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Nelson syndrome occurs when there is an absence of cortisol feedback inhibition following the removal of both adrenal glands (bilateral adrenalectomy) in patients with Cushing’s disease. This loss of negative feedback leads to an increase in the secretion of adrenocorticotropic hormone (ACTH) from the remaining pituitary tissue, resulting in the development of a pituitary adenoma.

After adrenalectomy, the body no longer has sufficient levels of cortisol, which normally suppresses ACTH production. Consequently, the pituitary gland compensates by secreting more ACTH, which can lead to the enlargement of the pituitary adenoma. Patients may present with various symptoms including hyperpigmentation due to increased ACTH, and other features related to pituitary adenoma such as headaches or visual disturbances.

Other options listed do not fit the clinical context of enlarged ACTH-secreting pituitary adenoma following bilateral adrenalectomy. Ectopic Cushing syndrome involves ACTH production by non-pituitary tumors, while the Jod-Basedow phenomenon is related to hyperthyroidism from iodine load. The Whipple triad describes the classic symptoms of hypoglycemia and does not connect to pituitary adenoma or corticosteroid regulation. Understanding this context is essential in