RESUMO
Tick-borne encephalitis (TBE) is one of the most serious neurological tick-transmitted diseases. The initial phase usually occurs with non-specific symptoms such as fever, headache, and muscular pain. The clinical spectrum of the second phase of the disease typically ranges from mild meningitis to severe meningoencephalitis. Our case demonstrates a rare clinical case of acute myositis as manifestation of TBE virus infection. A 33-year-old female was admitted to the Rheumatology centre with a fever followed by proximal muscle pain and weakness. Despite the tick bite history and marginally positive anti-TBE virus IgM titre, the patient did not present any neurological symptoms. Laboratory test results showed elevated creatine kinase (CK) and myoglobin. Other infections, idiopathic inflammatory myopathies, were excluded. TBE virus infection was confirmed by rapid seroconversion of specific IgG class antibodies in serum. The second phase of the disease was followed by neurological symptoms and a repeated increase of CK and myoglobin. We suggest that in the case of acute myositis of unknown cause and the history of thick bite, TBE virus infection should be considered and creatine kinase might be considered as a laboratory marker of disease activity that correlates with the severity of the disease.