Adrenal hypofunction or Addison’s disease is a rare condition but is simple to treat once diagnosed. It can arise from one of a number of causes: an autoimmune destruction of the adrenal cortex, as a response to tuberculosis (TB), amyloidosis, hemochromatosis, following adrenalectomy or hypo-thalamic or pituitary diseases referred to as secondary adrenal insufficiency. Addison’s disease is characterized by a deficiency of glucocorticoids and mineralocorticoids. Its clinical features include weakness, lethargy, anorexia, nausea, vomiting, weight loss, hypotension, skin pigmentation, hypoglycemia and depression (Figure 7.30). In the first few months, symptoms are usually vague with only lethargy, weakness and weight loss presenting as a result of glucocorticoid deficiency. Later, patients start to vomit and have abdominal pain. The lack of mineralocorticoids leads to an excessive loss of Na+ and therefore hypotension is common in these patients. Plasma ACTH is increased because of pituitary response to low levels of cortisol given the lack of a negative feedback mechanism. Adrenocorticotrophic hormone can stimulate melanocytes in skin to produce the melanin, hence pigmentation is a common feature in Addison’s disease.
A clinical suspicion of Addison’s disease can be confirmed by demonstrating hyperkalemia with hyponatremia . The plasma cortisol is usually, but not always, low in these patients. A high concentration of ACTH coupled with a low concentration of cortisol is indicative of Addison’s disease whereas low cortisol and ACTH values are suggestive of secondary adrenal insufficiency. The situation can be resolved using complex biochemical tests with the analog of ACTH, synacthen. The short synacthen test involves an intramuscular injection of 0.25 mg of synacthen. The concentration of plasma cortisol is measured within 30 min. If it rises by at least 200 or to a value greater than 550 nmol dm–3, then Addison’s disease is unlikely. If this is not the case, then it is appropriate to proceed to the long synacthen test which involves an intramuscular injection of 1 mg of ACTH daily for three days. On the fourth day, the short synacthen test is performed and the serum concentration of cortisol is measured. If this is less than 200 nmol dm–3 with no increase following administration of synacthen there is primary adrenal failure and the patient is suffering from Addison’s disease. If, however, there is an incremental increase of at least 200 nmol dm–3 above the baseline, then the decreased output of cortisol from adrenal gland is secondary and due to a deficiency of ACTH caused by a hypothalamic or pituitary disorder. Once Addison’s disease is diagnosed, it is necessary to ascertain its cause. A number of laboratories test for the presence of antibodies against the adrenal glands to see if there is an autoimmune cause. A plain abdominal X-ray may be useful in that it can detect calcification of adrenal glands as a result of TB .
The conventional therapy for Addison’s disease involves treatment with steroids, such as hydrocortisone and fludrocortisone, which possess glucocorticoid and mineralocorticoid activities respectively. If a patient is left untreated he or she will eventually experience an adrenal crisis precipitated by stress, bacterial infection, trauma or surgery, which is a medical emergency. Typical clinical features of a crisis are abdominal pain, vomiting, hypotension together with hyponatremia, hypoglycemia and hyperkalemia. Its treatment involves administering saline infusions to correct the hypotension, fluid and salt losses and intravenous steroids to correct glucocorticoid and mineralocorticoid deficiencies. The precipitating factors, such as bacterial infections, require identification and appropriate treatment.
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