[Anti-voltage-gated potassium channel (VGKC) complex/leucine-rich glioma-inactivated protein 1 (LGI1) antibody-associated limbic encephalitis mimicking dementia with Lewy bodies in a patient with subacute REM sleep behavior disorder].

A 73-year-old woman was admitted to our hospital owing to abnormal diurnal behavior, sudden brief episodes of impaired awareness, and loud nocturnal sleep talking. Her symptoms had developed gradually over several months and had been treated as dementia with Lewy bodies (DLB) at another clinic. Video-polysomnography revealed brief sleep talking and gross movements associated with REM sleep without atonia. 18F-FDG PET revealed increased glucose metabolism in both medial temporal lobes. These findings led to a diagnosis of limbic encephalitis (LE) comorbid with REM sleep behavior disorder (RBD). After two courses of intravenous methylprednisolone pulse therapy, her symptoms gradually improved. Her illness was later confirmed as anti-voltage-gated potassium channel (VGKC) complex/leucine-rich glioma-inactivated protein 1 (LGI1) antibody-associated LE using serum analyses. Clinical features of anti-VGKC complex/LGI1 antibody-associated LE can mimic those of DLB, particularly when comorbid with RBD.