Primary adrenal insufficiency
(Addison's disease)

Addison's disease is the chronic form of primary adrenal insufficiency in which damage affects the adrenal cortex and causes a progressive reduction in the production of cortisol and, in most cases, aldosterone. Unlike central forms, in which the deficiency results from reduced secretion of adrenocorticotropic hormone (ACTH) or corticotropin-releasing hormone (CRH), in Addison's disease the gland itself is the endocrine bottleneck and loses the ability to respond even to intense stimulation. Clinically, the body may appear relatively compensated under basal conditions but becomes vulnerable when cortisol requirements increase, with a risk of adrenal crisis during infections, dehydration or medical procedures.

In clinical practice, Addison's disease is relevant for three reasons: the initial symptoms are often nonspecific, diagnosis requires a coherent pathophysiological interpretation of laboratory and clinical findings, and prognosis critically depends on patient education and prevention of acute episodes. Furthermore, because autoimmunity is the most common cause in high-income countries, Addison's disease frequently occurs within autoimmune polyglandular disease, which requires longitudinal surveillance and integrated management.

The epidemiology of Addison's disease reflects the combination of its rarity and the geographic variability of its causes. In high-income settings, autoimmune adrenalitis accounts for the vast majority of cases of chronic primary adrenal insufficiency, whereas forms secondary to tuberculosis or other infiltrative disorders are more common in areas with a higher prevalence of specific infections or more limited access to healthcare. In populations of European ancestry, prevalence is often reported as approximately one case per several thousand individuals, with a higher frequency in women than in men, consistent with the distribution of autoimmune endocrine diseases.

The age at presentation varies widely, although many diagnoses are made in adulthood, when the loss of adrenocortical reserve crosses a critical threshold and symptoms become clinically evident. This epidemiological feature is important because it suggests that some patients pass through a prolonged subclinical phase: autoimmune damage may progress slowly and become apparent only when a stressful event increases cortisol demand beyond the remaining capacity. In this context, a history of recurrent episodes of collapse or unusually slow recovery after febrile illnesses may represent an individual epidemiological clue that is as useful as population prevalence data.

The principal risk factors are related to autoimmune susceptibility. A family history of autoimmune disease and a personal history of autoimmune thyroiditis, type 1 diabetes, celiac disease, vitiligo, pernicious anemia or primary ovarian insufficiency increase the pre-test probability of autoimmune adrenalitis. In patients with autoimmune polyglandular syndromes, Addison's disease may emerge as the second or third endocrine manifestation, and risk changes over time: a patient with known endocrine autoimmunity is not free from risk after only a few years, because progression may be delayed and gradual.

A further epidemiological group includes patients with non-autoimmune conditions that cause bilateral adrenal destruction, including chronic infections, metastases, lymphomas, bilateral hemorrhage and infiltrative diseases. In these cases, risk factors are related to the underlying disorder and its treatments. Although tuberculosis is less common than in the past in many regions, it remains a relevant cause in selected settings and may present with enlarged adrenal glands in the early stages and calcifications in later stages, making imaging both an epidemiological and diagnostic element.

A clinically important issue is vulnerability to adrenal crisis. Patients with known Addison's disease may develop a crisis particularly when there is no stress-management plan, when vomiting or diarrhea prevents oral medication intake, or when the initial stages of decompensation are not recognized promptly. The epidemiology of acute events is therefore closely related to treatment adherence, the quality of patient education, the availability of parenteral hydrocortisone and the ability of healthcare services to recognize and treat the endocrine emergency promptly.

Finally, several physiological conditions increase the risk of decompensation without changing disease prevalence. Pregnancy, intense heat, prolonged exercise, surgery and systemic infections increase glucocorticoid and mineralocorticoid requirements and therefore increase the probability that previously undiagnosed Addison's disease will become clinically manifest or that a patient already receiving treatment will become unstable. The epidemiology of Addison's disease is therefore inseparable from the patient's clinical and living environment and from the healthcare system's ability to support the patient during high-risk periods.

In most cases, Addison's disease results from autoimmune adrenalitis that progressively destroys the steroid-producing cells of the adrenal cortex. The most characteristic immunological target is the enzyme 21-hydroxylase, and the presence of autoantibodies directed against this enzyme is an important marker of autoimmune etiology. The pathogenic process is predominantly mediated by cellular immunity: autoreactive T lymphocytes infiltrate the adrenal gland, promote cytotoxicity and chronic inflammation and gradually reduce the functional mass capable of producing cortisol and aldosterone. Functional loss is often slow, and the patient passes through stages in which the axis increases ACTH secretion to maintain hormone production, until the compensatory capacity is exhausted.

In addition to the autoimmune form, infectious, infiltrative, vascular and neoplastic causes exist. Tuberculosis can cause bilateral necrosis and destruction; metastases and lymphomas may replace cortical tissue; bilateral hemorrhage may cause acute loss of function; and certain genetic and metabolic disorders may lead to primary insufficiency with specific clinical and laboratory features. This etiological diversity is relevant because it changes the timing of onset: rapid destruction produces acute presentations, whereas infiltrative or autoimmune processes tend to cause a subtle and cumulative onset.

The pathophysiology of Addison's disease is dominated by two functional components: cortisol deficiency and aldosterone deficiency. Cortisol deficiency impairs the maintenance of blood pressure by reducing vascular responsiveness to catecholamines and angiotensin II, decreases gluconeogenesis and energy-substrate availability, and alters modulation of the inflammatory response. These mechanisms account for fatigue, weight loss, hypoglycemia in predisposed settings, nausea and poor tolerance of stress. When present, aldosterone deficiency causes renal sodium loss, extracellular volume contraction, hypotension and increased renin, with a tendency toward hyperkalemia and occasionally mild metabolic acidosis.

A distinguishing feature of the primary form is the marked increase in ACTH caused by loss of cortisol-mediated negative feedback. ACTH is derived from the precursor pro-opiomelanocortin, which is shared with melanotropic peptides, explaining the skin and mucosal hyperpigmentation that often precedes or accompanies diagnosis. At the same time, elevated ACTH indicates that the pituitary gland is strongly stimulating the adrenal glands, but the adrenal cortex cannot respond. This is a key concept for distinguishing Addison's disease from central forms, in which ACTH is low or inappropriately normal and hyperpigmentation is absent.

Pathophysiology becomes particularly critical during stress, when cortisol requirements normally increase. A healthy individual rapidly increases cortisol production to maintain blood glucose, blood pressure and the immune response. In Addison's disease, this increase is impossible, and a febrile infection or gastroenteritis may precipitate hypotension, hypoglycemia, dehydration and electrolyte abnormalities within a few hours. Adrenal crisis is therefore not merely a more severe version of chronic disease but the pathophysiological expression of depleted adrenal reserve during a period of increased demand.

Finally, Addison's disease frequently occurs within systemic or multiple endocrine autoimmunity, which modifies the patient's overall pathophysiology. Coexisting hypothyroidism, type 1 diabetes or celiac disease may intensify fatigue and weight loss and make clinical interpretation more complex. Furthermore, correction of other hormonal deficiencies may alter metabolism and glucocorticoid requirements, which is why the pathophysiological approach must remain integrated rather than compartmentalized.

The clinical presentation of Addison's disease is often gradual and characterized by symptoms that may be mistaken for stress, depression or functional gastrointestinal disorders. The key is to recognize a pattern of progressive deterioration, reduced tolerance of stress and objective findings consistent with hypovolemia and endocrine deficiency. Interindividual variability is considerable because presentation depends on the rate of cortical destruction, the severity of mineralocorticoid deficiency and the presence of autoimmune or chronic comorbidities.

During the medical history, profound and persistent fatigue is often the dominant symptom, accompanied by muscle weakness, reduced ability to perform daily activities and slow recovery after exertion or intercurrent illnesses. Many patients report weight loss and reduced appetite, sometimes associated with recurrent nausea, vague abdominal pain and changes in bowel habits. Salt craving is a suggestive feature reflecting sodium loss in forms with aldosterone deficiency and may be described as actively seeking salt or showing a pronounced preference for salty foods.

Cardiovascular and autonomic symptoms include dizziness, blurred vision or syncope on standing, palpitations caused by compensatory tachycardia and intolerance of heat or physical exertion. These symptoms often worsen during dehydration, fever or diarrhea. A history of recurrent vomiting and collapse during gastroenteritis, with rapid improvement following intravenous fluids and empirical steroid treatment, when present, is highly informative because it suggests previously unrecognized adrenal crises or impending crises.

The physical examination should systematically assess cutaneous and hemodynamic signs. Hyperpigmentation is one of the most characteristic findings: it may be apparent in the palmar creases, elbows, areas of friction, scars and oral mucosa and should be distinguished from tanning or common pigmentary changes. Hypotension, particularly orthostatic hypotension, is frequent and is associated with signs of extracellular volume contraction. Loss of muscle mass and weight loss may be present in advanced disease. Vitiligo, signs of thyroid disease or other autoimmune stigmata strengthen the suspicion of an autoimmune etiology.

Neuropsychiatric manifestations such as irritability, apathy or impaired concentration may occur and are often secondary to hypoperfusion, electrolyte abnormalities and energy deficiency. Particularly when diagnosis is delayed, sleep quality and mood may also be impaired, and these features may be incorrectly interpreted as primary psychiatric problems. They should be considered within an endocrine framework when systemic symptoms and compatible objective findings coexist.

When the disease progresses toward acute decompensation, the clinical picture may become dramatic, with intractable vomiting, diarrhea, abdominal pain, fever, confusion and hypotension progressing to shock. At this stage, Addison's disease presents as an emergency, and treatment must precede complete diagnostic definition because reversibility depends on the rapid restoration of glucocorticoids, circulating volume and metabolic balance.

Addison's disease should be suspected when nonspecific symptoms form a coherent pattern of cortisol deficiency associated with mineralocorticoid deficiency. The combination of marked fatigue, weight loss, recurrent nausea and orthostatic hypotension is particularly suggestive, especially when the patient reports salt craving or physical examination reveals hyperpigmentation. In internal medicine, Addison's disease should be considered in patients with otherwise unexplained hyponatremia, hyperkalemia and clinical deterioration that is disproportionate during infections or dehydration.

The presence of hyperpigmentation is one of the most useful clues because it points toward a primary form. Although it is not always obvious, systematic examination of the mucous membranes and skin folds may transform a vague suspicion into a concrete diagnostic hypothesis. Similarly, a personal or family history of endocrine autoimmunity should lower the threshold for suspicion: in a patient with autoimmune thyroiditis or type 1 diabetes, progressive fatigue and hypotension should not automatically be attributed to stress or physical deconditioning.

Suspicion should be high in the emergency department when a patient presents with vomiting, abdominal pain and hypotension, particularly when these findings are associated with hyponatremia and hyperkalemia. These presentations may mimic sepsis or acute abdominal disease, but compatible electrolyte abnormalities and cutaneous signs may provide rapid diagnostic orientation. In these circumstances, the clinical priority is to initiate urgent treatment and obtain samples for cortisol and ACTH before glucocorticoid administration, without delaying treatment when the patient is hemodynamically unstable.

In the outpatient setting, suspicion should also arise in the presence of apparently minor but persistent symptoms, including unintentional weight loss, worsening fatigue, chronic hypotension, salt craving, subtle hyperpigmentation and recurrent episodes of post-infectious malaise. Recognition at this stage is particularly important because it can prevent the first adrenal crisis, which is often the event leading to diagnosis in previously unrecognized disease.

Finally, the temporal dimension should be considered: Addison's disease may become clinically evident after a stressful event because cortical reserve was already nearly exhausted. In a patient who appeared compensated until recently, gastroenteritis or pneumonia may reveal advanced adrenal insufficiency. Hemodynamic instability during an infection should therefore not be interpreted solely as a marker of infection severity but also as a possible endocrine inability to sustain the physiological stress response.

Diagnosis of Addison's disease requires confirmation of cortisol deficiency and demonstration that the defect is primary, distinguishing it from central forms and from other conditions that alter serum sodium and blood pressure. Whenever possible, the first step is to measure morning cortisol together with ACTH, sodium, potassium, blood glucose and renal function. A clearly low morning cortisol concentration in a symptomatic patient strengthens the suspicion, but confirmation often requires a dynamic test assessing the adrenal response to stimulation.

The most widely used test for confirming primary adrenal insufficiency is stimulation with synthetic ACTH, which assesses the increase in cortisol after a standardized stimulus. In Addison's disease, the adrenal gland cannot produce an adequate response because the steroidogenic cell mass is reduced or nonfunctional. Basal ACTH is typically elevated, consistently with the loss of negative feedback. In the presence of hemodynamic instability or suspected adrenal crisis, blood samples for cortisol and ACTH should be obtained before hydrocortisone is administered whenever possible, but treatment must take priority when the patient is clinically compromised.

Diagnostic assessment of Addison's disease

• Confirmation of adrenal insufficiency using morning cortisol and an ACTH stimulation test when the clinical condition permits.
• Demonstration of a primary form through elevated ACTH and a compatible electrolyte assessment, including sodium and potassium, together with evaluation of hemodynamic impairment.
• Etiological assessment using anti-21-hydroxylase antibodies and evaluation of mineralocorticoid deficiency through renin and aldosterone measurements to guide replacement therapy.
• Targeted investigation when autoimmunity cannot be documented, including adrenal imaging and selected tests for alternative causes based on sex, age and clinical context.

Etiological definition is an integral part of clinical diagnosis because it determines follow-up and surveillance. When anti-21-hydroxylase antibodies are positive, an autoimmune etiology is highly probable, and screening or monitoring for other autoimmune endocrinopathies is appropriate. When antibodies are negative or the clinical context suggests alternative causes, appropriate adrenal imaging may identify hemorrhage, infiltrative lesions or bilateral masses, while the clinical history may point toward tuberculosis or malignancy. In males, particularly when presentation is atypical or diagnosis occurs at a relatively young age, selected genetic or metabolic causes should be considered and investigated because treatment of the hormonal deficiency represents only one component of overall management.

The differential diagnosis includes conditions that mimic fatigue and hypotension, but the combined pattern of hyperpigmentation, electrolyte abnormalities, elevated ACTH and an inadequate response to ACTH stimulation strongly supports Addison's disease. It is also essential to distinguish chronic Addison's disease from an ongoing adrenal crisis: during a crisis, immediate treatment and stabilization are the priorities, whereas the complete diagnostic work-up continues once clinical safety has been restored. This approach reduces the risk of delay and permits rapid initiation of appropriate replacement therapy and preventive measures for future episodes.

Finally, diagnosis should include an assessment of severity and the risk of decompensation. Marked hypotension, dehydration, hypoglycemia or significant electrolyte abnormalities indicate the need for more intensive management and immediate operational instructions. This step is part of the diagnostic reasoning because, in Addison's disease, diagnosis is incomplete unless it results in a safety plan for stress and emergency situations.

The classification of Addison's disease is based on its nature as primary adrenal insufficiency, but this category includes clinical forms with different implications. A first distinction is between autoimmune and non-autoimmune Addison's disease. The autoimmune form is frequently associated with anti-21-hydroxylase antibodies and with the risk of concurrent or future endocrinopathies, whereas non-autoimmune forms require etiological investigation for infections, infiltrative diseases or vascular events and have a prognosis that also depends on the underlying disorder.

A second distinction concerns the degree of mineralocorticoid impairment. Many patients have significant aldosterone deficiency, with hyponatremia, hyperkalemia and extracellular volume contraction, whereas mineralocorticoid deficiency may be less evident during the early stages or in certain subtypes. This variability influences the clinical presentation and the strategy for fludrocortisone and salt replacement. The patient's day-to-day clinical severity is often more closely related to hemodynamic stability and volume control than to the nonspecific symptoms of cortisol deficiency.

From a temporal perspective, it is useful to distinguish forms with an insidious onset from those that become manifest acutely. In most autoimmune cases, progression is slow and diagnosis follows several months of symptoms, whereas some vascular or infectious causes can produce rapid functional loss. Another clinically important category consists of patients in a nearly compensated phase who develop a crisis as the first manifestation: in these cases, severity had not previously been recognized, and classification should account for the fact that adrenal reserve has already become critically depleted.

The category of greatest severity is adrenal crisis, a condition of acute insufficiency with hemodynamic instability and a risk of shock. Between chronic stability and established crisis, however, there is an intermediate stage of impending crisis or imminent decompensation, in which vomiting, fever and diarrhea prevent oral medication intake and require parenteral treatment before shock develops. Recognizing and treating this phase promptly is an operational aspect of classification that directly affects individual prognosis.

Finally, classification should consider the context of autoimmune polyglandular disease. A patient with Addison's disease occurring within a polyglandular syndrome requires an integrated assessment of risk because the appearance or treatment of other endocrinopathies may modify metabolic requirements and the risk of decompensation. Severity is therefore not determined solely by hormone concentrations but also by clinical complexity and vulnerability to predictable stressors.

Treatment of Addison's disease is based on replacement of glucocorticoids and, when required, mineralocorticoids, with the aim of restoring clinical stability under basal conditions and ensuring an adequate response to stress. Treatment is not merely a drug regimen because patient safety depends on the ability to increase the dose promptly during fever, infections, surgery or vomiting and on the availability of parenteral hydrocortisone when oral absorption is impaired. Effective management markedly reduces the risk of adrenal crisis and improves quality of life and long-term prognosis.

Basal glucocorticoid replacement is commonly provided with hydrocortisone in divided doses, with a larger dose in the morning and smaller doses later in the day to approximate the physiological circadian rhythm in a pragmatic manner. In selected subgroups, alternative regimens using low-dose prednisolone or modified-release formulations may be considered to reduce fluctuations and improve certain metabolic or quality-of-life outcomes. Dose titration is based on clinical parameters such as energy levels, body weight, blood pressure, orthostatic symptoms, sleep quality and absence of signs of glucocorticoid excess because no single reliable laboratory marker is available to guide the dose.

Mineralocorticoid replacement with fludrocortisone is an integral component of treatment in most patients with Addison's disease because aldosterone deficiency causes hemodynamic and electrolyte instability. The dose is adjusted according to blood pressure, orthostatic symptoms, sodium, potassium and markers of the renin-angiotensin system. Salt intake should also be adapted to the clinical context, with particular attention during intense heat, prolonged physical activity, diarrhea or marked sweating, when sodium loss increases and extracellular volume contraction may precipitate decompensation.

Prevention of adrenal crisis requires a structured stress-management plan. During fever or infection, the glucocorticoid dose must be increased according to clear rules that have already been discussed with the patient. In the event of vomiting or diarrhea, oral treatment may become ineffective and should be replaced by parenteral hydrocortisone, with urgent access to medical care and fluid replacement. Patient education includes early recognition of decompensation symptoms, possession of and ability to use an emergency injection kit, and medical identification that allows the condition to be recognized immediately outside specialist settings.

In selected patients, replacement with dehydroepiandrosterone (DHEA) may be considered for persistent impairment of quality of life, libido or psychophysical well-being, particularly in women, with careful monitoring and reassessment of clinical benefit. This intervention is not universally indicated and does not replace glucocorticoid and mineralocorticoid therapy, but it may represent an additional option within a genuinely individualized approach.

Management of Addison's disease also includes attention to autoimmune comorbidities, appropriate vaccinations, osteoporosis management when indicated and adaptation of treatment during pregnancy, surgery and medical procedures. During pregnancy, for example, dose adjustments and a specific plan for labor and delivery may be required because physiological stress demands adequate glucocorticoid coverage. In the perioperative setting, coverage should be planned according to the invasiveness of the procedure and the patient's clinical condition to prevent hypotension and metabolic complications.

Overall, treatment of Addison's disease is effective when it combines pharmacological therapy, education and organization. Appropriate replacement therapy restores stability, but the principal prognostic benefit derives from preventing and treating episodes of decompensation promptly because adrenal crisis is the event most directly responsible for avoidable morbidity and mortality.

Follow-up of Addison's disease has both clinical and safety objectives. In stable conditions, monitoring aims to maintain adequate replacement while avoiding glucocorticoid overexposure and to ensure hemodynamic and electrolyte control through optimization of mineralocorticoid therapy. Because there is no single biomarker for titrating hydrocortisone, assessment should be clinical and structured, including blood pressure, body weight, symptoms, sleep quality, exercise tolerance and signs of excess such as weight gain, edema, hypertension and skin fragility.

The mineralocorticoid component requires periodic measurement of sodium and potassium and a coherent assessment of blood pressure, orthostatic symptoms and fluid and sodium balance. A patient receiving insufficient fludrocortisone tends to develop hypotension, fatigue and salt craving, whereas excessive replacement may promote hypertension and hypokalemia. Assessment of renin-angiotensin system markers may help refine the dose in selected circumstances, particularly when clinical signs are ambiguous or comorbidities affect blood pressure and extracellular volume.

A central element of follow-up is the periodic verification of the patient's ability to manage stress. Dose-increase rules should be reviewed and translated into practical examples because most crises occur during predictable events such as gastroenteritis or fever. The availability and appropriate storage of a parenteral hydrocortisone kit, medical identification and adequate caregiver education are practical aspects that should be assessed as an integral part of each follow-up visit.

Follow-up should also include screening and surveillance for autoimmune comorbidities. In autoimmune Addison's disease, the possibility of developing other endocrinopathies over time justifies selective monitoring of thyroid function, blood glucose and other parameters according to the patient's profile and symptoms. Diagnosis and treatment of a new endocrinopathy may alter hormone requirements and symptom perception, and management should remain integrated to prevent treatment changes in one endocrine axis from destabilizing another.

Finally, follow-up should assess quality of life and treatment-related complications. Even when disease control is satisfactory, some patients report residual fatigue, anxiety related to the risk of adrenal crisis or difficulty managing physical activity and travel. Reviewing the dosing schedule, considering modified-release formulations when appropriate and addressing factors such as sleep and nutrition may improve well-being without increasing the risk of overtreatment. The quality of follow-up is measured not only by normal electrolyte concentrations but also by fewer emergency visits and greater stability in real-life settings.

The prognosis of Addison's disease is generally favorable when diagnosis is timely, replacement therapy is appropriate and the patient is educated to manage stress. Hormone replacement enables an active and stable life, but the condition remains associated with a risk of acute events because the physiological response to stress cannot be reproduced perfectly. Prognosis therefore depends on achieving a balance between adequate replacement and prevention of overtreatment and, above all, on avoiding delays in treating episodes of decompensation.

The most important complication is adrenal crisis, which may present with hypotension progressing to shock, dehydration, hypoglycemia and electrolyte abnormalities and is frequently precipitated by infections, vomiting, diarrhea or surgery without adequate glucocorticoid coverage. Adrenal crisis is preventable in most cases but remains a genuine risk when clear operational rules are lacking, when the patient has no access to parenteral hydrocortisone or when healthcare professionals do not recognize the diagnosis promptly. Recurrent episodes of impending crisis, although less severe, also have a substantial impact because they lead to hospital admissions, impaired quality of life and reduced patient confidence in daily disease management.

Chronic complications may result from suboptimal replacement therapy. Under-replacement promotes fatigue, hypotension and vulnerability to stress, whereas even modest but prolonged over-replacement may contribute to hypertension, weight gain, metabolic abnormalities and reduced bone mineral density. Active follow-up is therefore necessary, with periodic reassessment and dose adjustment according to changes in weight, age, lifestyle and comorbidities.

In autoimmune disease, the development of other endocrinopathies is an important prognostic consideration. Hypothyroidism, type 1 diabetes and other autoimmune disorders may increase clinical complexity and the risk of decompensation when they remain unrecognized. Furthermore, treatment changes involving other endocrine axes should be managed cautiously in patients with Addison's disease because they may alter metabolic requirements and the risk of instability. The best prognosis is achieved through integrated and longitudinally organized care.

Quality of life and psychophysical well-being are often underestimated. Even with adequate treatment, some patients continue to perceive reduced energy or greater susceptibility to fatigue, which may result from fluctuations in replacement therapy, autoimmune comorbidities or psychosocial factors. Prognostic assessment should include these aspects because they influence treatment adherence and the ability to apply stress-dosing rules correctly, which is the principal determinant of safety.

Overall, Addison's disease is a manageable condition with favorable outcomes when care is well structured. Prognosis is optimal when the patient has appropriate replacement therapy, practical skills for managing stress and access to a healthcare system capable of recognizing and treating acute episodes promptly. In the absence of these elements, the disease may become a multiplier of systemic risk, not because of biological inevitability but because of organizational and management vulnerability.