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|Classification and external resources|
|Classification and external resources|
Addison’s disease (also Addison disease, chronic adrenal insufficiency, hypocortisolism, and hypoadrenalism) is a rare, chronic endocrine disorder in which the adrenal glands do not produce sufficient steroid hormones (glucocorticoids and often mineralocorticoids). It is characterised by a number of relatively nonspecific symptoms, such as abdominal pain and weakness, but under certain circumstances, these may progress to Addisonian crisis, a severe illness which may include very low blood pressure and coma.
The condition arises from problems with the adrenal gland, primary adrenal insufficiency, and can be caused by damage by the body's own immune system, certain infections, or various rarer causes. Addison's disease is also known as chronic primary adrenocortical insufficiency, to distinguish it from acute primary adrenocortical insufficiency, most often caused by Waterhouse-Friderichsen syndrome. Addison's disease should also be distinguished from secondary and tertiary adrenal insufficiency, which are caused by deficiency of ACTH (produced by the pituitary gland) and CRH (produced by the hypothalamus), respectively. Despite this distinction, Addisonian crises can happen in all forms of adrenal insufficiency.
Addison's disease and other forms of hypoadrenalism are generally diagnosed via blood tests and medical imaging. Treatment involves replacing the absent hormones (oral hydrocortisone and fludrocortisone). Lifelong, continuous steroid replacement therapy is required, with regular follow-up treatment and monitoring for other health problems.
Addison’s disease is named after Dr. Thomas Addison, the British physician who first described the condition in 1849. The adjective "Addisonian" is used to describe features of the condition, as well as patients suffering from Addison’s disease.
The symptoms of Addison's disease develop insidiously and may take time to be recognised. The most common symptoms are fatigue, lightheadedness upon standing or while upright, muscle weakness, fever, weight loss, difficulty in standing up, anxiety, nausea, vomiting, diarrhea, headache, sweating, changes in mood and personality, and joint and muscle pains. Some have marked cravings for salt or salty foods due to the urinary losses of sodium. Hyperpigmentation of the skin may be noted, particularly in sun-exposed areas, as well as darkening of the palmar creases, sites of friction, recent scars, the vermilion border of the lips, and genital skin. This is not encountered in secondary and tertiary hypoadrenalism.
On physical examination, the following may be noticed:
An "Addisonian crisis" or "adrenal crisis" is a constellation of symptoms that indicates severe adrenal insufficiency. This may be the result of either previously undiagnosed Addison's disease, a disease process suddenly affecting adrenal function (such as adrenal hemorrhage), or an intercurrent problem (e.g. infection, trauma) in someone known to have Addison's disease. It is a medical emergency and potentially life-threatening situation requiring immediate emergency treatment.
Characteristic symptoms are:
Causes of adrenal insufficiency can be categorized by the mechanism through which they cause the adrenal glands to produce insufficient cortisol. These are adrenal dysgenesis (the gland has not formed adequately during development), impaired steroidogenesis (the gland is present but is biochemically unable to produce cortisol) or adrenal destruction (disease processes leading to glandular damage).
All causes in this category are genetic, and generally very rare. These include mutations to the SF1 transcription factor, congenital adrenal hypoplasia (CAH) due to DAX-1 gene mutations and mutations to the ACTH receptor gene (or related genes, such as in the Triple A or Allgrove syndrome). DAX-1 mutations may cluster in a syndrome with glycerol kinase deficiency with a number of other symptoms when DAX-1 is deleted together with a number of other genes.
To form cortisol, the adrenal gland requires cholesterol, which is then converted biochemically into steroid hormones. Interruptions in the delivery of cholesterol include Smith-Lemli-Opitz syndrome and abetalipoproteinemia.
Of the synthesis problems, congenital adrenal hyperplasia is the most common (in various forms: 21-hydroxylase, 17α-hydroxylase, 11β-hydroxylase and 3β-hydroxysteroid dehydrogenase), lipoid CAH due to deficiency of StAR and mitochondrial DNA mutations. Some medications interfere with steroid synthesis enzymes (e.g. ketoconazole), while others accelerate the normal breakdown of hormones by the liver (e.g. rifampicin, phenytoin).
Autoimmune adrenalitis is the most common cause of Addison's disease in the industrialised world. Autoimmune destruction of the adrenal cortex is caused by an immune reaction against the enzyme 21-hydroxylase (a phenomenon first described in 1992). This may be isolated or in the context of autoimmune polyendocrine syndrome (APS type 1 or 2), in which other hormone-producing organs, such as the thyroid and pancreas, may also be affected.
Adrenal destruction is also a feature of adrenoleukodystrophy (ALD), and when the adrenal glands are involved in metastasis (seeding of cancer cells from elsewhere in the body, especially lung), hemorrhage (e.g. in Waterhouse-Friderichsen syndrome or antiphospholipid syndrome), particular infections (tuberculosis, histoplasmosis, coccidioidomycosis), or the deposition of abnormal protein in amyloidosis.
Use of high-dose steroids for more than a week begins to produce suppression of the patient's adrenal glands because the exogenous glucocorticoids suppress hypothalamic corticotropin-releasing hormone (CRH) and pituitary adrenocorticotropic hormone (ACTH). With prolonged suppression, the adrenal glands atrophy (physically shrink), and can take months to recover full function after discontinuation of the exogenous glucocorticoid. During this recovery time, the patient is vulnerable to adrenal insufficiency during times of stress, such as illness.
Routine investigations may show:
In suspected cases of Addison's disease, demonstration of low adrenal hormone levels even after appropriate stimulation (called the ACTH stimulation test) with synthetic pituitary ACTH hormone tetracosactide is needed for the diagnosis. Two tests are performed, the short and the long test. It should be noted that dexamethasone does not cross-react with the assay and can be administered concomitantly during testing.
The short test compares blood cortisol levels before and after 250 micrograms of tetracosactide (intramuscular or intravenous) is given. If, one hour later, plasma cortisol exceeds 170 nmol/l and has risen by at least 330 nmol/l to at least 690 nmol/l, adrenal failure is excluded. If the short test is abnormal, the long test is used to differentiate between primary adrenal insufficiency and secondary adrenocortical insufficiency.
The long test uses 1 mg tetracosactide (intramuscular). Blood is taken 1, 4, 8, and 24 hr later. Normal plasma cortisol level should reach 1000 nmol/l by 4 hr. In primary Addison's disease, the cortisol level is reduced at all stages, whereas in secondary corticoadrenal insufficiency, a delayed but normal response is seen.
Other tests may be performed to distinguish between various causes of hypoadrenalism, including renin and adrenocorticotropic hormone levels, as well as medical imaging - usually in the form of ultrasound, computed tomography or magnetic resonance imaging.
Adrenoleukodystrophy, and the milder form, adrenomyeloneuropathy, cause adrenal insufficiency combined with neurological symptoms. These diseases are estimated to be the cause of adrenal insufficiency in about 35% of male patients with idiopathic Addison’s disease, and should be considered in the differential diagnosis of any male with adrenal insufficiency. Diagnosis is made by a blood test to detect very long chain fatty acids.
Treatment for Addison's disease involves replacing the missing cortisol, sometimes in the form of hydrocortisone tablets, or prednisone tablets in a dosing regimen that mimics the physiological concentrations of cortisol. Alternatively, one-quarter as much prednisolone may be used for equal glucocorticoid effect as hydrocortisone. Treatment is usually lifelong. In addition, many patients require fludrocortisone as replacement for the missing aldosterone. Caution must be exercised when persons with Addison's disease become unwell with infection, have surgery or other trauma, or become pregnant. In such instances, their replacement glucocorticoids, whether in the form of hydrocortisone, prednisone, prednisolone, or other equivalent, often must be increased. Inability to take oral medication may prompt hospital admission to receive steroids intravenously. People with Addison's are often advised to carry information on them (e.g., in the form of a MedicAlert bracelet) for the attention of emergency medical services personnel who might need to attend to their needs.
Standard therapy involves intravenous injections of glucocorticoids and large volumes of intravenous saline solution with dextrose (glucose). This treatment usually brings rapid improvement. When the patient can take fluids and medications by mouth, the amount of glucocorticoids is decreased until a maintenance dose is reached. If aldosterone is deficient, maintenance therapy also includes oral doses of fludrocortisone acetate.
The frequency rate of Addison's disease in the human population is sometimes estimated at roughly one in 100,000. Some research and information sites put the number closer to 40-60 cases per million population. (1/25,000-1/16,600) (Determining accurate numbers for Addison's is problematic at best and some incidence figures are thought to be underestimates.) Addison's can afflict persons of any age, gender, or ethnicity, but it typically presents in adults between 30 and 50 years of age. Research has shown no significant predispositions based on ethnicity.
With proper medication, especially hormone replacement therapy, patients can expect to live relatively normal lives.
People with adrenal insufficiency should always carry identification stating their condition in case of an emergency. The card should alert emergency personnel about the need to inject 100 mg of cortisol if its bearer is found severely injured or unable to answer questions. The card should also include the doctor's name and telephone number and the name and telephone number of the nearest relative to be notified.
When traveling, a needle, syringe, and an injectable form of cortisol should be carried for emergencies. A person with Addison's disease also should know how to increase medication during periods of stress or mild upper respiratory infections. Immediate medical attention is needed when severe infections, vomiting, or diarrhea occurs, as these conditions can precipitate an Addisonian crisis. A patient who is vomiting may require injections of hydrocortisone, since oral hydrocortisone supplements cannot be adequately metabolised.
Addison’s disease is named after Dr. Thomas Addison, the British physician who first described the condition in On the Constitutional and Local Effects of Disease of the Suprarenal Capsules (1849). All of Addison's six original patients had tuberculosis of the adrenal glands. While Addison's six patients in 1855 all had adrenal tuberculosis, the term "Addison's disease" does not imply an underlying disease process.
The condition was initially considered a form of anemia associated with the adrenal glands. Because little was known at the time about the adrenal glands (then called "Supra-Renal Capsules"), Dr. Addison’s monograph describing the condition was an isolated insight. As the adrenal function became better known, Dr. Addison’s monograph became known as an important medical contribution and a classic example of careful medical observation.
The condition has been diagnosed in all breeds of dogs. In general, it is underdiagnosed, and one must clinically suspect it as an underlying disorder for many presenting complaints. Females are overrepresented, and the disease often appears in middle age (4–7 yr), although any age or either gender may be affected. Genetic continuity between dogs and humans helps to explain the occurrence of Addison's disease in both species.
Hypoadrenocorticism is treated with fludrocortisone or a monthly injection called Percorten V (desoxycorticosterone pivlate (DOCP)) and prednisone. Routine blood work is necessary in the initial stages until a maintenance dose is established. Most of the medications used in the therapy of hypoadrenocorticism cause excessive thirst and urination, making it important to provide enough drinking water. If the owner knows about an upcoming stressful situation (shows, traveling, etc.), patients generally need an increased dose of prednisone to help deal with the added stress. Avoidance of stress is important for dogs with hypoadrenocorticism.
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