Difficulties in differential diagnosis of chronic tick-borne encephalitis and progressive supranuclear palsy

The article presents two clinical cases of 51 and 57-year-old patients living in regions endemic for tick-borne encephalitis in which the differential diagnosis between progressive supranuclear palsy (PSP) and the extremely rare parkinsonian variant of chronic tick-borne encephalitis (CTBE) resulted in a diagnostic challenge. In both cases there was a clinical presentation of progressive symmetric levodopa-resistant parkinsonism with vertical gaze palsy, cognitive impairment of the executive type, frontal lobe signs, focal dystonia and in one case — early onset of postural instability, which corresponds to the diagnosis of probable PSP. The parkinsonian variant of CTBE was supported by the lack of tick-borne encephalitis virus IgG-antibodies negativity in the blood for several years, intrathecal oligoclonal antibody synthesis in one patient, the absence of typical neuroimaging signs of PSP, and delayed disease onset after a tick bite. Difficulties in diagnosis and possible mechanisms of the pathogenesis of primary progressive CTBE, as well as the similarity of the clinical and pathomorphological presentation of PSP, von Economo encephalitis lethargica, and postencephalitic parkinsonism are discussed.