Deksametazon Süpresyon Testlerinin Hiperkortizolizm Ayırıcı Tanısında Kullanımı

Abstract

Dexamethasone suppression tests (DST) are practical, cheap and safe tests which are used to evaluate endogenous hypercortisolism. They are based on the principle that glucocorticoids exogenously given at supraphysiological doses suppress the production of CRH, ACTH and cortisol by binding to central glucocorticoid receptors. Lack of suppression of cortisol production suggest endogenous hypercortisolism. Additionally, DST may be used in the diagnosis of glucocorticoid remediable hyperaldosteronism. Due to strong glucocorticoid activity, lack of mineralocorticoid activity and lack of cross-reaction with the measurement of cortisol, dexamethasone is the preferred drug for the tests. As a screening tool in endogenous hypercortisolism, overnight 1 mg DST is used. If screening test is negative, hypercortisolism is excluded; but if the test is positive, 2-day 2 mg DST should be performed to confirm the diagnosis of Cushing’s syndrome. If endogenous hypercortisolism is confirmed, plasma ACTH should be measured. Undetectable plasma ACTH level suggest ACTH-independent Cushing’s syndrome, but inappropriately normal or high plasma ACTH level suggest ACTH-dependent Cushing’s syndrome. High dose DST (overnight 8 mg or 2-day 8 mg) should be performed to discriminate pituitary or extra-pituitary cause in the patients with ACTH-dependent Cushing’s syndrome. In the presence of pituitary Cushing’s disease, because of relatively preserved negative feedback mechanism, high dose dexamethasone may suppress ACTH. In ectopic ACTH secretion, due to lack of a normal negative feedback mechanism, ACTH cannot be suppressed by high dose dexamethasone. Extraordinarily, ectopic ACTH production in some neuroendocrine tumors may be suppressed by high dose dexamethasone, but no suppression may be observed in some patients with pituitary Cushing’s disease. When applying DST, serum and plasma samples should be collected in appropriate route, and they should be transferred by true collection tubes and in right storage conditions.