Summary
Highlights
Addison's disease is characterized by the insufficiency of all hormones produced by the adrenal cortex. It is often considered the opposite of Cushing's disease. Understanding the anatomy and physiology of the adrenal cortex is crucial, starting with the brain's hypothalamus and pituitary gland, which regulate adrenal hormone production.
The hypothalamus releases corticotropin-releasing hormone (CRH), stimulating the anterior pituitary to secrete adrenocorticotropic hormone (ACTH). ACTH then stimulates the adrenal cortex to produce three main types of hormones: mineralocorticoids (like aldosterone), glucocorticoids (like cortisol), and androgens. These hormones play vital roles in blood pressure regulation, metabolism, immune response, and secondary sexual characteristics.
Addison's disease is primarily caused by autoimmune destruction of the adrenal cortex, leading to decreased production of mineralocorticoids, glucocorticoids, and androgens. This results in symptoms such as low blood pressure, tachycardia, weight loss, skin pigmentation, fatigue, and decreased libido.
While autoimmune causes account for 70% of cases, other causes include infections (e.g., tuberculosis), adrenal malignancies, hemorrhage, infiltrative diseases, iatrogenic causes (adrenalectomy), congenital adrenal hyperplasia, and certain medications. Risk factors include female gender, existing autoimmune diseases, and adrenal hemorrhage.
Investigations for Addison's disease involve checking serum ACTH levels (which will be increased due to lack of negative feedback from cortisol) and presence of adrenal autoantibodies. Blood tests may reveal hyponatremia, hyperkalemia, and increased urea. Imaging like CT scans can identify adrenal tumors or hemorrhage, and thyroid function tests help differentiate from Graves' disease.
Management of Addison's disease involves lifelong hormone replacement therapy with glucocorticoids (hydrocortisone) and mineralocorticoids (fludrocortisone), and sometimes androgen replacement for females. Patient education on medication adherence is crucial to prevent adrenal crisis, a life-threatening condition caused by a sudden drop in glucocorticoid levels. Over-replacement can lead to secondary Cushing's syndrome, osteoporosis, and hypertension.