Soluble Membrane Attack Complex (sMAC) as a Potential Diagnostic Biomarker Differentiating Acute Viral Encephalitis from Guillain-Barré Syndrome, a Post-infectious Autoimmune State.

Acute encephalitis syndrome (AES) presents with the onset of fever, altered sensorium and/or seizures, known to be caused by various infectious and non-infectious aetiological agents, among which viruses are the commonest. The severity of AES prompts rapid diagnosis, which is not met by time-consuming conventional diagnostic techniques. In this study, archived cerebrospinal fluid samples of laboratory-confirmed viral AES, an acute infectious condition and Guillain-Barré Syndrome (GBS), a post-infectious, autoimmune condition was assessed for soluble membrane attack complex (sMAC) using ELISA. Statistical analysis was performed to understand the diagnostic potential of sMAC in AES versus GBS patients. sMAC levels were significantly increased in viral encephalitis compared with GBS samples (43.69 ng/mL vs. 29.33 ng/mL, P < 0.05). The diagnostic potential of sMAC was assessed using the receiver operating characteristic (ROC) curve, which demonstrated excellent diagnostic discrimination between viral AES and GBS (area under curve = 0.8125, 95% CI, P < 0.0001). Using Youden's index, the optimal sMAC cut-off was calculated as 33.6 ng/mL for distinguishing AES from GBS. The findings of our study revealed significant increase in sMAC levels in AES patients in comparison to those with GBS. This underscores the utility of sMAC as a valuable tool in distinguishing between AES and GBS, thereby facilitating more tailored patient management strategies, which varies for acute infectious and post-infectious conditions especially those mediated by autoimmunity.