Abstract
Background: Tick-Borne Encephalitis virus (TBEV) is a positive-sense single-stranded RNA virus belonging to the Flaviviridae family. TBEV transmission typically occurs through infected Ixodes tick bite or by consumption of unpasteurised milk from infected cattle. Case report: We report the clinical, neuroimaging, electroencephalogram (EEG), and laboratory (microbiological tests and spinal tap) data of a 6- year-old boy with Tick-borne encephalitis. Our patient presented with a biphasic course, initially with a myositis-like picture on his first admission to the emergency department, and after a few days with an encephalitic picture, resulting in a second hospitalization. EEG showed focal slow activity, while his brain magnetic resonance imaging (MRI) showed a signal abnormality, which completely resolved on repeat MRI after 3 months. Conclusion: To our knowledge, this is the youngest patient presenting with myositis in the first phase of Tick-borne encephalitis (TBE). In the presence of a biphasic clinical course, with previous myositis, aspecific MRI changes in the thalamic and midbrain regions and an EEG documenting slowed bioelectrical activity should prompt suspicion of TBEV infection.