Marked hypokalemia at presentation in an adolescent with ectopic ACTH syndrome secondary to a bronchial carcinoid tumor: a case report.

INTRODUCTION

Ectopic ACTH syndrome (EAS) is a rare cause of Cushing's syndrome in children and adolescents, accounting for less than 1% of pediatric cases. Compared with Cushing's disease, EAS follows a more rapid clinical course with more pronounced metabolic disturbances, among which hypokalemia is one of the most distinctive features.

CASE PRESENTATION: A 14.7-year-old male presented with a three-month history of rapid weight gain, violaceous striae, hypertension, and proximal muscle weakness. Marked hypokalemia (2.8 mmol/L) prompted endocrine work-up, which revealed ACTH-dependent hypercortisolism with loss of diurnal cortisol rhythm, elevated midnight salivary cortisol, and non-suppression on low- and high-dose dexamethasone suppression tests. Pituitary MRI was unremarkable, and the marked hypokalemia raised suspicion of an ectopic source. Thoracic CT identified a nodular lesion in the right middle lobe, with corresponding uptake on ⁶⁸Ga-DOTATATE PET/CT. Right middle lobectomy was performed, and histopathology confirmed a typical bronchial carcinoid tumor. Postoperatively, hypercortisolism resolved, electrolyte balance normalized, and Cushingoid features regressed.

CONCLUSION

Marked hypokalemia at presentation may serve as an early biochemical clue to ectopic ACTH secretion in pediatric ACTH-dependent hypercortisolism, and should prompt timely evaluation for extrapituitary sources, including bronchial carcinoid tumors.