Comparison of Clinical, Laboratory and Immune Characteristics of the Monophasic and Biphasic Course of Tick-Borne Encephalitis.

The biphasic course of tick-borne encephalitis (TBE) is well described, but information on the monophasic course is limited. We assessed and compared the clinical presentation, laboratory findings, and immune responses in 705 adult TBE patients: 283 with monophasic and 422 with biphasic course. Patients with the monophasic course were significantly ( ≤ 0.002) older (57 vs. 50 years), more often vaccinated against TBE (7.4% vs. 0.9%), more often had comorbidities (52% vs. 37%), and were more often treated in the intensive care unit (12.4% vs. 5.2%). Multivariate logistic regression found strong association between the monophasic TBE course and previous TBE vaccination (OR = 18.45), presence of underlying illness (OR = 1.85), duration of neurologic involvement before cerebrospinal fluid (CSF) examination (OR = 1.39), and patients' age (OR = 1.02). Furthermore, patients with monophasic TBE had higher CSF levels of immune mediators associated with innate and adaptive (Th1 and B-cell) immune responses, and they had more pronounced disruption of the blood-brain barrier. However, the long-term outcome 2-7 years after TBE was comparable. In summary, the monophasic course is a frequent and distinct presentation of TBE that is associated with more difficult disease course and higher levels of inflammatory mediators in CSF than the biphasic course; however, the long-term outcome is similar.