非典型的な特徴を呈した純粋失読の1症例の報告とその色彩呼称障害について

A CASE OF PURE ALEXIA WITH ATYPICAL,CLINICAL FEATURES, WITH SPECIAL REFERENCE TO ITS COLOR IDENTIFICATION DEFECT

I．はじめに

　純粋失読は，幾つかの特徴的臨床所見を示す症候群である。すなわち自発書字や書取りによる書字はよく保持されているのに対して，字を読むことが著しく障害され，さらにこの失読症状は文字をなぞることによつていわゆるSchreibendes Lesenによつて改善する。自発書字が良好なのに対して写字はのろく拙劣である。また多くの場合同名半盲，色彩呼称障害を伴う。今回，われわれはこれに対して非典型的特徴を示した1症例を経験したのでここに報告する。

A case of pure alexia with atypical features was reported. A 70 year-old right handed male de-veloped right homonymous hemianopsia. A leftoccipital low density area was confirmed by CT scan at that time. Eight months later, he found himself unable to read a newspaper and was admitted to the Hyogo Prefectural Awaji Hospital.

A small right homonymous scotoma was the only physical abnormality found in the neuro-logical examination.

Neuropsychological examination revealed several interesting features. His reading ability of characters and words were impaired regardless of Kanji (ideograms) or Kana (phonograms). A tendency was noted that Kanji reading became more difficult as the complexity of graphem in-creased. Of special interest was his inability to take advantage of kinesthetic cuing. He had no difficulty in copying characters. He wrote without hesitancy with good penmanship. However, Kana was the only type of characters he employed in writing.

Studies of color identification showed definite impairment of color naming and pointing to audi-torily presented color names. In addition he sometimes employed roundabout expressions in naming colors of verbally presented objects. But he was perfectly correct in matching colors of two 12 card groups with different saturation and brightness. He was able to classify 24 color cards into 6 groups in an orderly fashion according to hue. Ishihara test was also normal. Thus this patient's behavior to colors must have resulted from underlying pathology which disconnected normal color percept from color names. The result of verbal-verbal task suggested a possibility of co-existing disturbance of inner speech.

Classical theory of alexia without agraphia maintains that alexia is a result of isolation of the intact right occipital lobe from the intact left hemisphere region. This isolation is realized by the destruction of the left occipital visual region and the splenium of the corpus callosum. The former pathology is reflected clinically as the presence of the right homonymous hemianopsia. The intactness of the left speech region, especially visual speech region of the angular gyrus. is re-flected clinically as preserved ability of Schreibendes Lesen. However, the present case had disturbed Schreibendes Lesen and no conspicuous right homonymous hemianopsia. Thus there is a possi-bility that the responsible lesion in this case must be outside the classical distribution, yet maintaining the essential disconnection mechanism as demon-strated by his defective pattern of color identifi-cation.