Unilateral monoataxiaを呈した中心前・後回小梗塞の2症例

Cerebral Small Infarcts of the Precentral and Postcentral Gyri Presenting with Unilateral Monoataxia : A Report of Two Cases

要旨　中心前・後回皮質および皮質下白質の小梗塞によりunilateral monoataxia（一側上肢の運動失調）を呈した2症例を報告した。2例とも突然発症した左上肢の小脳性運動失調症を認めたが，筋力低下，筋トーヌス異常，感覚障害はみられなかった。MRIにて症例1，2にはともに中心前回から中心後回移行部に共通した病巣を認め，症例1はさらにprecentral knob（中心前回の中心溝に突出した部分）内側部，中心前・後回皮質下白質の半卵円中心にも梗塞巣が認められた。Ataxic hemiparesisを呈した症例や動物実験の知見から，本症例の運動失調症候は大脳皮質，皮質下白質レベルでの皮質橋路または小脳皮質路障害，中心前・後回および頭頂葉の皮質間線維病変による小脳機能障害， 感覚・運動系の統合障害などが原因と考えられた。症例1，2では症状の回復に差異が認められ，発症機序の違いによると推測された。Unilateral monoataxiaの既報告例の病巣も様々であり，複数の発症機序が考えられ，病変部位により機能的予後も異なる可能性が示唆された。

Two cases of unilateral monoataxia, due to small infarcts in the precentral and postcentral gyri, were reported. A 76-year-old man（case 1）, and a 90-year-old woman（case 2）suddenly developed clumsiness of the left upper extremity. Neurological examination revealed cerebellar ataxia in the left upper extremity in both cases. But, the other abnormal neurological findings, including the muscle weakness, abnormal muscle tone, and proprioceptive deficit, were not noted. In case 2, cerebellar ataxia disappeared about ten days after the onset of the disease. On the other hand, ataxia of case 1 remained about two months after the disease onset. Brain magnetic resonance imaging（MRI） of cases 1 and 2, showed small infarcts at the border between the right precentral gyrus and postcentral gyrus. In addition, brain MRI of case 1 disclosed another infarcts in the just medial portion of the precentral knob and the centrum semiovale of central region, respectively. It was suggested that the mechanism of cerebellar ataxia caused by infarct in the central region, was not only due to the interruption of two distinctive neuronal pathways, including the corticopontine tract and cerebellothalamocortical tract, but also due to the disturbance of sensory-motor integrity. In conclusion, etiologies of unilateral monoataxia may be heterogeneous. Furthermore, functional outcome may depend on the mechanism of unilateral monoataxia.

（Received : April 5, 2005）