J Korean Endocr Soc.  2007 Oct;22(5):359-364. 10.3803/jkes.2007.22.5.359.

A Case of Ectopic ACTH Syndrome Associated with Small Cell Lung Cancer Presented with Hypokalemia

Affiliations
  • 1Department of Internal Medicine, College of Medicine, The Catholic University of Korea.

Abstract

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 11beta-hydroxysteroid dehydrogenase type 2 (11beta-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.

Keyword

Ectopic ACTH syndrome; hypokalemia; small cell lung cancer

MeSH Terms

11-beta-Hydroxysteroid Dehydrogenase Type 2
ACTH Syndrome, Ectopic*
Adrenocorticotropic Hormone
Aged
Alkalosis
Biopsy
Cortisone
Cushing Syndrome
Dexamethasone
Diagnosis, Differential
Female
Humans
Hydrocortisone
Hypertension
Hypokalemia*
Lung
Patient Rights
Plasma
Receptors, Mineralocorticoid
Renin
Small Cell Lung Carcinoma*
11-beta-Hydroxysteroid Dehydrogenase Type 2
Adrenocorticotropic Hormone
Cortisone
Dexamethasone
Hydrocortisone
Receptors, Mineralocorticoid
Renin

Figure

  • Fig. 1 Adrenal CT scan shows bilateral hyperplasia of adrenal glands.

  • Fig. 2 Pituitary MRI shows no definite abnormalities.

  • Fig. 3 Chest PA shows no definite abnormalities, but chest CT scan shows 3 cm sized mass (arrow) in the right lower lobe.

  • Fig. 4 Bronchoscopy shows endobronchial mass in the basal segment of right lower lobe.

  • Fig. 5 Histological features of bronchial mass. Hematoxylin-Eosin stained section shows poorly differentiated small cell carcinoma (A: ×400). The tumor cells are negative for NSE (B: ×400) and positive for synaptophysin (C: ×400), chromogranin (D: ×400) and CD56 (E: ×400) by immunohistochemical staining. The tumor cells are negative for ACTH (F: ×400).


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