ECTOPIC ACTH-PRODUCING THYMIC NEUROENDOCRINE TUMOR MASQUERADING AS PITUITARY CUSHING’S DISEASE

Abstract

CASE
Ectopic adrenocorticotrophic hormone (ACTH) syndrome is a challenging diagnosis. It is responsible for 10-20% of Cushing’s syndrome. We describe a 23-year-old Malaysian male who presented with Cushingoid features and severe hypokalaemia. Based on biochemical and radiological findings, he was initially diagnosed with pituitary Cushing’s disease and underwent pituitary adenomectomy. However, plasma ACTH level and serum cortisol were persistently raised postoperatively. The histopathological examination of the pituitary lesion revealed pituitary hyperplasia with negative ACTH staining. Further evaluation disclosed a sizeable mediastinal mass proven to be a carcinoid tumor. He achieved hypocortisolism after excision of the mediastinal mass with improved clinical parameters. This case prompts us to have a high index of suspicion for ectopic ACTH syndrome in cases of florid Cushing’s with stark biochemical parameters such as severe hypokalaemia and metabolic alkalosis.