摘出病巣にCOX-2発現を証明できた腰椎椎弓類骨骨腫の1例

Osteoid Osteoma of a Lumbar Lamina with COX-2 Expression : Case Report

　抄録：類骨骨腫は，夜間痛やアスピリン著効といった特徴的臨床症状を呈し，炎症性の性格を有するが，その病態は明らかでない．今回，腰椎椎弓に発生し圧迫所見の認められない神経根に症状が発現した1例を経験し，炎症惹起物質であるprostaglandin（PG）の代謝酵素であるcyclooxygenase-2（COX-2）の発現とその意義について検討した．症例は，14歳男性．術前の臨床症状は腰痛に加え右下肢tension sign陽性で，前けい骨筋，長母趾伸筋に軽度の筋力低下を認めた．術前MRIにて第5椎弓右側にnidusを認め，nidus周囲の骨および軟部組織に強い造影効果を認めた．手術摘出標本における抗COX-2抗体を用いた免疫組織化学的検索では，nidus内の腫瘍性増殖を示す骨芽細胞の細胞質に強い染色が認められた．また，RT-PCRによる検討ではnidusにおいてCOX-2mRNAの強い発現が認められた．本症例の圧迫所見のない神経根症状は，nidus内腫瘍性骨芽細胞でのCOX-2発現によるPG産生経路の賦活化によると思われた．

　Osteoid osteoma is a benign bone tumor manifesting typical symptoms of inflammation, such as nocturnal pain and marked NSAID responsiveness, but its true pathogenesis remains unknown. Expression of cyclooxygenase-2 (COX-2), an inducible enzyme of arachidonic acid metabolism, was investigated, to clarify the mechanism of the radiculopathy without nerve root compression in osteoid osteoma of a lumbar vertebral arch.

　The patient was a 17-year-old male, with osteoid osteoma of the 5th lumbar vertebral arch associated with radiculopathy. The patient showed mild weakness of muscles predominantly innervated by the L5 nerve root, but no compression of the L5 nerve root was detected by computed tomography (CT) or magnetic resonance imaging (MRI).

　Strong expression of COX-2 by the osteoblasts in the nidus was detected by immunohistochemistry and the reverse transcription-polymerase reaction (RT-PCR). Immunohistochemistry, showed diffuse and intense immunoreactivity for COX-2 in nearly all of the short-spindled or polygonal osteoblasts within the nidus. The RT-PCR findings, showed that COX-2mRNA expression in the nidus was about ten times stronger than in the surrounding bone or control bone, according to the numerical data for DNA bands on agarose gels. Radiculopathy without nerve root compression may be followed by the spreads of the inflammatory reaction due to COX-2 expression in the nidus.