When a patient presents signs of Cushing's syndrome due to an ACTH-secreting pituitary adenoma, what is the first-line therapy?

Transsphenoidal resection of the tumor is the first-line therapy for patients presenting with signs of Cushing's syndrome caused by an ACTH-secreting pituitary adenoma. This surgical procedure is performed to directly remove the adenoma, which is the source of excess adrenocorticotropic hormone (ACTH) production. By excising the tumor, the production of ACTH is significantly reduced, leading to a decrease in cortisol secretion from the adrenal glands.

The rationale for this approach is based on the pathophysiology of Cushing's syndrome, where the pituitary adenoma drives hypercortisolism. Surgical resection effectively addresses the underlying cause rather than just managing symptoms or hormonal levels. Successful surgery can lead to remission of the syndrome in many cases, making it the preferred initial treatment strategy.

In contrast to surgery, options like pituitary radiation and medical adrenalectomy often come into play in cases where surgery is not feasible or if there is incomplete response, but these are not the first-line treatments. Amiloride, which primarily acts as a potassium-sparing diuretic, does not address the underlying disorder of Cushing's syndrome and is not indicated in this scenario.