左視床前部限局梗塞性病変における読み書き障害

READING AND WRITING DEFICIT IN CASES WITH LOCALIZED INFARCTION OF THE LEFT ANTERIOR THALAMUS

　左視床前部限局梗塞性病変により，口頭言語の障害が極く軽度であるにもかかわらず，著明な読み書き障害を呈した右利き2症例で、その読み書き障害の内容と合併症状を神経心理学的に詳細に検討し，発現機序について考察した。2症例はいずれも読み書き障害に加えて，軽度の呼称障害・記銘力障害を伴っており，X線computed tomography, magnetic resonance imagingによる病変は左視床のpolar artery・paramedian artery領域に限局していた。1例で施行したpositron emission tomography（PET）における病変は左視床以外に左頭頂葉，側頭葉に広汎に存在した。同様の視床病変を持つ過去の報告例は記銘力障害を主徴としたものがほとんどで，本症例の症状とは異なっていた。両症例の読み書き障害の発現機序として，左視床に存在する読み書き機能の一次性障害の可能性も否定はできないが，PETではじめて明示された左頭頂・側頭葉の二次性病変が症状の発現に関与している可能性が示唆された。

We have observed two cases with marked read-ing and writing deficits, in which speech and oral comprehension were generally intact. Detailed symptomatological study was performed on these cases, and the lesions were examined organically (X-ray computed tomography ＜X-ray CT＞, mag-netic resonance imaging ＜MRI＞) and functionally (positron emission tomography ＜PET＞). In addition to the marked reading and writing deficits, mild naming and memory disorders were found. X-ray CT and MRI revealed that the lesions were limitedto the regions fed by the polar and paramedian arteries in the left thalamus. In one case, PET demonstrated a functional disturbance of the left parietal and temporal lobes in addition to the left thalamus. Most previous cases have shown lesions in the anterior portion of the thalamus. It is possible that the reading and writing deficits in these cases may be due to the thalamic lesion itself, but the PET findings strongly suggest that a secondary cortical lesion may be involved in producing the higher cognitive disorders.