多様式失認が疑われた左視床出血の1例

Case of Left Thalamic Hemorrhage and Presumed Presence of Multimodal Agnosia

はじめに

　「失認」とは「要素的感覚，知能，注意，呼称能力，刺激に対する知識（意味記憶）」のいずれにも問題がないのに対象を認識できない障害と定義されている¹⁾．このような障害が視覚に生じた場合を視覚性失認，触覚に生じた場合を触覚性失認といい^{1, 2)}，さらに，失認が視覚と触覚の2つの感覚様式にまたがっている場合を多様式失認と呼ぶ³⁾．

　視覚情報処理経路には物体の運動や位置の認識にかかわる「背側視覚路」と，それが「何か」の認識にかかわる「腹側視覚路」があり，視覚性失認にかかわる脳領域は腹側視覚路に属する紡錘状回・海馬傍回と考えられている^{1, 3)}．触覚性失認は体性感覚情報処理の腹側路の障害で起こり，第一体性感覚野のある中心後回，第二体性感覚野のある頭頂弁蓋内側壁，下頭頂小葉などの病変により反対側の手にのみ生じる．一方，多様式失認はこの経路が視覚情報処理の腹側路と合流する左外側後頭複合やその周辺の障害で起こり，一側病変により両手に生じる³⁾．このたび，左視床出血により失語症と記憶障害，注意障害に加え，多様式失認様の症候を呈した症例のリハビリテーション治療を経験したため，報告する．

　なお，本症例報告に関して，患者本人に説明のうえ書面にて同意を得ている．

Abstract　We report a case of a 67-year-old man with left thalamic hemorrhage. He had right hemiplegia, aphasia, and higher brain dysfunction. The hemiplegia and aphasia improved with rehabilitation treatment；however, he was unable to perform activities of daily living. Visual and tactile agnosia was suspected using the visual perception test for agnosia 1 month after the hemorrhage. The patient was able to recognize common objects, such as chopsticks and a shaver, by labeling them with their names because he could read words. He was able to use these objects as a result. Multimodal agnosia with combined visual-tactile agnosia usually occurs as lesions in and around the left lateral occipital complex where the ventral stream of somatosensory information processing merges with that of visual information processing. Concurrently, the present case seems very unusual because multimodal agnosia was likely to have occurred as a lesion of the left thalamus. The compensatory strategy to put objects into words was effective in this case. We repeatedly assessed and analyzed his higher brain dysfunction in detail, which led to effective rehabilitation treatment. The present case highlights the importance of planning an appropriate treatment based on detailed evaluation and accurate diagnosis of the higher brain dysfunction in patients with neurological deficits.