Cushing's syndrome results from sus

Cushing's syndrome results from sustained hypercortisolemia. The most common cause is administration of exogenous glucocorticoids. Secretion of corticotropin from the pituitary (Cushing's disease) accounts for approximately 70% of endogenous cases; adrenal tumors and the ectopic production of corticotropin each account for approximately 15% of cases. 3 The clinical and laboratory features of Cushing's syndrome overlap with many other medical conditions, and very few patients fulfill the classic presentation of facial rounding, weight gain, striae, hirsutism, hypertension, and muscle weakness. The majority of patients have abnormal glucose tolerance, but edema and hypokalemic alkalosis, as seen in this patient, occur in only a minority. This patient had gynecomastia, which is not typical in Cushing's syndrome but can be a manifestation of hypogonadism or a consequence of hyperestrogenemia from a hormonally active tumor. Gynecomastia occurs in approximately 10% of men treated with bicalutamide.
The diagnosis of Cushing's syndrome requires the confirmation of hypercortisolism, generally with the measurement of 24-hour urinary cortisol excretion, measurement of midnight salivary cortisol levels, or both. Autonomous production of cortisol can be demonstrated with the use of a dexamethasone (1-mg) suppression test. Once hypercortisolism is established, a corticotropin level of more than 20 pg per milliliter (4.4 pmol per liter) suggests corticotropin dependency; a level below 5 pg per milliliter (1 pmol per liter) suggests an adrenal source. When corticotropin dependency is established, magnetic resonance imaging can identify pituitary tumors approximately 60% of the time.4
The patient's left-sided facial droop and left-sided epistaxis are not readily attributable to a benign pituitary adenoma. Nevertheless, pituitary enlargement in response to a tumor that produces corticotropin-releasing hormone or a primary benign or malignant pituitary tumor could account for some of the patient's visual symptoms.
The standard method for differentiating between Cushing's disease and the ectopic production of corticotropin involves venous sampling from the inferior petrosal sinus. Cushing's disease is the most likely diagnosis if the sinus-to-peripheral-vein ratio of plasma corticotropin is at least 2:1 before or at least 3:1 after injection of corticotropin-releasing hormone during sampling from the inferior petrosal sinus. Ectopic production of corticotropin is implicated if 8 mg of dexamethasone does not suppress the plasma cortisol level, although this test lacks sensitivity.