抄録
32歳男性.主訴は左陰嚢腫大.血清hCGβ,LDHの上昇を認めた.CTで傍大動脈領域に小さなリンパ節腫大を認めた.左高位精巣摘除術施行し,病理組織診断はセミノーマであった.臨床病期IIAと診断し,術後にシスプラチン,エトポシド,ブレオマイシンを用いた化学療法を2コース施行した.化学療法前に認めたリンパ節と思われた小病変は不変で,血管もしくは結合組織と考えられた.臨床的には完全緩解と考えられ,LDHは正常化したが,血清hCGβは低値陽性のまま持続していた.血清hCGは化学療法前後共に正常,化学療法後の尿中hCGβは測定感度以下であった.希釈液に異好性阻害物質としてマウス血清を用いて,本症例とコントロールの血清を2倍,4倍に希釈して血清hCGβを測定した.コントロールの血清は希釈倍率に比例して測定値が低下したのに対して,本症例の血清では急速な低下を示した.化学療法後8カ月経過するが血清hCGβは低値陽性のまま上昇は認めず,再発なく経過している.これらの結果から本症例の血清hCGβ上昇は偽陽性と考えられ,その鑑別に尿中hCGβの測定と異好性阻害物質による希釈測定が有用であった.
A 32-year-old male consulted a hospital with a complaint of left scrotal swelling. Serum hCGβ and LDH levels were elevated and computed tomography demonstrated a suspicious small lymphadenopathy in the paraaortic region. Left inguinal orchiectomy was performed. Histological examination demonstrated seminoma. We diagnosed the disease as clinical stage 2A and the patient received 2 courses of chemotherapy with cisplatin, etoposide and bleomycin. After this therapy, the small lymphadenopathy in the paraaortic region did not decrease in size. We considered this lesion a vessel or connective tissue. Although he achieved clinical complete remission and serum LDH level was normalized, the serum hCGβ level remained low level positive. Urinary hCGβ level after chemotherapy was below the threshold of detectability. We measured the serum from this patient as well as control sera by two- and four-fold dilution with a diluent comprised of mouse serum as a heterophilic antibody-blocking agent. The serum hCGβ level of this patient was obviously decreased; in contrast, control sera were decreased in parallel. The serum hCGβ level of this patient remained low level positive without recurrence for 8 months after chemotherapy. These results strongly suggested that low level of positivity for serum hCGβ in this case was a false positive finding. We consider the measurement of urinary hCGβ and dilution measurement using a heterophilic antibody-blocking agent to be useful methods of distinguishing false positive findings for serum hCGβ.
