What is Addison's disease?
Anything that results in damage to the adrenal gland has the potential to cause the development of Addison's disease. Most commonly, the disorder is the result of an autoimmune malfunction, in which the body begins to react against its own tissue. The disorder may also result from adrenal cancers or infections. The prevalence rate is approximately 1 per 100,000 people.
The specific cause of the adrenal insufficiency may be either primary or secondary. In the case of primary adrenal insufficiency, the disorder arises directly within the outer region of the adrenal gland, called the adrenal cortex. Most of the time, the disorder is associated with an autoimmune dysfunction in which the body produces antibodies against adrenal tissue. Over time, the adrenal cortex is destroyed and the secretion of glucorticoid, mineralocorticoid, and adrenogenic hormones, the products of the adrenal cortex, ceases. Another cause of primary adrenal insufficiency is bacterial infections, particularly those associated with tuberculosis. The first identification of the disease, described by Thomas Addison in 1855, was associated with a tuberculosis infection in his patient. Other less common causes include fungal infections and malignancies.
Secondary adrenal insufficiency does not originate with the adrenal glands but rather is associated with abnormal regulation of adrenal hormone production, a function of the pituitary gland. Among the hormones produced within the pituitary gland is adrenocorticotropic hormone (ACTH), which stimulates glucocorticoid production by the adrenal cortex. Insufficient ACTH production results in a decrease in corticoid secretion. Any damage to the pituitary (or the hypothalamus, which actually regulates ACTH production by the pituitary) has the potential to affect ACTH production indirectly.
With Addison’s disease, the onset of symptoms is gradual and can easily be overlooked or misdiagnosed during the early stages of the disease. Initially, the person may exhibit extreme fatigue, low blood pressure, and loss of appetite. The person may faint upon standing. Severe diarrhea and vomiting are also common. As a result of salt loss, the person may crave salty foods. Severe expression of such symptoms is referred to as an Addisonian crisis; if untreated, it may be life-threatening. Because the production of ACTH itself is regulated by corticosteroid production in a feedback mechanism, reduced adrenal function results in increased levels of ACTH. This in turn can produce skin changes, particularly a darkening which mimics that of deep tanning. The presence of darkening equally over both exposed and unexposed skin can be indicative of Addison’s disease, particularly if other symptoms are also present.
A definitive diagnosis of Addison's disease is based upon a series of blood and urine tests. Patients may exhibit abnormally high levels of potassium, a potentially life-threatening situation, or a low level of sodium. More definitive tests measure the concentration of corticol hormones in the urine. Because ACTH production is controlled by corticosteroid concentrations, an increase in blood ACTH may also be observed. The definitive test begins with the intravenous injection of ACTH. Cortisol levels in the blood are then measured over a one-hour period. If cortisol levels do not change, this result is indicative of a likely adrenal insufficiency.
The treatment of Addison's disease generally involves replacing the hormones that the adrenal cortex is no longer manufacturing. Oral medication is available for most of these hormones, though dietary changes may also be necessary. For example, if the mineralocorticoid aldosterone is insufficient, resulting in a salt imbalance, then patients taking aldosterone supplements may also be advised to increase the salt content of their food.
Other forms of treatment may be symptomatic. If the patient suffers from low blood pressure or severe salt imbalances, conditions that are potentially life-threatening, then intravenous medication may be necessary.
As the monitoring of potassium and sodium levels is critical, it is generally recommended that patients routinely visit their physicians. It is important that a patient exhibiting symptoms of an Addisonian crisis (vomiting, diarrhea) receive immediate salt replacement and probably hydrocortisone as well.
Because secondary adrenal deficiency most often originates in the pituitary gland, the primary result is a decrease in ACTH production. In turn, the adrenal cortex is deficient only in the production of cortisol. Treatment generally involves the oral replacement of cortisol, often in the form of synthetic prednisone.
Addison's disease is a lifelong, chronic condition. While in the past it was often a life-threatening disorder, proper monitoring and hormone replacement can allow most people with the disease to live relatively normal lives with no restrictions. Because in most individuals the immediate cause is an autoimmune disorder, it is possible that eventually stem cell research, along with improved methods of controlling autoimmune phenomena, will provide a means for replacing adrenal tissue.
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