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:

• Hypoglycemia due to corticosteroid deficiency
• Metabolic acidosis due to mineralocorticoid deficiency, furthermore
• Hyponatremia
• Hypochloremia
• Hyperkalemia

Further, workup aims at identifying the cause of hypoglycemia and electrolyte imbalances and may comprise these measures [5]:

• Conduction of an ACTH stimulation test, i.e., determination of serum cortisol levels before and after intravenous administration of synthetic ACTH. Observation of an inadequate cortisol response is consistent with AI but does not allow for a distinction between primary AI and AI due to lesions of superior centers.
• Assessment of serum ACTH concentrations. Enhanced levels of ACTH are observed in primary AI, while secondary or tertiary AI is associated with ACTH deficiency.
• Screening for autoantibodies directed against the adrenal tissue.
• Diagnostic imaging to visualize neoplasms infiltrating the adrenal glands, the pituitary gland or the hypothalamus (computed tomography scans and magnetic resonance imaging).
• Screening for gene defects known to be associated with AI.

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 [11].

• Prescription of fludrocortisone is indicated in patients suffering from aldosterone deficiency. Children should receive daily doses of 0.025 to 0.2 mg per day, adults are prescribed 0.05 to 0.2 mg per day [9].
• To compensate for glucocorticoid deficiency, adult patients are generally administered 15-25 mg hydrocortisone daily [9]. Lower doses are indicated in pediatric patients and should be based on height, weight and body surface [Park]. Under physiological conditions, glucocorticoid secretion is highest in the morning and thus, about half of the total daily dose should be administered at this time of the day. The remaining dose of hydrocortisone may be given in another two applications. Because AI patients show an inadequate cortisol response to environmental factors, it may be necessary to augment hydrocortisone dosage in periods of stress, e.g., during sickness and prior to surgery.
• While the lack of adrenal sex steroids is compensated by testicular hormone synthesis in men, females may benefit from dehydroepiandrosterone treatment to prevent mood swings and depression, and to improve their health-related quality of life [12].

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 [2].

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 [9]. Recently, Norwegian researchers found young AI patients to have an increased mortality due to adrenal failure, infection, and sudden death [10]. Otherwise, AI patients have an excellent prognosis.

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 [1]. Of note, clinical symptoms may only manifest after the destruction of the vast majority of adrenal tissue [2].

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 [3]. 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 [4].

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 [5]. The annual incidence of primary AI has been stated to be <1 in 100,000 inhabitants of western Norway[6], 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 [7].

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 [8]. 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:

• Zona glomerulosa: aldosterone
• Zona fasciculata: glucocorticoids like cortisol and corticosterone
• Zona reticularis: sex steroids, e.g., dehydroepiandrosterone which is subsequently converted to androgens and estrogens
  
• Adrenal medulla: epinephrine and norepinephrine

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.

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.

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.

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.

1. Park J, Didi M, Blair J. The diagnosis and treatment of adrenal insufficiency during childhood and adolescence. Arch Dis Child. 2016; 101(9):860-865.
2. Naziat A, Grossman A. Adrenal Insufficiency. In: De Groot LJ, Beck-Peccoz P, Chrousos G, et al., eds. Endotext. South Dartmouth (MA): MDText.com, Inc.; 2000.
3. Díez López I, Rodríguez Estévez A, González Molina E, Martínez Ayucar M, Rodríguez Pérez B, Ezquieta Zubicaray B. [Virilizing congenital adrenogenital syndrome with a de novo I172N mutation: study of a new case]. An Pediatr (Barc). 2010; 72(1):72-78.
4. Talapatra I, Kalavalapalli S, Tymms DJ. Isolated hypoaldosteronism: An overlooked cause of hyponatraemia. Eur J Intern Med. 2007; 18(3):246-248.
5. Neary N, Nieman L. Adrenal insufficiency: etiology, diagnosis and treatment. Curr Opin Endocrinol Diabetes Obes. 2010; 17(3):217-223.
6. Løvås K, Husebye ES. High prevalence and increasing incidence of Addison's disease in western Norway. Clin Endocrinol (Oxf). 2002; 56(6):787-791.
7. Bornstein SR. Predisposing factors for adrenal insufficiency. N Engl J Med. 2009; 360(22):2328-2339.
8. Wallace I, Cunningham S, Lindsay J. The diagnosis and investigation of adrenal insufficiency in adults. Ann Clin Biochem. 2009; 46(Pt 5):351-367.
9. Yanase T, Tajima T, Katabami T, et al. Diagnosis and treatment of adrenal insufficiency including adrenal crisis: a Japan Endocrine Society clinical practice guideline [Opinion]. Endocr J. 2016.
10. Erichsen MM, Lovas K, Fougner KJ, et al. Normal overall mortality rate in Addison's disease, but young patients are at risk of premature death. Eur J Endocrinol. 2009; 160(2):233-237.
11. Simunkova K, Husebye ES. Adrenal Insufficiency Therapy: How to Keep the Balance between Good Quality of Life and Low Risk for Long-Term Side Effects? Front Horm Res. 2016; 46:196-210.
12. Alkatib AA, Cosma M, Elamin MB, et al. A systematic review and meta-analysis of randomized placebo-controlled trials of DHEA treatment effects on quality of life in women with adrenal insufficiency. J Clin Endocrinol Metab. 2009; 94(10):3676-3681.