# Complement Inhibition in Chronic Subdural Hematoma Fluid

## TL;DR

This study explores the role of the complement system in chronic subdural hematoma and finds evidence of complement inhibition.

## Contribution

The study is the first to investigate complement activation and inhibition in chronic subdural hematoma fluid and tissue.

## Key findings

- Clusterin levels were increased in chronic subdural hematoma fluid.
- C5a and C9 levels were decreased in chronic subdural hematoma fluid.
- C5b-C9 membrane attack complex was not detected in the CSDH membrane or dura.

## Abstract

Emerging data suggest a complex pathophysiology of chronic subdural hematoma (CSDH) to which an inflammatory response might contribute. The complement system is activated in acute traumatic setting, although its role in CSDH is unknown. To investigate the complement system in CSDH pathophysiology, we analyzed blood and hematoma fluid biomarkers, as well as immunohistochemistry of the CSDH membrane and dura.

We simultaneously collected CSDH fluid and peripheral blood from 20 CSDH patients at the time of surgery. Biopsies of the dura mater and the CSDH capsule were obtained and analyzed by immunohistochemistry for C5b-C9 or C5a deposition. Biomarkers of inflammation and complement activation were analyzed by a 21-multiplex assay, including Adiponectin, Clusterin, Complement factor C9 and CRP. Complement factor C5a was analyzed separately by a commercial R-plex electrochemiluminescence assay.

Ten biomarkers differed significantly between peripheral blood and paired CSDH of which two were significantly increased in CSDH fluid (Clusterin and Cystatin C). Eight of the significantly altered biomarkers were significantly decreased in CSDH fluid, including C5a, Complement 9 and Adiponectin. There was no immunoreactivity for C5a or the C5b-C9 membrane attack complex in the dura or CSDH membrane.

In CSDH levels of the complement inhibitor Clusterin were increased, whereas levels of C5a and C9 were decreased. Membrane attack complex C5b-C9 was not detected in the membrane or dura surrounding the CSDH. Inhibition of complement could lead to reduced clearance of debris in the CSDH as well as secondary inflammatory reactions.