Adrenal insufficiency refers to an endocrine disorder resulting from a reduced production or the decreased action of hormones by the adrenal gland, mainly the steroid hormones. Symptoms primarily result from lack of mineralocorticoids and/or glucocorticoids and this condition may be triggered by lesions of the adrenal glands themselves or by pathologies of superior regulatory centers.
Healthy adrenal glands release a variety of hormones, namely mineralocorticoids, glucocorticoids, estrogen, progesterone, and catecholamines. Adrenal insufficiency (AI) may refer to a reduced production of either or all of those hormones, and this condition may be provoked by distinct diseases. On the one hand, pathologies may directly affect adrenal tissues and thus interfere with hormone synthesis. This form of AI is deemed primary AI and may also be referred to as Addison's disease. Most cases of primary AI are the result of an autoimmune disease. On the other hand, the adrenal glands form part of the complex endocrine network and are subjected to regulatory mechanisms. Thus, functional impairment of superior centers may be associated with an inadequate stimulation of adrenal hormone synthesis. In detail, lesions of the pituitary gland may cause secondary AI, lesions of the hypothalamus may trigger tertiary AI. Therapy is mainly symptomatic and consists in life-long supplementation of mineralocorticoids and glucocorticoids. If the underlying disease is curable, the patient's prognosis improves.
AI is a general term that may refer to distinct entities.
Patients may suffer from primary AI, i.e., dysfunction of the adrenal glands results in a decreased production of adrenal hormones. Generally, this form of AI comprises all zones of the adrenal cortex and the adrenal medulla and thus, patients suffer from both mineralocorticoid and glucocorticoid deficiencies. Possible causes of primary AI are adrenal dysgenesis, congenital adrenal hyperplasia due to hereditary enzyme deficiencies, ACTH resistance syndromes, metabolic disorders interfering with cholesterol synthesis or peroxisomal function, isolated autoimmune adrenalitis, autoimmune polyendocrinopathy, infectious diseases like tuberculosis, adrenal infarction, adrenal hemorrhage, trauma, neoplasms, drug-induced AI and surgical resection . Of note, clinical symptoms may only manifest after the destruction of the vast majority of adrenal tissue .
Secondary and tertiary AI are provoked by lesions of superior centers. Both glucocorticoid- and androgen-producing cells form part of the hypothalamic-pituitary-adrenal hormone axis, i.e., the corresponding subpopulations of adrenal cells depend on the release of corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH) by the hypothalamus and the anterior pituitary gland, respectively. The hypothalamic and pituitary function may be impaired by ischemia or stroke, inflammation, and/or infection, trauma, benign and malignant neoplasms, long-term administration of glucocorticoids and irradiation of the brain, among others. In contrast, mineralocorticoid release is not affected by CRH and ACTH levels but is regulated by the renin-angiotensin system. Thus, individuals affected by secondary or tertiary AI don't develop mineralocorticoid deficiency.
Of note, partial dysfunction of the adrenal glands is also observed in pathologies that are usually not considered forms of AI. For instance, the adrenogenital syndrome is caused by a gene defect resulting in reduced adrenal glucocorticoid synthesis, consequently increased ACTH levels, and an excess stimulation of adrenal androgen production . Isolated hypoaldosteronism is rare but may occur in patients suffering from chronic idiopathic hypoaldosteronism, familial corticosterone methyl oxidase deficiencies, persistent hypotension or conditions associated with reduced renin secretion .
Autoimmune-mediated AI is the most common form of the disease and its prevalence has been estimated to 1 in 10,000 people. Congenital adrenal hyperplasia is diagnosed in 1 per 15,000 life births, and about 1 in 20,000 men suffers from X-linked adrenoleukodystrophy . The annual incidence of primary AI has been stated to be <1 in 100,000 inhabitants of western Norway, and this condition is most frequently diagnosed during the fourth decade of life. Of note, symptom onset of congenital adrenal hyperplasia and X-linked adrenoleukodystrophy typically occurs in infancy or childhood .
AI due to disturbances of the hypothalamic-pituitary-adrenal hormone axis is more common than primary AI affects up to 28 per 100,000 people and is most commonly a side effect of prolonged glucocorticoid therapy . Women are affected more often than men. Contrary to primary AI, it is usually diagnosed in the elderly.
The adrenal cortex encapsulates the adrenal medulla and consists of three layers denominated zona glomerulosa, zona fasciculata, and zona reticularis. Distinct subpopulations of adrenal cells produce hormones that affect electrolyte balance, carbohydrate metabolism, growth and sexual characteristics, as well as autonomous functions. In detail, the following hormones originate from the adrenal glands:
AI is primarily associated with disturbances of electrolyte balance and carbohydrate metabolism, since deficiencies in adrenal androgen and catecholamine production are largely compensated by the testes, chromaffin paraganglia, and the sympathetic nervous system, respectively.
Aldosterone acts on renal tubular epithelial cells, mucous membranes of the intestinal tract, salivary and sweat glands. It favors the excretion of potassium and protons and stimulates the reabsorption of sodium, chloride, and water in distal tubules of the kidneys by inducing an up-regulation of ion channel and Na+-K+-ATPase expression. Consequently, patients suffering from AI with mineralocorticoid deficiency develop hyperkalemia, metabolic acidosis, hyponatremia, hypochloremia, and hypovolemia.
Glucocorticoid release provokes an increase of serum glucose levels by enhancing hepatic gluconeogenesis and induction of peripheral insulin resistance. At the same time, glucocorticoids favor protein and lipid catabolism. Lack of glucocorticoids thus leads to hypoglycemia, insulin sensitivity, and weight loss. Of note, ACTH secretion is physiologically reduced by glucocorticoids, but this negative feedback loop is interrupted in AI. Thus, pituitary ACTH synthesis is permanently elevated and this condition results in increased levels of the melanocyte-stimulating hormone, which originates from the same precursor (proopiomelanocortin; POMC). Therefore, AI patients develop hyperpigmentation of the skin.
Patients suffering from AI require life-long therapy unless the underlying condition is curable. In the case of non-compliance with therapeutic regimens or if left untreated, an acute metabolic decompensation may result in fatal adrenal crisis. Despite optimum therapy, the annual incidence of adrenal crisis in patients suffering from primary AI has been estimated to be about 8%, while this life-threatening complication is less frequently observed in secondary or tertiary AI . Recently, Norwegian researchers found young AI patients to have an increased mortality due to adrenal failure, infection, and sudden death . Otherwise, AI patients have an excellent prognosis.
Patients may present with rather non-specific symptoms or be admitted for emergency care because of an adrenal crisis. With regards to the former, symptoms develop gradually and comprise fatigue, lethargy, generalized weakness, gastrointestinal complaints, loss of appetite and weight, and hypotension. Depending on its severity, the latter may manifest in form of orthostatic hypotension or prolonged dizziness and syncopes. Patients may experience mood swings and behavioral disorders. Hyperpigmentation is common in patients suffering from primary AI, is of great diagnostic value, and is primarily noted in sun-exposed areas. Additional symptoms may result from mineralocorticoid deficiency - affected individuals frequently report to crave salt - and lack of androgens in females, which may cause delayed pubarche and reduced libido. Secondary AI may be accompanied by other endocrine disorders resulting from panhypopituitarism or more extensive lesions of the hypothalamus.
The adrenal or Addisonian crisis is a life-threatening condition most commonly observed in individuals affected by primary AI. Patients may present with severe hypotension leading to reduced levels of consciousness and shock, with acute-onset high fever, nausea, vomiting and abdominal pain. Myalgia and arthralgia may also be experienced.
Laboratory analyses of blood samples typically yield the following results:
Further, workup aims at identifying the cause of hypoglycemia and electrolyte imbalances and may comprise these measures :
Hormone replacement is the mainstay of long-term AI therapy. A thorough workup is required to assess the degree of mineralocorticoid and glucocorticoid deficiency in individual patients, who should undergo regular follow-ups to allow for a precise adjustment of doses. In general, medication should be dosed as high as necessary and as low as possible .
Treatment of Addisonian crisis should be initiated immediately and comprises of high-dosed intravenous application of hydrocortisone, glucose, and saline solution. Detailed recommendations are also available .
Long-term administration of glucocorticoids should be avoided; if required, doses should be maintained as low as possible. Further measures can be undertaken to avoid traumatic lesions of the adrenal glands, pituitary gland, and hypothalamus; excision during retroperitoneal and head surgery; and infectious diseases that may affect these endocrine organs. No specific measures can be recommended to prevent autoimmune-mediated AI.
The adrenal glands are endocrine organs located in close proximity to the kidneys. They are composed of distinct subpopulations of cells which release hormones that affect electrolyte balance, carbohydrate metabolism, growth and sexual characteristics, as well as autonomous function. If an individual suffers from adrenal insufficiency (AI), adrenal hormone production is partially or completely impaired. Since the adrenal glands form part of the complex endocrine network, they are subjected to regulatory mechanisms. Therefore, AI may not only result from a dysfunction of adrenal tissue (e.g., due to developmental or gene defects, or owing to destruction of the adrenal glands in an immune reaction directed against endogenous tissues), but also from lesions of superior centers. Those superior centers are located within or close to the brain and may be affected by stroke, trauma, tumors and other pathologies. Furthermore, regulatory mechanisms may be overridden if certain drugs, mainly glucocorticoids, are administered over long periods of time.
AI patients typically experience fatigue, lethargy, generalized weakness, hypotension, postural dizziness, nausea, vomiting and diarrhea, loss of appetite and weight, and hyperpigmentation. Laboratory analyses of blood samples typically reveal hyponatremia, hypochloremia, hyperkalemia, and metabolic acidosis. In order to prevent so-called adrenal crisis, which are life-threatening events resulting from an acute metabolic decompensation, missing hormones have to be supplemented. Accordingly, affected individuals require life-long therapy with fludrocortisone and/or hydrocortisone. Compliance with therapeutic regimens provided, AI patients have an excellent prognosis.