An Unusual Cause of Hypertension and Hypokalemia: ACTH-Producing Pulmonary Carcinoid

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Pulmonary carcinoids are slow-growing tumors contributing to 2% of primary lung tumors. Endocrine manifestations like adrenocorticotropic hormone (ACTH) production from carcinoids account for 1% of all cases of cushing syndrome.¹

A 32-year-old male presented with poorly controlled hypertension, recurrent hypokalemia and fatigue. He experienced trouble climbing stairs, noticed easy bruising, truncal obesity, decreased libido, hair thinning, and new abdominal wall stretch marks. He had round facies, facial plethora, dorsal cervical fat prominence, and wide violaceous striae on the abdomen and axillary areas.

Work up showed normal kidney function, and serum potassium of 3.1 mEq/L. His morning serum cortisol was 55.0 µg/dL (normal range 4.0-22.0 µg/dL) without suppression by overnight low-dose dexamethasone, high urine free cortisol at 1938.9 µg/24 hours (normal 4.0-50.0 µg/24 hours) and elevated ACTH level at 196 pcg/mL (normal 6-50 pcg/mL) pointing towards either pituitary Cushing disease or ectopic ACTH production. Failure to suppress ACTH with high-dose dexamethasone favored the latter. MRI scan showed a normal pituitary. Hence, it was decided not to pursue inferior petrosal sinus sampling (IPSS).² Abdominal CT scan was unremarkable. Contrast-enhanced chest CT scan showed a solid, noncalcified, 1.9 cm peribronchiolar left lower lobe nodule with faint enhancement, which lead to suspicion of carcinoid.

After pre-treatment with 11β-hydroxylase inhibitor osilodrostat that lowers cortisol³ and perioperative use of stress-dose steroid, the patient underwent video-assisted left lower lobectomy. Pathology revealed a carcinoid tumor with a negative margin and a positive ACTH stain [Figure 1]. Hypokalemia resolved, and the patient became normotensive over the next several days. Serum AM free cortisol level normalized 1 month later, and urine free cortisol level returned to normal 1 year later. The patient is currently doing well.

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Figure 1:

(a) Hematoxylin and eosin stain showing nests of neoplastic cells with polygonal to round nuclei with salt and pepper chromatin (red arrows, 200x). The neoplastic cells are diffusely positive for (b) synaptophysin (200x), (c) chromogranin B (200x) and (d) ACTH on immunohistochemistry (200x); all marked with red arrows.

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Typical features of Cushing syndrome are seen in slow-growing tumors with ACTH production.⁴ Presence of symptoms and lymph node metastasis at the time of diagnosis are adverse prognostic factors.⁵ Surgical resection is curative in up to 80% of patients with identifiable tumors.