Autoimmune encephalitis presenting with atypical parkinsonism: A case report and review of the literature

An 81‐year‐old man developed axial rigidity, bradykinesia, and cognitive impairment within 6 weeks. On initial examination, he was misdiagnosed with progressive supranuclear palsy (PSP). Brain magnetic resonance imaging showed hyperintensities in the bilateral mesial temporal lobes and basal ganglia. Neuronal antibodies previously reported in autoimmune encephalitis mimicking PSP were negative. Immunohistochemical and immunocytochemical analysis revealed the autoantibodies recognized neuronal surface and intracellular antigens. The diagnostic criteria for probable autoimmune encephalitis were fulfilled. We diagnosed him with autoimmune encephalitis. Intravenous immunoglobulin and steroid therapy improved his symptoms. The presence of novel autoantibodies causing autoimmune encephalitis presenting with atypical parkinsonism was suggested.