Cerebrospinal fluid findings and their temporal pattern in patients with different clinical presentations of tick-borne encephalitis

Objectives: There is a lack of systematic data on cerebrospinal fluid (CSF) findings in the different clinical manifestations of tick-borne encephalitis (TBE) and according to the duration of neurological involvement. This study aims to evaluate and compare routine CSF parameters in TBE patients presenting with meningitis, meningoencephalitis, or meningoencephalomyelitis, and to assess temporal changes in CSF during the first 10 days after the onset of neurological symptoms. Methods: We analysed 15 CSF parameters in 717 consecutive adult patients hospitalized for TBE at the Department of Infectious Diseases, University Medical Centre Ljubljana, Slovenia. Among these patients, 230 (32%) had meningitis, 446 (62%) meningoencephalitis, and 41 (6%) meningoencephalomyelitis. Results: CSF findings differed significantly among the three clinical presentations. Leukocyte count, neutrophil proportion, protein levels, immunoglobulin concentrations (IgM, IgG, IgA), and intrathecal synthesis quotients were highest in meningoencephalomyelitis and lowest in meningitis. These differences remained largely significant after adjusting for confounding factors. CSF abnormalities were detectable from day one of neurological symptoms, peaked around days 4–5, and then stabilized or showed mild improvement. Neutrophils predominated during the first two days, followed by a predominance of lymphocytes and monocytes from day 3 onward. This pattern was consistent in meningitis and meningoencephalitis but less pronounced in meningoencephalomyelitis. Conclusions: Clinical manifestations of TBE exhibit distinct CSF profiles. Abnormalities are most pronounced in meningoencephalomyelitis and least in meningitis. These alterations appear early, peak within the first days, and then stabilize or improve, although this pattern is less predictable in meningoencephalomyelitis.