Exploring the Role of Cerebrospinal Fluid and Serum Mid-Regional Pro-Adrenomedullin in Tick-Borne Encephalitis: A Pilot Study

<b>Background</b>: Adrenomedullin (ADM) is a multifunctional peptide with vasoregulatory, antimicrobial, and anti-inflammatory properties. Its stable fragment, mid-regional pro-adrenomedullin (MR-proADM), is a validated biomarker in sepsis and systemic infections, but its role in viral neuroinfections remains unexplored. Tick-borne encephalitis (TBE), caused by the tick-borne encephalitis virus (TBEV), is a major viral infection of the central nervous system (CNS) associated with long-term neurological sequelae. This study aimed to assess MR-proADM levels in cerebrospinal fluid (CSF) and serum of patients with TBE and to evaluate their diagnostic utility and pathophysiological significance. <b>Methods</b>: This retrospective observational study included 20 patients with confirmed TBE and 14 non-infectious neurological controls. MR-proADM concentrations were measured in paired CSF and serum samples using an ELISA assay. Statistical analyses included group comparisons (Mann-Whitney U test), correlation analyses (Spearman's r), and receiver operating characteristic (ROC) curve evaluation. <b>Results</b>: Serum MR-proADM levels at baseline (SER1) were significantly lower in TBE patients compared with controls (<i>p</i> = 0.0197). The CSF/serum MR-proADM ratio differed significantly between groups (<i>p</i> = 0.0063) and showed the best diagnostic performance (AUC = 0.816, 95% CI 0.63-0.93; sensitivity 79%, specificity 80%). MR-proADM concentrations in CSF correlated with total CSF protein (r = 0.53), suggesting an association with blood-CSF barrier dysfunction. Strong reproducibility was observed for serum MR-proADM between sampling points (r = 0.83). <b>Conclusions</b>: MR-proADM levels in CSF and serum are altered in patients with TBE, indicating its potential as a biomarker of CNS infection and inflammation. The CSF/serum MR-proADM ratio may serve as a sensitive indicator of blood-CSF barrier involvement, while decreased serum levels may reflect impaired systemic neuroprotective response. These findings highlight a possible role of ADM in neuroimmune regulation during viral encephalitis and warrant validation in larger prospective studies.