同側の大腿骨遠位部と脛骨近位部に発症した多中心性骨巨細胞腫の1例

Multicentric Giant Cell Tumor of the Femur and Tibia at the Right Knee Joint

　多中心性骨巨細胞腫(multicentric giant cell tumor；MCGCT)は非常に稀な良性骨腫瘍である．今回われわれは同症例を経験したので，若干の文献的考察を踏まえ報告する．対象は26歳の男性で主訴は右膝関節の腫脹・疼痛であった．前医で脛骨近位骨巨細胞腫(GCT)の診断で，骨掻爬・人工骨移植が行われた．1カ月後再び右膝関節の疼痛を，大腿骨遠位に同様の骨溶解性腫瘍を認めた．同部位に針生検をし，病理診断から大腿骨遠位に発生したGCTと診断され，骨掻爬術を施行した．本症例は脛骨腫瘍の発症時に大腿骨遠位部にも溶骨性病変を認めたことから，同時発生のMCGCTと考えた．術前の血清TRACP-5b値は骨腫瘍掻爬術後速やかに著減し，その後再発が生じなかった約18カ月間，上昇しなかった．このことから，血清TRACP-5b値はGCT症例の診断・治療に際し，簡便な指標になりうると考えた．良性骨腫瘍における腫瘍掻爬術後の骨移植は，術後の早期再発発見の妨げになる可能性もあり，必ずしも必要ないと考えたが，今後さらなる検討が必要である．

　Multicentric giant cell tumor (MCGCT) is a very rare benign bone tumor.　We report a case of MCGCT occurring in the distal femur and proximal tibia of the right lower limb.

　A 26-year-old man presented at Gunma University Hospital with pain and swelling around the right knee joint.　One month before he had been treated by curettage and a hydroxyapatite bone graft for a giant cell tumor (GCT) of bone of the proximal tibia at another hospital.　Plain radiography at our hospital revealed a osteolytic lesion of the distal femur.　Examination of a computed-tomography-guided needle-biopsy specimen led to a histological diagnosis of GCT.　Because the osteolytic lesions in both the distal femur and proximal tibia occurred almost simultaneously, the final diagnosis was synchronous MCGCT.　We subsequently performed curettage on both lesions without performing bone grafts.　The preoperative serum TRACP-5b level was extremely high, but it dropped immediately after the curettage procedures, and has remained within the normal range for 18 months with no evidence of tumor recurrence.　We therefore consider TRACP-5b to be a candidate serum marker for the diagnosis and detection of GCT recurrence.　Moreover, because grafted bone may interfere with the detection of early tumor recurrence, we do not think that bone grafting should be performed after curettage for the surgical treatment of benign bone tumors.　Further study will be necessary to assess the merits of curettage with and without bone grafting for the treatment of benign bone tumors.