Serum substance P as a predictor of outcome in patients with severe traumatic brain injury

Abstract

Introduction Substance P (SP) is a member of the tachykinin family of neuropeptides, which are widely distributed throughout the central nervous system. SP is released early following acute injury to the central nervous system, stimulating a neurogenic inflammatory response in the form of ineased permeability of the blood–brain barrier and the development of vasogenic edema. The main goal of the present study was to determine the relation between serum SP levels and the outcome in patients with severe traumatic brain injury (TBI). Patients and methods This observational, prospective study was carried out on 40 adult patients of both sexes who were admitted to the units of the itical Care Medicine Department in Alexandria Main University Hospital with Glasgow Coma Scale scores less than or equal to 8. Patients with an Injury Severity Score more than or equal to 10 in nonanial aspects were excluded. Blood samples were collected on day 1 of TBI to measure serum SP levels. The endpoint was a 28-day functional outcome. Results We found significantly higher serum SP levels ( P =0.001) in patients with the unfavorable outcomes; these included 26 patients with Glasgow Outcome Scale of 1 (death), 2 (vegetative state), and 3 (severe disability) than in patients with favorable outcome; these included 14 patients with Glasgow Outcome Scale of 4 (moderate disability) and 5 (good recovery). The area under the curve for serum SP levels with regard to predicting 28-day functional outcome was 0.827 ( P =0.001), and the best prognostic cut-off point for serum SP on admission was 167 pg/ml; at this level, sensitivity and specificity were 92.31 and 57.41%, respectively, with 80% positive predictive value and 80% negative predictive value. Conclusion SP is a promising serum biomarker that can predict functional outcomes after severe TBI. These results may help to clarify if reducing SP levels may lead to better treatment of patients with severe TBI.