Which test can confirm a diagnosis of Cushing's disease after initial suspicion?

The high-dose dexamethasone suppression test is considered the confirmatory test for Cushing's disease after initial suspicion has arisen. This test is based on the principle that in normal individuals and those with conditions other than Cushing's disease, administration of dexamethasone, a synthetic glucocorticoid, will suppress cortisol production due to negative feedback on the hypothalamus and pituitary gland.

In the case of Cushing's disease, which is primarily caused by a pituitary adenoma secreting adrenocorticotropic hormone (ACTH), cortisol production will not be suppressed even by high doses of dexamethasone. This resistance to suppression is a key factor in differentiating Cushing's disease from other causes of Cushing's syndrome, such as adrenal tumors or ectopic ACTH syndrome, where suppression may still occur.

The other tests, while useful in the overall diagnosis and management of Cushing's syndrome, do not definitively confirm Cushing's disease. An electrolyte panel can provide insights into electrolyte imbalances often seen in patients with Cushing's but does not specifically confirm the disease. Serum cortisol measurement is crucial in the initial assessment of cortisol levels but does not discriminate between different causes of hypercort