From the June 1998 Newsletter:
Some of our members who have been diagnosed with Secondary Addison’s disease were under the impression that the "Secondary" meant they had a minor form of Addison’s disease. This is certainly not the case. The difference between Primary and Secondary Addison’s disease is the cause of the lack of cortisol.
Primary Addison’s disease results when the Adrenal Glands have "packed it in" usually as a result of an autoimmune disorder, and less commonly caused by tuberculosis, chronic infections, cancer, and surgical removal of the adrenal glands. Patients with Primary Addison’s, before they are diagnosed and treated, have high levels of ACTH and usually skin pigmentation.
Secondary Addison’s Disease on the other hand is due to problems with Hypothalamus/Pituitary Glands causing a lack of ACTH which results in a drop in the adrenal glands production of cortisol but not aldosterone. It can result from the surgical removal of benign, non-cancerous, ACTH-producing tumours of the pituitary gland (Cushing’s disease) or less commonly from damage to pituitary gland as a result of tumours or infections, loss of blood flow to the pituitary, radiation for the treatment of pituitary tumours or surgical removal of parts of the hypothalamus or the pituitary gland during neurosurgery or these areas.
A temporary form of secondary adrenal insufficiency may occur when a person who has been taking glucocorticoids like prednisone (commonly used to treat illnesses like asthma, rheumatoid arthritis or ulcerative colitis) for a long time stops taking the medication. Glucocorticoid hormones block the release of both ACTH and CRH (corticotropin-releasing hormone). If the CRH levels drop, the pituitary is not stimulated to release ACTH, resulting in the adrenal glands not secreting sufficient levels of cortisol.
Those with Secondary Addison’s disease are more tolerant to metabolic stress because the mineralocorticoids are intact.