A cluster of clinical abnormalities characterize Cushing's syndrome. These abnormalities result from excessive levels of adrenocortical hormones (particularly cortisol) or related corticosteroids and, to a lesser extent, androgens and aldosterone. Its unmistakable signs include adiposity of the face (moon face), neck, and trunk and purple striae on the skin.
Cushing's syndrome is most common in women. The prognosis depends on the underlying cause; it is poor in untreated persons and in those with untreatable ectopic corticotropin-producing carcinoma.
In approximately 80% of patients, Cushing's syndrome results from excess production of corticotropin and consequent hyperplasia of the adrenal cortex. Overproduction of corticotropin may stem from pituitary hypersecretion (Cushing's disease) or corticotropinproducing tumor in another organ (particularly bronchogenic or pancreatic carcinoma). Excessive administration of exogenous glucocorticoids can also cause Cushing's syndrome.
In the remaining 20% of patients, Cushing's syndrome results from a cortisol-secreting adrenal tumor that's usually benign. In infants, the usual cause of Cushing's syndrome is adrenal adenoma or carcinoma.
Signs and symptoms
Common signs and symptoms of Cushing's syndrome include:
Initially, the diagnosis of Cushing's syndrome requires determination of plasma steroid levels. In persons with normal hormone balance, plasma cortisollevels are higher in the morning and decrease gradually through the day (diurnal variation). In patients with Cushing's syndrome, cortisol levels don't fluctuate and typically remain consistently elevated; a 24-hour urine sample demonstrates elevated free cortisol levels.
Suppression test :- A low-dose dexamethasone suppression test confirms the diagnosis of Cushing's syndrome. A high-dose dexamethasone suppression test can determine whether Cushing's syndrome results from pituitary dysfunction (Cushing's disease) or from adenoma of the adrenal gland or ectopic corticotropin secretion.
In this test, dexamethasone suppresses plasma cortisol levels, and urinary 17 -hydroxycorticosteroids (17OHCS) and 17-ketogenic steroids fall to 50% or less of basal levels. Failure to suppress these levels indicates that the syndrome results from an adrenal tumor or a nonendocrine, corticotropinsecreting tumor. This test can produce false-positive results.
Stimulation test :- In a stimulation test, administration of metyrapone, which blocks cortisol production by the adrenal glands, tests the ability of the pituitary gland and the hypothalamus to detect and correct low levels of plasma cortisol by increasing corticotropin production. The patient with Cushing's syndrome reacts to this stimulus by secreting an excess of plasma corticotropin as measured by levels of urinary 17-OHCS.
If the patient has an adrenal or a nonendocrine corticotropin-secreting tumor, the pituitary gland - which is suppressed by the high cortisol levels - can't respond normally, so steroid levels remain stable or fall. The corticotropin-releasing hormone tests can also be used to help differentiate pituitary Cushing's and ectopic corticotropin syndrome.
Other tests :- Ultrasonography, a computed tomography (CT) scan, magnetic resonance imaging (MRI), or angiography localizes adrenal tumors; a CT scan and MRI of the head identify pituitary tumors.
Radiation, drug therapy, and surgery are among the treatments used to restore hormone balance and reverse Cushing's syndrome. For example, pituitarydependent Cushing's syndrome with adrenal hyperplasia and severe cushingoid symptoms - such as psychosis, poorly controlled diabetes mellitus, osteoporosis, and severe pathologic fractures - may require adenectomy or pituitary irradiation. If the patient fails to respond, bilateral adrenalectomy may be performed.
Nonendocrine corticotropin-producing tumors require excision of the tumor. Drug therapy follows (for example, with mitotane, metyrapone, or aminoglutethimide) to decrease cortisol levels if symptoms persist.
Aminoglutethimide and ketoconazole decrease cortisol levels and have been beneficial for many cushingoid patients. Aminoglutethimide alone or in combination with metyrapone may also be useful in metastatic adrenal carcinoma.
Before surgery, the patient with cushingoid symptoms should have special management to control hypertension, edema, diabetes, and cardiovascular manifestations and to prevent infection. Glucocorticoid administration on the morning of surgery can help prevent acute adrenal insufficiency during surgery.
Cortisol therapy is essential during and after surgery to help the patient tolerate the physiologic stress imposed by removal of the pituitary or adrenals. If normal cortisol production resumes, steroid therapy may be gradually tapered and eventually discontinued. However, bilateral adrenalectomy or total hypophysectomy mandates lifelong steroid replacement therapy to correct hormonal deficiencies.
Cushing's syndrome may be prevented by an awareness of the associated symptoms so that early detection can be made.
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