Addison's disease, also known as chronic adrenal insufficiency, or hypocortisolism, is a rare endocrine and hormonal disorder. It occurs when abnormally low quantities of all the adrenal steroid hormones are produced by the adrenal gland. Addison's disease usually follows the autoimmune destruction of the adrenal cortex (outer layer of the adrenal gland), in which the immune system creates antibodies against the body's own tissues. The adrenal glands, seated above the kidneys, fail to produce enough of the hormone cortisol and, sometimes, the hormone aldosterone.
In Addison's disease, the complex coordination of the human body and endocrine system is broken down, but may not be noticed until the presence of a physically stressful situation. Thus Addison's disease highlights the normally complex and harmonious coordination of the human body and endocrine system. Stress on the body from another disease, such as tuberculosis, cancer, or AIDS, impacts the output of hormones from the adrenal glands, manifesting in Addison's disease. Or the autoimmune system, which normally protects the body against disease, can turn against the adrenal cortex, manifesting this disease. The disruption of one bodily function thus results in a cascading effect of symptoms.
The disease occurs in all age groups and afflicts men and women equally. It is estimated that the disease affects about 1 to 2 per 100,000 people. British physician Dr. Thomas Addison first described the disease in his 1849 publication, On the Constitutional and Local Effects of Disease of the Suprarenal Capsules. The disease has also been identified in other mammals, such as dogs and cats.
Addison's disease refers specifically to primary adrenal insufficiency, in which the adrenal glands themselves malfunction. Secondary adrenal insufficiency, which is not considered Addison's disease, occurs when the anterior pituitary gland does not produce enough adrenocorticotropic hormone (ACTH) to adequately stimulate the adrenal glands.
Addison's disease is far less common than Cushing's syndrome, which is also a disease of the adrenal cortex.
Addison's disease progresses slowly and symptoms may not present or be noticed until some stressful illness or situation occurs. Common symptoms are:
An illness or accident can aggravate the adrenal problems and cause an Addisonian crisis, also known as acute adrenal insufficiency. However, the most common cause is discontinuing corticosteroid therapy without tapering the dose. Symptoms that may occur include:
If left untreated, an Addisonian crisis can be fatal. It is considered a medical emergency.
In its early stages, adrenal insufficiency can be difficult to diagnose. In suspected cases of Addison's disease, low adrenal hormone levels must be demonstrated followed by the establishment of the cause.
The ACTH/ stimulation test is the most specific test for diagnosing Addison's disease. In this test, blood cortisol, urine cortisol, or both are measured before and after a synthetic form of ACTH is given by injection. In the so-called short, or rapid, ACTH test, measurement of cortisol in the blood is repeated 30 to 60 minutes after an intravenous ACTH injection. The normal response after an injection of ACTH is a rise in blood and urine cortisol levels. Patients with either form of adrenal insufficiency respond poorly or do not respond at all.
When the response to the short ACTH test is abnormal, a "long" CRH stimulation test is required to determine the cause of adrenal insufficiency. In this test, synthetic corticotropin-releasing hormone (CRH) is injected intravenously and blood cortisol is measured before and 30, 60, 90, and 120 minutes after the injection. Patients with primary adrenal insufficiency have high ACTHs but do not produce cortisol. Patients with secondary adrenal insufficiency have deficient cortisol responses but absent or delayed ACTH responses. Absent ACTH response points to the pituitary as the cause; a delayed ACTH response points to the hypothalamus as the cause.
Once a diagnosis of primary adrenal insufficiency has been made, x-ray exams of the abdomen may be taken to see if the adrenals have any signs of calcium deposits. Calcium deposits may indicate tuberculosis. A tuberculin skin test also may be used. If secondary adrenal insufficiency is the cause, doctors may use different imaging tools to reveal the size and shape of the pituitary gland. The most common is the CT scan, which produces a series of x-ray pictures giving a cross-sectional image of a body part.
Seventy percent of cases of Addison's disease are said to be due to autoantibodies directed against adrenal cells containing 21-hydroxylase, an enzyme involved in the production of cortisol and aldosterone. Adrenal insufficiency occurs when at least 90 percent of the adrenal cortex has been destroyed. As a result, often both glucocorticoid (cortisol) and mineralocorticoid (aldostertone) hormones are lacking. Sometimes only the adrenal gland is affected, as in idiopathic adrenal insufficiency; sometimes other glands also are affected, as in the polyendocrine deficiency syndrome.
The syndrome is classified into two separate forms, type I and type II. In type I, which occurs in children, the adrenal insufficiency may be accompanied by underactive parathyroid glands (hypothyroidism), slow sexual development, pernicious anemia, chronic candida infections, chronic active hepatitis, and alopecia (hair loss). Type II features include an hypothyroidism, slow sexual development, diabetes (type I), and vitiligo, which is the loss of pigment from various areas of the skin. Type II tends to afflict young adults and is often called Schmidt's syndrome.
Twenty percent of cases of Addison's disease and primary adrenal insufficiency are due to tuberculosis, or TB. Although TB was a major cause of the disease in the nineteenth century, when Addison's disease was first discovered, its role has decreased remarkably due to better treatment for TB.
The remainder of cases are due to HIV, sarcoidosis (a disease characterized by the formation of granulomatous lesions that appear especially in the liver, lungs, skin, and lymph nodes; also called sarcoid), amyloidosis (a disorder marked by the deposition of amyloid in various organs and tissues of the body; may be associated with a chronic disease such as rheumatoid arthritis, tuberculosis, or multiple myeloma), hemochromatosis, metastatic cancer to the adrenal glands, adrenal hemorrhage (profuse bleeding), Waterhouse-Friderichsen syndrome (massive, usually bilateral, hemorrhage into the adrenal glands caused by fulminant meningococcemia), and congenital adrenal hyperplasia.
Treatment for Addison's disease involves replacing the lacking cortisol and, if necessary, fludrocortisone as a replacement for the missing aldosterone. Caution must be exercised when a person with Addison's disease faces a stressful situation, such as surgery or pregnancy.
Addison's disease has been diagnosed in both domesticated mammals (cats, dogs, and sheep) and wild mammals (otters). In cats, it is quite rare. It is more commonly diagnosed in dogs, although still uncommon. Among breeds of dogs, it is more prominent in mixed breeds, German shepherds, labrador retrievers, rottweilers, and standard and miniature poodles (Lorenz and Melendez 2006). In dogs, the disease is inherited via the female line, possibly due to autoimmune antibodies in the milk. It is more common in female dogs (68 percent of cases) and in dogs less than 5 years old (Lorenz and Melendez 2006).
The first sign of Addison's disease in dogs is a much longer urinating period than normal. Urine is very light and pressure while urinating is lower than usual. When the dog loses its appetite and changes its temperament, a blood test should be taken as soon as possible. Depression, anorexia, weight loss, vomiting, diarrhea, gastrointestinal hemorrhage, and mild abdominal pain may also be clinical signs of the disease (Lorenz and Melendez 2006).
Addison's disease is treated with Prednisolone and Florinef, which are taken twice a day after meals. The medications increase thirst and water input as well as increase urine output. An alternative to oral Florinef is a monthly injection called Percorten V, whose active ingredient is desoxycorticosterone pivalate, or DOCP. The amounts of the medicines taken depend on the weight of the individual dog. Blood samples need to be taken after every 3-4 months, regardless of how the dog feels, to make sure the dog's condition is stable.
Stress levels, both positive and negative, of an ill dog must be kept to a minimum. A dog's relaxing pulse reading should be known so that a stressful event can be identified by an increased pulse reading. If an owner of an ill dog knows about an upcoming stressful situation, such as a show or traveling, he or she can give a larger does of medicine.
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