MRI所見のない亜急性脊髄炎にて発症し体性感覚誘発電位（SEP）が診断に有用であった原発性Sjögren症候群の1例

A Case of Subacute Myelitis Associated with Primary Sjögren Syndrome Showing No MRI Abnormality and Diagnosed by Somatosensory Evoked Potentials

　要旨　本症例は55歳女性。約半年の経過で両下肢しびれ感，両下肢の筋力低下，四肢感覚障害，直腸膀胱障害が徐々に進行し，入院時には体幹と下肢の筋力低下，第6胸髄レベル以下の全感覚障害を認めた。髄液蛋白の軽度上昇があり，繰り返し施行した脊髄MRIでは異常所見はみられなかったが，体性感覚誘発電位検査（SEP）では胸髄病変を示す所見が得られた。唾液腺造影所見，小唾液腺生検所見，抗SS-A/Ro抗体および抗SS-B/La抗体陽性から，原発性Sjögren症候群に伴う脊髄炎と診断された。ステロイド治療により下肢筋力，知覚障害，直腸膀胱障害は著明に改善し，電気生理学的にもSEP所見の正常化がみられた。臨床的にミエロパチーがありながらMRIでは異常所見を認めず，SEPが診断とステロイド治療効果判定に有用であった症例で，Sjögren症候群に伴う中枢神経障害の発症機序・症状・治療を考察する上で貴重な症例と考えられた。

　We describe a case of Sjögren syndrome presenting with subacute transverse myelopathy that improved in response to steroid therapy. A 55-year-old woman with a history of NIDDM developed progressive sensory disturbance and weakness of the both legs, and micturition disturbance during a 6-month period, resulting in walking difficulty. On admission, neurological examination revealed paraplegia with extensor plantar reflex and sensory disturbance below Th 6 level. Lumbar puncture disclosed a normal cell count and a mild elevation of protein in the CSF. As subacute myelitis at the level of Th 6 was suspected, spinal plain and enhanced MRI was performed, which revealed no abnormalities. In contrast, tibial somatosensory evoked potential（SEP） could not be evoked while median SEP was almost normal, indicating thoracic cord involvement. She was diagnosed with primary Sjögren syndrome based on xerostomia, apple-tree appearance in parotid sialography, mononuclear cell infiltration in the salivary gland biopsied, and elevated anti-SS-A and SS-B antibody titers. We considered that her myelopathy was associated with Sjögren syndrome, and started steroid pulse therapy. After three courses of steroid pulse therapy followed by oral prednisolone, she showed clinical and SEP improvements. It is conceivable that the present case may represent Sjögren syndrome complicated with myelopathy that shows no MRI abnormality and well responds to steroid therapy. SEP can be a valuable tool for assessing the presence and severity of spinal cord involvement, and the efficacy of treatments.

（Received : August 16, 2004）