofilament light (NfL), amyloid beta 38 (A beta 38), A beta 40, A beta 42, amyloid beta 42/40 ratio (A beta 42/40), soluble amyloid precursor protein alfa (sAPP alpha), sAPP beta, total tau (T-tau), phosphorylated tau (P-tau), growth-associated protein 43 (GAP43), and neurogranin. Results: The neurogranin concentration was higher in improved (68%) compared to unimproved patients (median 365 ng/L (IQR 186-544) vs 330 (205-456); p = 0.046). A linear regression model controlled for age, sex and vascular risk factors including neurogranin, T-tau, and GFAP, resulted in adjusted R2 = 0.06, p = 0.047. The A beta 42/40 ratio was bimodally distributed across all samples, as well as in the subgroups of improved and unimproved patients but did not contribute to outcome prediction. The preoperative MMSE score was lower within the low A beta ratio group (median 25, IQR 23-28) compared to the high subgroup (26, 24-29) (p = 0.028). The T-Tau x A beta 40/42 ratio and P-tau x A beta 40/42 ratio did not contribute to shunt response prediction. The prevalence of vascular risk factors did not affect shunt response. Discussion: A higher preoperative ventricular CSF level of neurogranin, which is a postsynaptic marker, may signal a favorable postoperative outcome. Concentrations of a panel of ventricular CSF biomarkers explained only 6% of the variability in outcome. Evidence of amyloid or tau pathology did not affect the outcome