Cushing Syndrome
Diseases

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EPIDEMIOLOGY:

Iatrogenic Cushing's (caused by treatment with corticosteroids) is the most common form of Cushing's syndrome. The incidence of pituitary tumors may be relatively high, as much as one in five people, [5] but only a minute fraction are active and produce excessive hormones.

SYMPTOMS:

Symptoms include rapid weight gain , particularly of the trunk and face with sparing of the limbs (central obesity), a round face often referred to as a "moon face", excess sweating, telangiectasia (dilation of capillaries), thinning of the skin (which causes easy bruising) and other mucous membranes, purple or red striae (the weight gain in Cushing's stretches the skin, which is thin and weakened, causing it to hemorrhage) on the trunk, buttocks, arms, legs or breasts, proximal muscle weakness (hips, shoulders), and hirsutism (facial male-pattern hair growth). A common sign is the growth of fat pads along the collar bone and on the back of the neck (known as a lipodystrophy). The excess cortisol may also affect other endocrine systems and cause, for example, insomnia, reduced libido, impotence, amenorrhoea and infertility. Patients frequently suffer various psychological disturbances, ranging from euphoria to psychosis. Depression and anxiety are also common.²

Other signs include persistent hypertension (due to cortisol's enhancement of epinephrine's vasoconstrictive effect) and insulin resistance (especially common in ectopic "ACTH": http://en.wikipedia.org/wiki/Adrenocorticotropic_hormone production), leading to hyperglycemia (high blood sugars) which can lead to diabetes mellitus. Untreated Cushing's syndrome can lead to heart disease and increased mortality. Cushing's syndrome due to excess ACTH may also result in hyperpigmentation. This is due to Melanocyte-Stimulating Hormone production as a byproduct of ACTH synthesis from Proopiomelanocortin (POMC). Cortisol can also exhibit mineralcorticoid activity in high concentrations, worsening the hypertension and leading to hypokalemia (common in ectopic ACTH secretion). Furthermore, gastrointestinal disturbances, opportunistic infections and impaired wound healing (cortisol is a stress hormone, so it depresses the immune and inflammatory responses). Osteoporosis is also problem in Cushing's Syndrome, as mentioned before, cortisol evokes a stress-like response. The body's maintenance of bone (and other tissues) is therefore no longer one of its main priorities, so to speak.

Exogenous Versus Endogenous

There are two types of Cushing’s syndrome: exogenous and endogenous. In endogenous disease, excess cortisol production within the body is the cause, whilst in exogenous disease the causal factor is typically steroid medication (i.e. it originates outside the body) mimicing cortisol's activity. The signs and symptoms are therefore virtually identical, aside from those induced by ACTH in pituitary-dependent disease and ectopic ACTH-producing tumours (such as hyperpigmentation). The exogenous route is by far the most commonly taken in Cushing’s syndrome (a fact that all too many seem to forget). Examples of such exogenous steroid medications are those used to treat inflammatory disorders such as asthma and rheumatoid arthritis, or to suppress the immune system after an organ transplant. This type of Cushing’s is temporary and goes away after the patient has finished taking the cortisol-like medications. Endogenous Cushing’s syndrome is unusual, it usually comes on slowly and can be difficult to diagnose.

DIAGNOSIS:

Diagnosis is based on a review of the patient's medical history, physical examination and laboratory tests. Often x-ray exams of the adrenal or pituitary glands are useful for locating tumors. These tests help to determine if excess levels of cortisol are present and why.

-_24-Hour Urinary Free Cortisol Level_

This is the most specific diagnostic test. The patient's urine is collected over a 24-hour period and tested for the amount of cortisol. Levels higher than 50–100 micrograms a day for an adult suggest Cushing's syndrome. The normal upper limit varies in different laboratories, depending on which measurement technique is used.

Once Cushing's syndrome has been diagnosed, other tests are used to find the exact location of the abnormality that leads to excess cortisol production. The choice of test depends, in part, on the preference of the endocrinologist or the center where the test is performed.

-_Dexamethasone Suppression Test_

This test helps to distinguish patients with excess production of ACTH due to pituitary adenomas from those with ectopic ACTH-producing tumors. Patients are given dexamethasone, a synthetic glucocorticoid, by mouth every 6 hours for 4 days. For the first 2 days, low doses of dexamethasone are given, and for the last 2 days, higher doses are given. Twenty-four hour urine collections are made before dexamethasone is administered and on each day of the test. Since cortisol and other glucocorticoids signal the pituitary to lower secretion of ACTH, the normal response after taking dexamethasone is a drop in blood and urine cortisol levels. Different responses of cortisol to dexamethasone are obtained depending on whether the cause of Cushing's syndrome is a pituitary adenoma or an ectopic ACTH-producing tumor.

The dexamethasone suppression test can produce false-positive results in patients with depression, alcohol abuse, high estrogen levels, acute illness, and stress. Conversely, drugs such as phenytoin and phenobarbital may cause false-negative results in response to dexamethasone suppression. For this reason, patients are usually advised by their physicians to stop taking these drugs at least one week before the test.

-_CRH Stimulation Test_

This test helps to distinguish between patients with pituitary adenomas and those with ectopic ACTH syndrome or cortisol-secreting adrenal tumors. Patients are given an injection of CRH, the corticotropin-releasing hormone which causes the pituitary to secrete ACTH. Patients with pituitary adenomas usually experience a rise in blood levels of ACTH and cortisol. This response is rarely seen in patients with ectopic ACTH syndrome and practically never in patients with
cortisol-secreting adrenal tumors.

-_Direct Visualization of the Endocrine Glands (Radiologic Imaging)_

Imaging tests reveal the size and shape of the pituitary and adrenal glands and help determine if a tumor is present. The most common are the CT (computerized tomography) scan and MRI (magnetic resonance imaging). A CT scan produces a series of x-ray pictures giving a cross-sectional image of a body part. MRI also produces images of the internal organs of the body but without exposing the patient to ionizing radiation.

Imaging procedures are used to find a tumor after a diagnosis has been established. Imaging is not used to make the diagnosis of Cushing's syndrome because benign tumors, sometimes called "incidentalomas," are commonly found in the pituitary and adrenal glands. These tumors do not produce hormones detrimental to health and are not removed unless blood tests show they are a cause of symptoms or they are unusually large. Conversely, pituitary tumors are not detected by imaging in almost 50 percent of patients who ultimately require pituitary surgery for Cushing's syndrome.

-_Petrosal Sinus Sampling_

This test is not always required, but in many cases, it is the best way to separate pituitary from ectopic causes of Cushing's syndrome. Samples of blood are drawn from the petrosal sinuses, veins which drain the pituitary, by introducing catheters through a vein in the upper thigh/groin region, with local anesthesia and mild sedation. X-rays are used to confirm the correct position of the catheters. Often CRH, the hormone which causes the pituitary to secrete ACTH, is given during this test to improve diagnostic accuracy. Levels of ACTH in the petrosal sinuses are measured and compared with ACTH levels in a forearm vein. ACTH levels higher in the petrosal sinuses than in the forearm vein indicate the presence of a pituitary adenoma; similar levels suggest ectopic ACTH syndrome.

-_The Dexamethasone-CRH Test_

Some individuals have high cortisol levels, but do not develop the progressive effects of Cushing's syndrome, such as muscle weakness, fractures and thinning of the skin. These individuals may have Pseudo Cushing's syndrome, which was originally described in people who were depressed or drank excess alcohol, but is now known to be more common. Pseudo Cushing's does not have the same long-term effects on health as Cushing's syndrome and does not require treatment directed at the endocrine glands. Although observation over months to years will distinguish Pseudo Cushing's from Cushing's, the dexamethasone-CRH test was developed to distinguish between the conditions rapidly, so that Cushing's patients can receive prompt treatment. This test combines the dexamethasone suppression and the CRH stimulation tests. Elevations of cortisol during this test suggest Cushing's syndrome.

Some patients may have sustained high cortisol levels without the effects of Cushing's syndrome. These high cortisol levels may be compensating for the body's resistance to cortisol's effects. This rare syndrome of cortisol resistance is a genetic condition that causes hypertension and chronic androgen excess.

Sometimes other conditions may be associated with many of the symptoms of Cushing's syndrome. These include polycystic ovarian syndrome, which may cause menstrual disturbances, weight gain from adolescence, excess hair growth and sometimes impaired insulin action and diabetes. Commonly, weight gain, high blood pressure and abnormal levels of cholesterol and triglycerides in the blood are associated with resistance to insulin action and diabetes; this has been described as the "Metabolic Syndrome-X." Patients with these disorders do not have abnormally elevated cortisol levels.

PATHOPHISIOLOGY

Both the "hypothalamus": http://en.wikipedia.org/wiki/Hypothalamus and the pituitary gland are in the brain. The hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the pituitary gland to release corticotropin (ACTH). ACTH travels via the blood to the adrenal gland, where it stimulates the release of cortisol. Cortisol is secreted by the cortex of the adrenal gland from a region called the zona fasciculata in response to ACTH. Elevated levels of cortisol exert negative feedback on the pituitary, which decreases the amount of ACTH released from the pituitary gland. Strictly, Cushing's syndrome refers to excess cortisol of any etiology. One of the causes of Cushing's syndrome is a cortisol secreting adenoma in the cortex of the adrenal gland. The adenoma causes cortisol levels in the blood to be very high, and negative feedback on the pituitary from the high cortisol levels causes ACTH levels to be very low. Cushing's disease refers only to hypercortisolism secondary to excess production of ACTH from a corticotrophic pituitary adenoma. This causes the blood ACTH levels to be elevated along with cortisol from the adrenal gland. The ACTH levels remain high because a tumor causes the pituitary to be unresponsive to negative feedback from high cortisol levels.

h3. PATHOGENESIS

Cushing's syndrome can also be caused by three different categories of disease:

* a pituitary tumor producing abnormally large quantities of ACTH
* the abnormal production of ACTH by some source other than the pituitary
* a tumor within the adrenal gland overproducing cortisol

Although it is rare, about two-thirds of endogenous (occurring within the body rather than from a source outside the body, like a medication) Cushing's syndrome is a result of Cushing's disease. The term "Cushing's disease" refers to Cushing's syndrome, which is caused by excessive secretion of ACTH by a pituitary tumor, usually an adenoma (noncancerous tumor). The pituitary tumor causes increased growth of the adrenal cortex (hyperplasia) and increased cortisol production. Cushing's disease affects women more often than men.

Tumors in locations other than the pituitary can also produce ACTH. This is called ectopic ACTH syndrome ("ectopic" refers to something existing out of its normal place). Tumors in the lung account for more than half of all cases of ectopic ACTH syndrome. Other types of tumors which may produce ACTH include tumors of the thymus, the pancreas, the thyroid, and the adrenal gland. In each case, the secreting part of the tumor may be in the primary tumor, part of the primary tumor, or may be a small, difficult-to-find, metastatic lesion(s). Nearly all adrenal gland tumors are benign (noncancerous), although in rare instances a tumor may actually be cancerous.

Familial Cushing syndrome

Cushing syndrome can also develop in multiple individuals from the same family. This familial form is due to a genetically inherited susceptibility to developing specific endocrine tumors. The specific nature of the genetic components have not been clearly elucidated, except in cases of a rare genetic disease called Multiple Endocrine Neoplasia. MEN is caused by a genetic mutations in a specific gene involved in cell cycle regulation resulting in pituitary tumors that can lead to Cushing syndrome.

Complications

If you don't receive prompt treatment for Cushing's syndrome, other complications may occur, such as:

* Bone loss (osteoporosis), due to the damaging effects of excess cortisol
* High blood pressure (hypertension)
* Kidney stones
* Diabetes
* Unusual infections

When the cause of Cushing's syndrome is a pituitary tumor (Cushing's disease), it can sometimes lead to other problems, such as interfering with the production of other hormones that the pituitary controls.

Treatment

Treatment depends on the specific reason for cortisol excess and may include surgery, radiation, chemotherapy or the use of cortisol-inhibiting drugs. If the cause is long-term use of glucocorticoid hormones to treat another disorder, the doctor will gradually reduce the dosage to the lowest dose adequate for control of that disorder. Once control is established, the daily dose of glucocorticoid hormones may be doubled and given on alternate days to lessen side effects.

Pituitary Adenomas
Several therapies are available to treat the ACTH-secreting pituitary adenomas of Cushing's disease. The most widely used treatment is surgical removal of the tumor, known as transsphenoidal adenomectomy. Using a special microscope and very fine instruments, the surgeon approaches the pituitary gland through a nostril or an opening made below the upper lip. Because this is an extremely delicate procedure, patients are often referred to centers specializing in this type of surgery. The success, or cure, rate of this procedure is over 80 percent when performed by a surgeon with extensive experience. If surgery fails, or only produces a temporary cure, surgery can be repeated, often with good results. After curative pituitary surgery, the production of ACTH drops two levels below normal. This is a natural, but temporary, drop in ACTH production, and patients are given a synthetic form of cortisol (such as hydrocortisone or prednisone). Most patients can stop this replacement therapy in less than a year.

For patients in whom transsphenoidal surgery has failed or who are not suitable candidates for surgery, radiotherapy is another possible treatment. Radiation to the pituitary gland is given over a 6-week period, with improvement occurring in 40 to 50 percent of adults and up to 80 percent of children. It may take several months or years before patients feel better from radiation treatment alone. However, the combination of radiation and the drug mitotane (Lysodren®) can help speed recovery. Mitotane suppresses cortisol production and lowers plasma and urine hormone levels. Treatment with mitotane alone can be successful in 30 to 40 percent of patients. Other drugs used alone or in combination to control the production of excess cortisol are aminoglutethimide, metyrapone, trilostane and ketoconazole. Each has its own side effects that doctors consider when prescribing therapy for individual patients.

Ectopic ACTH Syndrome
To cure the overproduction of cortisol caused by ectopic ACTH syndrome, it is necessary to eliminate all of the cancerous tissue that is secreting ACTH. The choice of cancer treatment—surgery, radiotherapy, chemotherapy, immunotherapy, or a combination of these treatments—depends on the type of cancer and how far it has spread. Since ACTH-secreting tumors (for example, small cell lung cancer) may be very small or widespread at the time of diagnosis, cortisol-inhibiting drugs, like mitotane, are an important part of treatment. In some cases, if pituitary surgery is not successful, surgical removal of the adrenal glands (bilateral adrenalectomy) may take the place of drug therapy.

Adrenal Tumors
Surgery is the mainstay of treatment for benign as well as cancerous tumors of the adrenal glands. In Primary Pigmented Micronodular Adrenal Disease and the familial Carney's complex, surgical removal of the adrenal glands is required.