Patients with breakthrough tick-borne encephalitis suffer a more severe clinical course and display extensive MRI changes.

BACKGROUND: Tick-borne encephalitis (TBE) is a common viral disease in Central Europe and Asia. Severe or even lethal neurological symptoms may ensue. With limited therapeutic options, active vaccination against the TBE virus (TBEV) is strongly recommended in endemic areas. We conduct a systematic analysis of the clinical picture and cerebral imaging findings associated with TBE with particular focus on patients who acquired TBE despite of previous vaccination (vTBE). METHODS: We retrospectively describe a cohort of 52 patients with serologically proven TBE treated at our center in a 10-year-period who received at least one cerebral magnetic resonance imaging (MRI). Extension of MRI changes was systematically assessed by an experienced neuroradiologist. Standard statistic procedures were performed. RESULTS: 52 patients with a definite serological diagnosis of TBE were included. The most common presentation was encephalitis (67%). MRI showed TBE-associated parenchymal lesions in 33% of all patients. Sites of predilection included the periaqueductal gray, the thalamus, and the brainstem. 10 patients had received at least one prior active or passive TBEV-immunization. All of these had a maximal Rankin scale score of at least 4. The median number of affected anatomical regions on MRI was significantly higher than in the non-vaccinated cohort. CONCLUSIONS: To our knowledge, this is the first study systematically describing the peculiarities of MR imaging in vTBE patients. In addition to a severe clinical course, they exhibit more extensive MRI lesions than a non-vaccinated cohort. Possible reasons for these findings include incomplete seroconversion, more virulent TBEV strains or antibody-dependent enhancement.