Rapidly progressive ACTH-dependent Cushing's disease masquerading as ectopic ACTH-producing Cushing's syndrome: illustrative case.

backgroundCushing's disease (CD) remains a challenging condition to diagnose and treat. This case study highlights the challenges of diagnosing CD when faced with discrepant clinical, biochemical, and radiological findings. OBSERVATIONS: A 62-year-old man presented with rapid evolution of symptoms, including depression, fatigue, and extreme muscle atrophy, which resulted in the patient being a wheelchair user over the course of a few months. His rapid clinical course in conjunction with hypercortisolemia in the setting of a pituitary macroadenoma involving the cavernous sinus, two large pulmonary nodules, and urine-free cortisol levels in the thousands suggested an aggressive ectopic adrenocorticotropic hormone (ACTH) source. After extensive testing ruled out CD from an ectopic source and because of the patient's abrupt clinical deterioration, the authors concluded that the source was likely an aggressive pituitary adenoma. Therefore, the authors performed an endonasal transsphenoidal approach for resection of the pituitary adenoma involving the cavernous sinus, and the patient was scheduled for radiosurgery to control tumor progression. LESSONS: Although extremely high levels of cortisol and ACTH are associated with ectopic Cushing's syndrome, they may also indicate an aggressive form of CD. Suspicion should be maintained for hypercortisolemia from a pituitary source even when faced with discrepant information that may suggest an ectopic source.