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이소성 ACTH 증후군은 원인 종양이 빠르게 진행하는 경우가 많아서 다른 쿠싱증후군과는 다르게 복부비만, 선상 선조 등의 특징적인 증상은 드물고, 원발성 알데스토론증과 같이 저칼륨혈증을 동반한 대사성 알칼리증과 고혈압 증상이 흔하다. 그러므로 고혈압과 저칼륨혈증 증상을 보이지만 다른 원인이 발견되지 않는 경우에는 원인 질환으로서 쿠싱증후군을 고려해야 하며, 특히 이소성 ACTH 증후군에 대한 확인이 필요하다. 저자들은 고혈압과 저칼륨혈증 및 대사성 알칼리증을 보였던 환자에서 원인 질환으로 소세포폐암에 의한 이소성 ACTH 증후군을 진단한 1예를 경험하였기에 보고하는 바이다.


We report a case of a 73-year-old female patient who was diagnosed with ectopic ACTH syndrome caused by small cell lung cancer. We initially presumed that the patient was in a state of mineralocorticoid excess, because she had hypertension and hypokalemic alkalosis. This was however excluded because her plasma renin activity was not suppressed and her plasma aldosterone/plasma renin activity ratio was below 25. Moreover, her 24 hour urine free cortisol level was elevated and her serum cortisol levels after a low dose dexamethasone suppression test, were not suppressed. Furthermore, her basal plasma ACTH and serum cortisol levels increased and her serum cortisol level after a high dose dexamethasone suppression test was not suppressed. We performed studies to identify the source of ectopic ACTH syndrome and found a 3 cm-sized mass in the patient’s right lower lobe of her lung, which was eventually diagnosed as small cell lung cancer following a bronchoscopic biopsy. In conclusion, Cushing’s syndrome, and in particular ectopic ACTH syndrome, must be considered in the differential diagnosis of mineralocorticoid-induced hypertension. The excessive cortisol saturates the 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) activity, which in turn, inactivates the conversion of cortisol to cortisone in the renal tubules. Moreover, excessive cortisol causes binding to the mineralocorticoid receptors, causing mineralocorticoid hypertension, characterized by severe hypercortisolism. (J Kor Endocrine Soc 22:359~364, 2007)