MRI での皮質下 FLAIR 低信号から早期に疑い得た抗ミエリンオリゴデンドロサイト糖蛋白質抗体関連皮質性脳炎の 1 例

A 32-year-old male presented with unilateral orbital-temporal pulsatile headache, followed by fever in the 38°C range and nausea. The patient experienced two episodes of transient dysarthria and tinnitus, each lasting several minutes. MRI revealed swelling of the left cerebral cortex, enhancement of the leptomeninges, dilation of the left middle cerebral artery, and subcortical FLAIR hypointensity. The clinical presentation and MRI findings raised suspicions of myelin oligodendrocyte glycoprotein (MOG) antibody-associated cortical encephalitis. After two courses of steroid pulse therapy, the patient’s headache subsided, and there was a significant improvement in the swelling of the left cerebral cortex. Subsequently, serum MOG antibody positivity was confirmed. While unilateral cortical FLAIR hyperintensity and increased blood flow can be observed in various diseases, MOG antibody-associated cortical encephalitis is notably characterized by subcortical FLAIR hypointensity, a finding more frequently observed in this condition compared to other diseases. In this case, the findings were useful for early diagnosis and intervention.