特発性レム睡眠行動障害の長期経過の後に，場所依存性に幻視が出現したレビー小体型認知症の1例

Location-dependent Visual Hallucinations in a Woman with Probable Dementia with Lewy Bodies and Idiopathic Rapid Eye Movement Sleep Behavior Disorder

抄録

　約30年間の特発性レム睡眠行動障害(REM sleep behavior disorder；RBD)の経過の後に場所依存性に幻視が出現し，発症早期のレビー小体型認知症(Dementia with Lewy bodies；DLB)の診断に至った症例を経験した。本症例は50歳頃よりRBDが出現し，80歳時に軽度の記憶障害，起立性低血圧と不安定歩行を認め，83歳時に山岳部の別荘で幻視が出現した。その後，別荘を訪れるたびに幻視を認めた。都市部の自宅では，長年の主治医が他界したときにのみ幻視が出現した。本症例における幻視の発現機序には，器質要因とともに心理・環境要因が関与していると考えられた。

　We report the case of an 83-year-old Japanese woman with probable dementia with Lewy bodies (DLB), who developed location-dependent visual hallucinations (VHs) after chronic idiopathic REM sleep behavior disorder (RBD). She had developed RBD at the age of 50 years, and slight memory loss, orthostatic hypotension, and unstable gait at 81 years. At the age of 83 years, she experienced VHs in the month of March, during one of her fortnightly visits to her country cottage；she had never experienced VHs at her house in the town. The hallucinations began with her identifying a stump in the garden as a person lying on the ground, and later perceiving a tree as a hefty person. She gradually developed severe VHs such as that of 8 women hanging from a cherry tree. Finally, her condition worsened to systematic delusions；a group of peple who transforned into crows performed a religious ceremony in her garden. At her first visit to our memory clinic in the month of July, she scored 25 points on mini-mental state examination (attention 1/5；construction, 0/1). On the Bender Gestalt test, she scored 111 points, which indicated visual-perceptual disability that met the threshold score for the diagnosis of probable DLB. She, however, could describe her VHs in complete detail. MRI of the head showed mild medial temporal lobe atrophy.

　¹⁸F-FDG PET showed bilateral diffuse parieto-occipital hypometabolism. Although donepezil 5mg/day treatmet improved the status of her VH-based delusions, the frequency of RBD increased from once in a few months to every alternate day, thereby indicating a relationship between the dysfunction of cholinergic neurons and RBD. The occurrence of VHs might be due to certain environmental and psychological factors in addition to the organic brain dysfunction such as visual-perceptual disability.