Paraneoplastik Ektopik Cushing Sendromu
Özet
Paraneoplaztik sendromlar, tümörlerin salgıladığı metabolitlerin uzak etkileriyle ortaya çıkan ve bazen primer kanser tanısının konulmasını sağlayan klinik tablolardır. Bu kapsamda değerlendirilen Paraneoplaztik Ektopik Cushing Sendromu (CS), hipofiz dışı dokulardan kontrolsüz ACTH veya CRH salgılanması sonucu adrenal bezde hiperplazi ve kortizol fazlalığı ile karakterizedir. Genellikle küçük hücreli akciğer kanseri, bronşiyal karsinoid ve timus gibi tümörlerde görülür. Klasik CS bulguları santral obezite ve pletora iken, ektopik olgularda zayıflama daha ön plandadır. Tanı sürecinde idrar, tükürük ve deksametazon baskılama gibi birinci basamak tarama testlerini takiben plazma ACTH düzeyinin ölçüldüğü ikinci basamak testler uygulanır. ACTH bağımlı hipofizer köken ile ektopik kaynakların ayrımında yüksek doz deksametazon, metirapon, CRH testleri ve inferior petröz sinüs örneklemesi (İPSS) kritik role sahiptir. Tümör dokusundaki POMC geni transkripsiyon farklılıkları, düşük biyolojik aktiviteye sahip ACTH-benzeri fragmanların üretimine yol açar. Görüntülemede MRG, BT ve ileri nükleer tıp yöntemlerinden (FDG PET, Ga-68) faydalanılır. Tedavi primer tümörün cerrahi olarak çıkarılmasına dayanmakla birlikte, kaynak saptanamadığında ilaç tedavisi veya bilateral adrenalektomi uygulanır. Hayati risk taşıyan bu sendromların erken tanı ve tedavisi klinik açıdan büyük önem taşımaktadır.
Paraneoplastic syndromes are distant manifestations caused by tumor-secreted metabolites, which can occasionally precede the diagnosis of the primary malignancy. Paraneoplastic Ectopic Cushing's Syndrome (CS) is characterized by adrenal hyperplasia and excess cortisol production resulting from the chronic, autonomous secretion of ACTH or CRH from extra-pituitary tissues. It is most frequently associated with small cell lung cancer, bronchial carcinoids, and thymic tumors. While classic CS presents with central obesity and plethora, ectopic cases often manifest predominantly with weight loss. Diagnosis involves first-line screening via urinary, salivary, and dexamethasone suppression tests, followed by plasma ACTH measurement. High-dose dexamethasone, metyrapone, CRH tests, and inferior petrosal sinus sampling (IPSS) are utilized to differentiate pituitary-driven Cushing's disease from ectopic sources. Alterations in POMC gene promoter usage within tumor cells lead to the overproduction of ACTH-like precursors with lower bioactivity. Localization of the source relies on high-resolution CT, MRI, and molecular imaging strategies like FDG PET or Gallium-68 receptor scintigraphy. Treatment focuses on complete surgical resection of the tumor, whereas medical therapy or bilateral adrenalectomy is indicated for occult or unresectable disease. Early detection remains critical due to the life-threatening nature of severe paraneoplastic complications.
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