Cushing's syndrome is a collection of signs and symptoms due to prolonged exposure to glucocorticoids such as cortisol. Signs and symptoms may include high blood pressure, abdominal obesity but with thin arms and legs, reddish stretch marks, a round red face due to facial plethora, a fat lump between the shoulders, weak muscles, weak bones, acne, and fragile skin that heals poorly. Women may have more hair and irregular menstruation or loss of menses, the exact mechanism of which are unknown. Occasionally there may be changes in mood, headaches, and a chronic feeling of tiredness.
Cushing's syndrome is caused by either excessive cortisol-like medication, such as prednisone, or a tumor that either produces or results in the production of excessive cortisol by the adrenal glands. Cases due to a pituitary adenoma are known as Cushing's disease, which is the second most common cause of Cushing's syndrome after medication. A number of other tumors, often referred to as ectopic due to their placement outside the pituitary, may also cause Cushing's. Some of these are associated with inherited disorders such as multiple endocrine neoplasia type 1 and Carney complex. Diagnosis requires a number of steps. The first step is to check the medications a person takes. The second step is to measure levels of cortisol in the urine, saliva or in the blood after taking dexamethasone. If this test is abnormal, the cortisol may be measured late at night. If the cortisol remains high, a blood test for ACTH may be done.
Most cases can be treated and cured. If brought on by medications, these can often be slowly decreased if still required or slowly stopped. If caused by a tumor, it may be treated by a combination of surgery, chemotherapy, and/or radiation. If the pituitary was affected, other medications may be required to replace its lost function. With treatment, life expectancy is usually normal. Some, in whom surgery is unable to remove the entire tumor, have an increased risk of death.
About two to three cases per million persons are caused overtly by a tumor. It most commonly affects people who are 20 to 50 years of age. Women are affected three times more often than men. A mild degree of overproduction of cortisol without obvious symptoms, however, is more common. Cushing's syndrome was first described by American neurosurgeon Harvey Cushing in 1932. Cushing's syndrome may also occur in other animals including cats, dogs, and horses.
Signs and symptoms
Symptoms include rapid weight gain, particularly of the trunk and face with sparing of the limbs (central obesity). Common signs include the growth of fat pads along the collarbone, on the back of the neck ("buffalo hump" or lipodystrophy), and on the face ("moon face"). Other symptoms include excess sweating, dilation of capillaries, thinning of the skin (which causes easy bruising and dryness, particularly the hands) and mucous membranes, purple or red striae (the weight gain in Cushing's syndrome 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), baldness and/or extremely dry and brittle hair. In rare cases, Cushing's can cause hypocalcemia. The excess cortisol may also affect other endocrine systems and cause, for example, insomnia, inhibited aromatase, reduced libido, impotence in men, and amenorrhoea, oligomenorrhea and infertility in women due to elevations in androgens. Studies have also shown that the resultant amenorrhea is due to hypercortisolism, which feeds back onto the hypothalamus resulting in decreased levels of GnRH release.
Many of the features of Cushing's are those seen in metabolic syndrome, including insulin resistance, hypertension, obesity, and elevated blood levels of triglycerides.
Cognitive conditions, including memory and attention dysfunctions, as well as depression, are commonly associated with elevated cortisol, and may be early indicators of exogenous or endogenous Cushing's. Depression and anxiety disorders are also common.
Other striking and distressing skin changes that may appear in Cushing's syndrome include facial acne, susceptibility to superficial fungus (dermatophyte and malassezia) infections, and the characteristic purplish, atrophic striae on the abdomen.
Other signs include increased urination (and accompanying increased thirst), persistent high blood pressure (due to cortisol's enhancement of epinephrine's vasoconstrictive effect) and insulin resistance (especially common with ACTH production outside the pituitary), leading to high blood sugar and insulin resistance which can lead to diabetes mellitus. Insulin resistance is accompanied by skin changes such as acanthosis nigricans in the axilla and around the neck, as well as skin tags in the axilla. Untreated Cushing's syndrome can lead to heart disease and increased mortality. Cortisol can also exhibit mineralocorticoid activity in high concentrations, worsening the hypertension and leading to hypokalemia (common in ectopic ACTH secretion) and hypernatremia (increased Na+ ions concentration in plasma). Furthermore, excessive cortisol may lead to gastrointestinal disturbances, opportunistic infections, and impaired wound healing related to cortisol's suppression of the immune and inflammatory responses. Osteoporosis is also an issue in Cushing's syndrome since osteoblast activity is inhibited. Additionally, Cushing's syndrome may cause sore and aching joints, particularly in the hip, shoulders, and lower back.
Brain changes such as cerebral atrophy may occur. This atrophy is associated with areas of high glucocorticoid receptor concentrations such as the hippocampus and correlates highly with psychopathological personality changes.
Additional symptoms may include:
Rapid weight gain Moodiness, irritability, or depression Muscle and bone weakness Memory and attention dysfunction Osteoporosis Diabetes mellitus Hypertension Immune suppression Sleep disturbances Menstrual disorders such as amenorrhea in women Infertility in women Impotence in men Hirsutism Baldness Hypercholesterolemia
Hyperpigmentation 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 pro-opiomelanocortin (POMC). Alternatively, it is proposed that the high levels of ACTH, β-lipotropin, and γ-lipotropin, which contain weak MSH function, can act on the melanocortin 1 receptor. A variant of Cushing's disease can be caused by ectopic, i.e. extra pituitary, ACTH production from, for example, a small-cell lung cancer.
When Cushing's syndrome is caused by an increase of cortisol at the level of the adrenal glands (via an adenoma or hyperplasia), negative feedback ultimately reduces ACTH production in the pituitary. In these cases, ACTH levels remain low and no hyperpigmentation develops.
Causes Cushing's syndrome may result from any cause of increased glucocorticoid levels, whether due to medication or internal processes. Some sources however do not consider the glucocorticoid medication-induced condition as "Cushing's syndrome" proper, instead using the term "Cushingoid" to describe the medication's side effects which mimic the endogenous condition.
Cushing's disease is a specific type of Cushing's syndrome caused by a pituitary tumor leading to excessive production of ACTH (adrenocorticotropic hormone). Excessive ACTH stimulates the adrenal cortex to produce high levels of cortisol, producing the disease state. While all Cushing's disease gives Cushing's syndrome, not all Cushing's syndrome is due to Cushing's disease.Lynnette K. Nieman, Beverly M. K. Biller, James W. Findling, John Newell-Price, Martin O. Savage, Paul M. Stewart, Victor M. Montori, The Diagnosis of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline, The Journal of Clinical Endocrinology & Metabolism, Volume 93, Issue 5, 1 May 2008, Pages 1526–1540, Several possible causes of Cushing's syndrome are known including the taking of herbal supplements over-the-counter that do not list glucocorticoids in their ingredients.
Exogenous The most common cause of Cushing's syndrome is the use of prescribed glucocorticoids to treat other diseases (iatrogenic Cushing's syndrome). Glucocorticoids are used in treatment of a variety of disorders, including asthma and rheumatoid arthritis, and also for immunosuppression after organ transplants. Administration of synthetic ACTH is also possible, but ACTH is less often prescribed due to cost and lesser utility. Rarely, Cushing's syndrome can also be due to the use of medroxyprogesterone acetate. In exogenous Cushing's, the adrenal glands may often gradually atrophy due to lack of stimulation by ACTH, the production of which is suppressed by glucocorticoid medication. Abruptly stopping the medication can thus result in acute and potentially life-threatening adrenal insufficiency and the dose must hence be slowly and carefully tapered off to allow internal cortisol production to pick up. In some cases, patients never recover sufficient levels of internal production and must continue taking glucocorticoids at physiological doses for life.
Cushing's syndrome in childhood is especially rare; it usually results from use of glucocorticoid medication.
Endogenous Endogenous Cushing's syndrome results from some derangement of the body's own system of cortisol secretion. Normally, ACTH is released from the pituitary gland when necessary to stimulate the release of cortisol from the adrenal glands.Le Tissier, P.R; Hodson, D.J; Lafont C; Fontanaud P; Schaeffer, M; Mollard, P. (2012) Anterior pituitary cell networks. Front Neuroendocrinol. Aug; 33(3):252-66
In pituitary Cushing's, a benign pituitary adenoma secretes ACTH. This is also known as Cushing's disease and is responsible for 70% of endogenous Cushing's syndrome.Cushing's Syndrome at The National Endocrine and Metabolic Diseases Information Service. July 2008. Citing: * In adrenal Cushing's, excess cortisol is produced by adrenal gland tumors, hyperplastic adrenal glands, or adrenal glands with nodular adrenal hyperplasia. Tumors outside the normal pituitary-adrenal system can produce ACTH (occasionally with CRH) that affects the adrenal glands. This etiology is called ectopic or paraneoplastic Cushing's disease and is seen in diseases such as small cell lung cancer. Finally, rare cases of CRH-secreting tumors (without ACTH secretion) have been reported, which stimulates pituitary ACTH production.
Pseudo-Cushing's syndrome Elevated levels of total cortisol can also be due to estrogen found in oral contraceptive pills that contain a mixture of estrogen and progesterone, leading to pseudo-Cushing's syndrome. Estrogen can cause an increase of cortisol-binding globulin and thereby cause the total cortisol level to be elevated. However, the total free cortisol, which is the active hormone in the body, as measured by a 24-hour urine collection for urinary free cortisol, is normal.
Pathophysiology The hypothalamus is in the brain and the pituitary gland sits just below it. The paraventricular nucleus (PVN) of the hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the pituitary gland to release adrenocorticotropin (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 CRH in the hypothalamus, which decreases the amount of ACTH released from the anterior pituitary gland.