Secondary and tertiary adrenal insufficiency
(ACTH and CRH deficiency)

Secondary and tertiary adrenal insufficiency are forms of cortisol deficiency caused by reduced stimulation of the adrenal cortex along the hypothalamic-pituitary-adrenal axis. In the secondary form, the disorder originates in the pituitary gland and results in reduced secretion of adrenocorticotropic hormone (ACTH), whereas in the tertiary form the reduction in stimulation is hypothalamic, typically because of corticotropin-releasing hormone (CRH) deficiency or functional suppression of the regulatory centers. From a clinical perspective, both conditions share many manifestations of hypocortisolism, but they differ substantially from primary adrenal insufficiency because aldosterone production is generally preserved, as it is regulated mainly by the renin-angiotensin system and potassium.

The distinction between secondary and tertiary adrenal insufficiency is particularly important for understanding the causes, clinical course and likelihood of recovery of the axis. In many practical settings, the two conditions are managed according to similar principles, but the clinical history and endocrine assessment guide identification of the site of the defect, evaluation of other pituitary deficiencies and the strategy for discontinuing or modifying treatments that may have caused functional suppression. When a pituitary disorder is suspected, interpretation should be integrated with the typical presentation of ACTH deficiency, whereas in hypothalamic conditions or central suppression the framework of CRH deficiency may be useful.

The epidemiology of secondary and tertiary adrenal insufficiency is strongly influenced by the prevalence of pituitary and hypothalamic disorders and by exposure to treatments capable of suppressing the axis. Unlike primary adrenal insufficiency, which remains rare, treatment-related central forms are relatively common in clinical practice because systemic glucocorticoids, high-dose inhaled preparations, repeated intra-articular injections or extensive topical treatment may suppress ACTH secretion and cause functional adrenal atrophy. In these cases, adrenal insufficiency is often classified as glucocorticoid-induced and is physiopathologically located within the tertiary category or within integrated central suppression, with variable recovery over time.

In true secondary forms, epidemiology reflects that of pituitary diseases. Pituitary adenomas, sellar surgery, radiotherapy, pituitary apoplexy, infiltrative disorders, hypophysitis and iatrogenic or traumatic injury may reduce ACTH secretion. In these patients, the likelihood of adrenal insufficiency increases when signs of hypopituitarism coexist, when a sellar mass compresses the normal pituitary tissue or when multiple hormone deficiencies are present. The age at presentation depends on the natural history of the pituitary disorder, with peaks associated with the diagnosis of pituitary tumors and post-treatment complications.

Organic hypothalamic tertiary forms are less common overall, but become relevant in selected settings such as hypothalamic lesions, infiltrative disorders, postoperative or post-radiotherapy damage and inflammatory diseases of the central nervous system. In clinical practice, however, functional tertiary adrenal insufficiency caused by suppression of the axis accounts for the greatest epidemiological burden because the axis may remain inhibited even after glucocorticoid withdrawal and clinical vulnerability often becomes apparent during dose reduction or discontinuation.

The main risk factors for central adrenal insufficiency include the duration and cumulative dose of glucocorticoid treatment, route of administration, clinical frailty, chronic inflammatory comorbidities and factors that increase systemic exposure. Concomitant use of treatments that reduce ACTH secretion, including some opioids, is another relevant epidemiological factor in populations affected by chronic pain. At the same time, signs of sellar disease, recent-onset headache, visual disturbances or amenorrhea in a person with fatigue and hypotension should lower the threshold for suspecting secondary adrenal insufficiency.

Adrenal crisis is a critical epidemiological concern. Although mineralocorticoid deficiency is generally absent, adrenal crisis may occur in both central forms when acute illness rapidly increases cortisol requirements or when oral absorption is impaired. The risk is particularly relevant during glucocorticoid tapering, in the first weeks after pituitary surgery, following infections accompanied by high fever and in any setting involving vomiting or diarrhea. The epidemiology of acute events therefore depends on the quality of preventive measures and the clarity of stress-management instructions.

Finally, the true epidemiological impact is often underestimated because many forms are oligosymptomatic and are identified only through targeted testing. This is particularly true of treatment-induced axis suppression, in which the patient may appear stable until exposed to significant physiological stress. Risk assessment and test selection should therefore be based not only on the presence of symptoms but also on the pharmacological history and recent clinical trajectory.

Secondary and tertiary adrenal insufficiency share the same final consequence, namely reduced stimulation of the adrenal cortex and insufficient production of cortisol, but differ in the site of the defect and in certain dynamic aspects of regulation. Under physiological conditions, the hypothalamus releases CRH and vasopressin, which stimulate the pituitary gland to produce ACTH. ACTH maintains both cortisol secretion and the trophic integrity of the zona fasciculata and zona reticularis. Cortisol, in turn, exerts negative feedback at several levels, stabilizing axis output and modulating the magnitude of responses to physiological stress.

In secondary adrenal insufficiency, the disorder is pituitary in origin. ACTH is low or inappropriately normal in relation to the cortisol concentration and, over time, the lack of stimulation causes a functional reduction in the adrenal response. Because the zona glomerulosa is less dependent on ACTH and more dependent on the renin-angiotensin system, aldosterone secretion is generally preserved. This explains why hyperkalemia and marked salt craving are less typical than in primary adrenal insufficiency, whereas hyponatremia may still occur because reduced cortisol impairs water balance and increases secretion of antidiuretic hormone (ADH), producing a clinical profile that may resemble euvolemic hyponatremia.

In tertiary adrenal insufficiency, the defect involves the hypothalamus or its functional regulation. The most common form is suppression of the axis by exogenous glucocorticoids. Glucocorticoid exposure reduces CRH and ACTH secretion through negative feedback, causes central hypofunction and, over time, produces adrenal atrophy of the zona fasciculata. Recovery is not immediate after dose reduction or discontinuation because restoration of CRH and ACTH secretion may be slow and adaptation of the adrenal gland requires time. This creates a clinical window during which the patient remains vulnerable to physiological stress even in the absence of significant symptoms at rest.

From a pathophysiological perspective, manifestations result mainly from glucocorticoid deficiency. Cortisol is essential for maintaining vascular tone and the pressor response to catecholamines, ensuring glucose availability through gluconeogenesis and modulating inflammation. Deficiency causes fatigue, reduced tolerance to stress, a tendency toward hypotension, nausea and weight loss. The absence of hyperpigmentation is a key feature of central forms because ACTH is not elevated as it is in primary adrenal insufficiency, and there is therefore no increase in proopiomelanocortin-derived peptides.

Differences between secondary and tertiary adrenal insufficiency become evident when interpreting the clinical history and the potential for recovery of the axis. A structural pituitary lesion may cause persistent deficiency and may be associated with other pituitary hormone deficiencies. Treatment-induced tertiary suppression may be reversible, but recovery times are variable and cannot be predicted solely from the administered dose because cumulative exposure and individual axis sensitivity influence the duration of suppression. Pathophysiology therefore includes a central concept, namely axis reserve, which may be adequate under basal conditions but insufficient when physiological demand increases.

Finally, pathophysiology interacts with concomitant disorders. Pituitary disease may coexist with central hypothyroidism, gonadotropin deficiency or growth hormone deficiency, and each of these disorders affects energy, body composition and well-being, making interpretation of the clinical picture more complex. In glucocorticoid-induced forms, inflammatory comorbidities, muscle frailty and metabolic disturbances may mask or mimic symptoms of hypocortisolism. Pathophysiology must therefore always be translated into integrated reasoning that combines clinical context, signs and dynamic testing.

The clinical manifestations of secondary and tertiary adrenal insufficiency predominantly reflect cortisol deficiency and tend to involve fewer electrolyte abnormalities than primary adrenal insufficiency. Onset may be insidious, with nonspecific symptoms persisting for weeks or months, or the condition may emerge abruptly during a stressful event. Variability is influenced by the rate at which ACTH secretion declines, the degree of adrenal atrophy and the presence of other pituitary dysfunctions or concomitant treatments.

During history taking, fatigue is often the most consistent symptom and may be associated with reduced exercise tolerance, weakness and slow recovery after infections. Nausea, loss of appetite, weight loss and vague muscular or joint pain may occur. The tendency toward hypoglycemia is more evident in children, frail older adults and people receiving treatment for diabetes, but it may also occur in adults with reduced metabolic reserve. In many settings, particularly in tertiary forms associated with glucocorticoid withdrawal, patients report marked deterioration during dose reduction or in the days following discontinuation. This temporal pattern represents an important clinical clue.

The physical examination may reveal hypotension, which is often less pronounced than in Addison disease but may still be clinically significant, particularly on standing or in the presence of dehydration. Hyperpigmentation is typically absent and, when correctly interpreted, this finding supports a central form. Signs of pituitary disease may coexist and include reduced muscle mass, trophic changes, reduced libido, amenorrhea or other indicators of hypopituitarism. In the setting of a sellar mass or recent pituitary treatment, these findings carry considerable diagnostic weight.

From an electrolyte perspective, hyponatremia may occur, particularly during acute illness, because of a combination of impaired suppression of ADH and reduced effective filtration during physiological stress and disease. Hyperkalemia is generally absent because aldosterone secretion is preserved, and this distinction is one of the principal clinical features separating central from primary adrenal insufficiency. However, normal potassium levels must not reduce the urgency of management in an unstable patient because shock caused by cortisol deficiency may occur even when electrolyte concentrations remain relatively stable.

In acute presentations, symptoms may include vomiting, abdominal pain, fever, confusion and significant hypotension. Distinguishing adrenal crisis from other medical emergencies may be difficult, but a history of steroid therapy, a pituitary clinical context and the absence of findings typical of Addison disease may provide guidance. Clinical management requires immediate treatment of suspected hypocortisolism when the probability is substantial because the response to hydrocortisone and intravenous fluids is often rapid and may be lifesaving.

Finally, in forms associated with hypothalamic-pituitary disease, the clinical presentation is not limited to cortisol deficiency. Symptoms of central hypothyroidism, hypogonadism or other deficiencies may amplify fatigue and reduced performance. In these patients, the clinical picture is often a mosaic and evaluation must reconstruct the temporal sequence, distinguishing manifestations predominantly caused by hypocortisolism from those resulting from impairment of other hormonal axes.

Secondary or tertiary adrenal insufficiency should be suspected when symptoms of hypocortisolism occur in a compatible clinical context. A history of glucocorticoid treatment, including nonsystemic treatment, is one of the most important warning signs. Recent dose reduction, discontinuation after prolonged use or the development of fatigue and hypotension during infection suggest possible suppression of the axis. Suspicion is particularly relevant in these settings because the patient may not appear severely ill until exposed to significant physiological stress.

Suspicion should also remain high in the presence of known or possible pituitary or hypothalamic disease. Recent-onset headache, visual disturbances, a history of sellar surgery or radiotherapy, signs of hypopituitarism and unexplained hyponatremia support secondary adrenal insufficiency. In a patient with features compatible with ACTH deficiency, assessment of cortisol secretion and the axis becomes a clinical priority because inadequate glucocorticoid coverage increases the risk of instability during intercurrent events.

In hospital settings, adrenal insufficiency should be considered when a patient develops hypotension or vasopressor requirements that are disproportionate to the apparent clinical condition, particularly in the presence of a history of steroid exposure or sellar disease. Vomiting, diarrhea, fever and impaired consciousness in a patient who has discontinued glucocorticoids or uses them intermittently are high-risk situations. In the emergency department, the combination of hyponatremia, hypoglycemia and hypotension in a patient with relevant risk factors should prompt immediate treatment in addition to diagnostic assessment.

In organic hypothalamic tertiary forms, suspicion is supported by evidence of global hypothalamic dysfunction and a context compatible with CRH deficiency, in which reduced central stimulation may involve several hormonal axes and regulatory functions. Even in these settings, however, clinical reasoning should maintain a pragmatic priority: rapidly identifying the risk of cortisol deficiency and preventing acute deterioration.

Finally, suspicion should be maintained when symptoms persist without an alternative explanation and when the clinical trajectory is consistent with reduced stress reserve. A patient who reports marked relapses after infections, difficulty recovering energy after steroid dose reduction or recurrent episodes of malaise associated with hypotension should undergo assessment of the axis even when findings are subtle. In these forms, the greatest clinical benefit derives from preventing adrenal crisis through reasoned diagnosis and clearly established stress-management rules.

The diagnosis of secondary and tertiary adrenal insufficiency requires confirmation of cortisol deficiency and demonstration that the defect is central, integrating basal and dynamic tests with the clinical history. The initial assessment often includes morning cortisol together with ACTH, serum sodium, blood glucose and, when useful, dehydroepiandrosterone sulfate (DHEA-S). In central forms, ACTH tends to be low or inappropriately normal and DHEA-S may be reduced, consistently with diminished stimulation of the zona reticularis. However, a single basal measurement may be insufficient because cortisol concentrations are variable and are influenced by physiological stress, acute illness and analytical interference.

When values are intermediate or clinical suspicion is substantial, confirmation is obtained through dynamic tests that assess the ability of the adrenal glands to respond to stimulation. Stimulation with synthetic ACTH is widely used, but interpretation must consider that in the early stages of central deficiency the adrenal gland may still produce a preserved response because atrophy is not yet complete. In these settings, tests that assess the integrity of the central axis may be required in specialist practice, with selection guided by the clinical context, risk profile and local availability.

Diagnostic assessment of central adrenal insufficiency

• Basal assessment with morning cortisol and ACTH, integrated with serum sodium, blood glucose and markers of the adrenal androgen axis when useful.
• Confirmation with a dynamic test of adrenal reserve, selecting the most appropriate method according to pretest probability and the timing of the deficiency.
• Identification of the site of the defect through pathophysiological interpretation and concomitant assessment of other pituitary axes, with sellar or hypothalamic imaging when indicated.
• Reconstruction of treatment-related risk by evaluating the type, dose and duration of glucocorticoid exposure and establishing a pathway for tapering and reassessment of the axis according to shared recommendations.

The differentiation between secondary and tertiary adrenal insufficiency is often based on the clinical history and evidence of pituitary or hypothalamic disease. In a patient with a sellar lesion or after pituitary surgery, the likelihood of ACTH deficiency is high and the diagnostic assessment should include prolactin, thyroid-stimulating hormone (TSH) and thyroid hormones, gonadotropins and other markers of hypopituitarism. In glucocorticoid-induced tertiary forms, the pharmacological history is decisive and testing must answer a practical question: whether the axis has recovered sufficiently to withstand physiological stress and whether it is safe to continue dose reduction.

In acute conditions or in the emergency department, diagnostic investigations must not delay treatment when the patient is unstable. Blood samples for cortisol and ACTH should be obtained before hydrocortisone administration when possible, but correction of glucocorticoid deficiency and fluid replacement take priority in patients with hypotension or confusion. After stabilization, the diagnostic work-up can be completed with dynamic testing and structural identification of the underlying cause.

The differential diagnosis includes hyponatremia from other causes, sepsis, heart failure, liver failure, hypothyroidism and acute gastrointestinal disorders. The key feature is that central forms tend to show non-elevated ACTH, absence of hyperkalemia and absence of hyperpigmentation, whereas a history of steroid therapy or pituitary disease provides decisive guidance. Diagnosis is complete only when it leads to a safety plan for physiological stress because the primary clinical objective is to prevent rapid deterioration during acute illness.

The classification of central adrenal insufficiency should be clinically useful. The first distinction separates secondary adrenal insufficiency caused by pituitary disease from tertiary adrenal insufficiency of hypothalamic origin or caused by central suppression. This distinction is relevant because secondary adrenal insufficiency is often associated with multiple deficiencies and the need for neuroradiological assessment, whereas glucocorticoid-induced tertiary adrenal insufficiency is often potentially reversible but requires variable recovery times and a cautious tapering protocol.

A second distinction concerns timing. It is useful to separate recent forms from chronic forms with established adrenal atrophy. In recent forms, particularly after pituitary surgery or during the early phase of glucocorticoid-induced suppression, the response to dynamic testing may remain partially preserved, whereas in chronic forms reserve is more clearly reduced. This distinction affects test selection and the intensity of stress dosing while awaiting definitive assessment.

From a clinical perspective, low-impact forms characterized by mild symptoms and hemodynamic stability can be distinguished from high-risk forms in which the patient has significant hypotension, marked hyponatremia, hypoglycemia or comorbidities that increase vulnerability. In these situations, even moderate cortisol deficiency may become clinically dangerous because the body lacks adequate compensatory reserve.

The most severe category is adrenal crisis, which may also occur in central forms. Between clinical stability and established crisis, there is an intermediate phase of impending decompensation that is particularly common when the patient has vomiting or diarrhea and cannot take oral treatment. At this stage, practical classification must recognize the risk and prompt early parenteral management because progression may be rapid.

Finally, glucocorticoid-induced tertiary forms may also be classified according to the probability of recovery, which depends on cumulative dose, duration of treatment and individual axis vulnerability. This classification is not merely theoretical because it determines the duration of follow-up and the need for prolonged safety instructions even after apparent discontinuation, particularly in patients with high or repeated exposure.

Treatment of secondary and tertiary adrenal insufficiency is centered on glucocorticoid replacement and prevention of decompensation during physiological stress. Because aldosterone secretion is generally preserved, mineralocorticoid replacement is not routinely required, and this is one of the practical features distinguishing central from primary adrenal insufficiency. The aim is to restore sufficient glucocorticoid exposure to ensure daily stability and an adequate response to infection, surgery, trauma or gastrointestinal illness.

Basal replacement is often provided with hydrocortisone in divided doses, with a larger dose in the morning and smaller doses later in the day, adjusted according to clinical parameters. In selected settings, low-dose regimens using longer-acting glucocorticoids may be considered, with careful avoidance of overtreatment and maintenance of the lowest effective dose. Dose titration is based on energy levels, body weight, blood pressure, sleep quality, absence of nausea and the ability to perform daily activities, while avoiding signs of glucocorticoid excess such as weight gain, edema and skin fragility.

A central component of treatment is stress dosing. During fever or infection, the dose should be increased according to clear instructions previously discussed with the patient. If vomiting or diarrhea prevents oral administration, treatment must be changed to parenteral hydrocortisone together with fluid replacement. These rules are particularly important in glucocorticoid-induced tertiary adrenal insufficiency because the patient may feel relatively well until an acute event occurs, and adrenal crisis may be the first clinically recognizable manifestation of axis suppression.

In secondary forms associated with pituitary disease, treatment must be integrated into the overall management of hypopituitarism. The sequence of replacement is essential when other deficiencies coexist because correction of thyroid hormone deficiency or introduction of other treatments may modify metabolism and glucocorticoid requirements. In these patients, specialist assessment of the complete hormonal profile and management of the underlying cause, including surgery, radiotherapy or treatment of the mass, are integral components of endocrine treatment.

In tertiary forms, the principal therapeutic component is often gradual dose reduction, with reassessment of axis reserve and maintenance of adequate coverage during periods of risk. The rationale is to allow progressive recovery of CRH and ACTH secretion and restoration of adrenal function while minimizing the risk of decompensation. Suppression may persist for a prolonged period and requires follow-up that extends beyond simple discontinuation of treatment.

In emergencies or in the presence of hemodynamic instability, treatment must be immediate. Administration of high-dose hydrocortisone and correction of intravascular volume take priority and must not be delayed by complex testing. After stabilization, the diagnostic and therapeutic strategy can be recalibrated according to the underlying cause and the likelihood of recovery, with a preventive plan designed to reduce recurrence.

Follow-up of central adrenal insufficiency aims to maintain adequate replacement, prevent episodes of decompensation and assess recovery of the axis when possible. In structural secondary forms, follow-up includes surveillance of the pituitary disorder and other hormonal axes because clinical stability depends on integrated management of hypopituitarism. In glucocorticoid-induced tertiary forms, follow-up is often focused on the withdrawal pathway and assessment of axis reserve, with recovery times that may be prolonged and highly variable.

Clinical monitoring of glucocorticoid replacement is based on well-being, blood pressure, body weight, gastrointestinal symptoms and functional capacity. Findings suggesting underreplacement include persistent fatigue, nausea and hypotension, whereas signs of overreplacement include weight gain, edema, insomnia and deterioration of the metabolic profile. Because laboratory markers are not reliable for titrating the daily replacement dose, clinical review must accurately reconstruct the course of symptoms and recent exposure to physiological stress.

A cornerstone of follow-up is periodic verification of stress-dosing rules and the availability of parenteral hydrocortisone for emergencies. Reduction in emergency admissions depends more on these practical measures than on perfect basal laboratory values. The presence of a medical identification document that makes the condition immediately recognizable and education of caregivers are safety measures that should be reassessed over time, particularly in older patients or those with comorbidities.

In tertiary forms, reassessment of the axis requires a defined strategy. After glucocorticoid dose reduction or discontinuation, basal and dynamic tests are used to determine whether the response is adequate, with cautious interpretation because recovery may be gradual. During this phase, maintaining stress-dosing instructions is essential even when symptoms improve because reserve may still be insufficient during acute illness. Management should be particularly careful in patients with prolonged or repeated exposure and in those who have undergone procedures or have chronic inflammatory conditions that make future steroid use likely.

Finally, in secondary forms, surveillance should include neuroradiological assessment when indicated and monitoring of the outcomes of pituitary treatment. ACTH deficiency often coexists with other deficiencies and stability requires coordinated adjustments. Follow-up is effective when it ensures continuity of care, reduces the incidence of adrenal crisis and enables the patient to manage predictable events such as infections and procedures safely.

The prognosis of secondary and tertiary adrenal insufficiency is generally favorable when the condition is recognized and treated with adequate replacement and a clear stress-management plan. However, prognosis depends critically on prevention of acute complications because the inability of the adrenal cortex to respond to physiological stress can rapidly precipitate hemodynamic instability and metabolic abnormalities. In glucocorticoid-induced tertiary adrenal insufficiency, prognosis also includes the likelihood of recovery of the axis, which may be complete but cannot be predicted precisely for an individual patient and therefore requires follow-up.

The most important complication is adrenal crisis, which may occur even in the absence of aldosterone deficiency. The main precipitating factors are infection, gastroenteritis with vomiting or diarrhea, surgery without adequate glucocorticoid coverage and inappropriate discontinuation of glucocorticoids. Hyponatremia and hypoglycemia may contribute to confusion and clinical deterioration. Adrenal crisis is often preventable through education, access to parenteral treatment and early recognition, and prognosis improves substantially when these measures are consistently integrated into care.

Other complications arise from suboptimal replacement. Underreplacement promotes recurrent episodes of malaise and vulnerability to physiological stress, whereas even mild but chronic overreplacement may increase metabolic and cardiovascular risk and contribute to osteopenia. The best prognosis therefore requires careful balance, periodic reassessment and dose adjustment over time, avoiding both an excessively conservative approach that leaves the patient symptomatic and excessive treatment that exposes the patient to glucocorticoid-related adverse effects.

In secondary forms, prognosis is also influenced by the underlying pituitary disorder. Tumors, the consequences of radiotherapy and hypophysitis may cause multiple hormone deficiencies and require prolonged, integrated monitoring. In these patients, complications may result not only from cortisol deficiency but also from the combination of other deficiencies that amplify fatigue and frailty. Management of replacement therapies involving other hormonal axes must also be coordinated because changes in metabolism may alter glucocorticoid requirements.

In tertiary forms, a relevant prognostic risk is recurrence of suppression following new courses of steroids or exacerbations of the underlying disease. Even when the axis appears to have recovered, renewed exposure may reactivate vulnerability. The most favorable prognosis is achieved when the pharmacological history is clearly documented, tapering is managed in a structured manner and the patient has the practical skills required to manage fever, medical procedures and gastrointestinal illness.

Overall, secondary and tertiary adrenal insufficiency are manageable conditions with a high probability of a favorable outcome, but they require preventive care focused on safety. The most important prognostic difference does not depend on the numerical cortisol value obtained from a single blood sample, but on the ability to recognize the condition, adapt treatment to predictable physiological stress and ensure continuity of care over time.