音韻失読・音韻失書を呈した1例—語の音読と書き取りにおける障害の機序

Demonstration of phonological dyslexia and dysgraphia in Japanese: A case report

　本研究では，音韻失読・失書と考えられた患者に，①仮名1文字の音読および書き取り課題，②実在語・非語の仮名音読および書き取り検査，③文字を使わない音韻操作課題(モーラ抽出能力検査，実在語・非語の復唱および逆唱)，④言語性短期記憶の評価(数唱，標準言語対連合学習検査)を行い，音韻失読・失書の機序を考察した．①仮名1文字の音読および書き取り課題の正答率はいずれも約9割であり，軽度の文字-音素変換規則の障害が示唆された．②実在語に比し非語の音読および書き取りはいずれも不良であり，音韻失読・失書を認めた．③モーラ抽出能力検査の成績は良好であったが，非語の復唱，実在語および非語の逆唱成績は不良であり，著明な音韻操作障害を認めた．④数唱は低下していたが，標準言語性対連合学習検査の結果は良好であった．以上より，本例の音韻失読・音韻失書は，主に読み書きに限定されない音韻操作障害によって生じた可能性が示唆された．

　We report on a 13-year-old female Japanese patient with phonological dyslexia and dysgraphia secondary to intracranial hemorrhage and discuss the underlying mechanisms of the non-word specific reading/writing disturbances. The patient demonstrated mild anomic aphasia and writing impairment of kana (Japanese phonogram) on a comprehensive language examination given 40 days after onset. A detailed neuropsychological assessment was performed on her reading and writing performance: 1) reading and writing to dictation of basic kana characters, 2) reading and writing to dictation of words and non-words, 3) a set of phonological manipulation tasks not involving reading or writing, and 4) verbal short-term memory tasks. The patient showed 1) mild impairment in reading and writing to dictation of kana characters, suggesting a mild impairment of her phoneme-grapheme correspondence system; 2) normal writing performance of words while impaired reading and writing of non-words, indicating phonological dyslexia and dysgraphia; 3) good performance in mora segmentation tasks while significant decline in non-word repetition and mora reversal tasks; 4) limited digit span while normal performance in verbal paired-associate learning. The above-mentioned findings suggest that phonological dyslexia and dysgraphia found in this patient may have been caused by phonological disorders not limited to writing and reading functions.