PubMed2000
The clinical correlate of chronic hypercortisolism is Cushing's syndrome (CS). After exclusion of an iatrogenic cause (glucocorticoid administration), two reliable laboratory methods for establishing the diagnosis are (i) measurement of "free" (unmetabolised) cortisol in a 24-hour urine (UFC) sample and (ii) the low-dose (1 or 1.5 mg) dexamethasone (Dex) test. For the latter, Dex is taken orally at midnight, and plasma cortisol is measured at 8 a.m. In normals and in the absence of CS, the morning cortisol (200-650 nmol/L) is suppressed to <80 nmol/L. In endogenous CS of all causes, cortisol suppression by Dex is absent or incomplete. In patients with severe mental depression or stress, suppression may also be incomplete ("false-positives"). However, UFC is normal or only slight increased in the latter group, while it is always markedly increased in clinically apparent CS. In CS, UFC rises proportionally more than plasma cortisol because the cortisol binding plasma protein (transcortin) can bind only about 500 nmol/L cortisol. Protein-bound cortisol is not excreted by the kidney. After establishing the diagnosis CS, the differentiation between its pituitary (ca. 70%), adrenocortical (ca. 20%) or "ectopic" (ACTH production by non-pituitary tumours) (ca. 10%) origin is made by plasma ACTH measurement, a corticotropin releasing hormone injection test (with plasma ACTH/cortisol measurement) and a high-dose Dex (8 mg or more) suppression test. Chronic hypocorticolism can be primary (adrenal disease, Addison's disease) or secondary (pituitary or hypothalamic disorder). UFC measurement is not an established method for confirming hypocortisolism because most analytical methods are too unspecific and insensitive in the subnormal range. Low-normal or subnormal plasma cortisol plus elevated ACTH is the hallmark of Addison's disease. Injection of high doses of ACTH does not lead to a rise in plasma cortisol in these patients. A clearly subnormal cortisol plus low ACTH proves secondary hypocortisolism. Mild forms with low-normal plasma cortisol, however, are more difficult to prove. So-called "dynamic" tests stimulating the whole hypothalamo-pituitary-adrenal axis (insulin hypoglycemia test or metyrapone test) are necessary to confirm the diagnosis. Patients with hypocortisolism, depending on disease severity, must be treated permanently or only in stressful situations with hydrocortisone unless they may die after passing the clinical state of an "adrenal crisis".