左手の失書—その特徴と発現機序

LEFT UNILATERAL AGRAPHIA:ITS CHARACTERISTICS AND DYNAMICS

　抄録　前額断CTによって左側脳梁幹に病変を有することが確認された前大脳動脈梗塞例において，左手の失行，左手の失書などが認められた。とりわけ左手の失書の特徴とその発現機序について検索し，次のような結果を得た。本例の左手の失書の特徴として，（1）多産的productive，（2）新字造作的neographic，（3）反覆的iterativeな傾向が認められ，さらに，注目すべきこととして左手書字の間，完全たな絨黙状態が認められた。本例は左手の失行を伴っていたが，左手の失書は失行性とは言えず（とりわけ模写が良好），さりとて通常の意味では失語性とも言えず（右手では失書を認めない），第3の失書として独立せしめられるべきではないかと考えられた。また，もし左手書字の間の絨黙を一過性の"失語"（左半球の機能的低下を指す）であるとみなしうるならば，一過性に右半球の過活動状態が惹起される可能性があり，さらに部分的脳梁離断による左半球からの言語学的情報不足と一過性の言語学的病態失認の要因が加わることにより，上述の左手の失書の特徴の発現の説明が可能になるように思われた。

We observed 62 y. o. right-handed woman, whose truncus of corps collosum was damaged by infarc-tion of left anterior cerebral artery, that was verified by coronal CT scan finding. She was apraxic and agraphic only with left hand. We examined the characteristics of her unilateral left agraphia from the point of quantitative and qual-itative views. These analysis seemed to reveal three main characteristics of unilateral left agra-phia of this patient. These were as follows ; 1) productive, 2) neographic and 3) iterative.

Another important feature of this patient was the mute state during her left-hand writing.

Her left agraphia could not explained by apraxic factor, because her copying capacity was remar-cably preserved in comparison with her dictation or written naming ability. Furthermore, this agraphia was not aphasic because her right-hand writing was almost intact. We agreed with Yama-dori who insisted that this type of agraphia was neither apraxic nor aphasic, but the particular third agraphia which was named as "disconnection agraphia".

We considered that the mute state during her left-hand writing might some kind of transient aphasia, which may reflect the functional disturb-ance of left hemisphere, and the reduced energy in the left hemisphere could increase the activity of right hemisphere. Partial interhemispheric disconnection might induce transient "linguistic anosognosia" in this patient. We believe that these transient hyperactivity and transient linguistic anosognosia could generate above mentioned cha-racteristics of her left agraphia ; productive, neographic and iterative.