Primary adrenal insufficiency (Addison's disease) is usually of what etiology?

Primary adrenal insufficiency, commonly known as Addison's disease, most often arises from autoimmune causes. In this condition, the body's immune system mistakenly targets and destroys the adrenal cortex, leading to insufficient production of adrenal hormones such as cortisol and aldosterone. Autoimmune adrenalitis is the most prevalent cause, reflecting a failure of immune tolerance and the development of adrenal-specific autoantibodies.

Other etiologies, while they can contribute to adrenal insufficiency, are less common. Viral infections can lead to adrenal damage but tend to be rare causes compared to autoimmune destruction. Tumors can also affect the adrenal glands but are typically associated with adrenal hyperfunction or can metastasize to the adrenal glands rather than directly causing primary adrenal insufficiency. Genetic mutations may cause congenital adrenal hyperplasia and other disorders but do not represent the typical cause in adult-onset primary adrenal insufficiency.

Overall, the autoimmune nature of Addison's disease accounts for the majority of cases, making it the most relevant etiology in clinical practice.