ミトコンドリア脳筋症・乳酸アシドーシス・脳卒中様発作症候群（MELAS）の高次脳機能障害

Higher Brain Dysfunction in Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis and Stroke-Like Episodes (MELAS)

ミトコンドリア脳筋症・乳酸アシドーシス・脳卒中様発作症候群の脳卒中様病変は側頭，頭頂，後頭葉に生じることが多く，この病変分布と関連した高次脳機能障害がしばしばみられ，皮質盲をはじめ，各種の失認や失語症などが報告されている。一方，このような局所性脳病変によるもの以外に，全般性脳障害に起因するミトコンドリア認知症という病態も提唱されており，遂行機能障害をはじめとする高次脳機能障害が報告されている。

Abstract

Stroke-like episodes are one of the cardinal features of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), and occur in 84-99% of the patients. The affected areas detected on neuroimaging do not have classical vascular distribution, and involve predominantly the temporal, parietal and occipital lobes. Thus, the neurological symptoms including higher brain dysfunction correlate with this topographical distribution. In association with the occipital lobe involvement, the most frequent symptom is cortical blindness. Other symptoms have been occasionally reported in case reports: visual agnosia, prosopagnosia, cortical deafness, auditory agnosia, topographical disorientation, various types of aphasia, hemispatial neglect, and so on. On the other hand, cognitive decline associated with more diffuse brain impairment rather than with focal stroke-like lesions has been postulated. This condition is also known as mitochondrial dementia. Domains of cognitive dysfunction include abstract reasoning, verbal memory, visual memory, language (naming and fluency), executive or constructive functions, attention, and visuospatial function. Cognitive functions and intellectual abilities may decline from initially minimal cognitive impairment to dementia. To date, the neuropsychological and neurologic impairment has been reported to be associated with cerebral lactic acidosis as estimated by ventricular spectroscopic lactate levels.