Pituitary adrenocorticotropic hormone (ACTH) deficiency is a form of central adrenal insufficiency caused by reduced secretion of adrenocorticotropic hormone by the corticotroph cells of the anterior pituitary, resulting in inadequate stimulation of the adrenal zona fasciculata and reduced production of cortisol. Unlike primary adrenal insufficiency, in which the damage is adrenal, in ACTH deficiency the adrenal gland is often structurally preserved but functionally “deprived” of the trophic signal, while aldosterone secretion is usually preserved because it is regulated predominantly by the renin-angiotensin system and serum potassium.
This condition may present as an isolated endocrinopathy or, more often, as part of hypopituitarism with multiple deficiencies. The most clinically critical element is that cortisol deficiency exposes the patient to the risk of adrenal crisis, especially during infections, surgical procedures, trauma, or inappropriate withdrawal of replacement therapy.
ACTH deficiency is not a single disease, but the common outcome of numerous conditions affecting the pituitary gland or the hypothalamic-pituitary unit. Its frequency in the general population is difficult to estimate precisely because it depends on the prevalence of the underlying pituitary diseases, the diagnostic strategies adopted, and clinical awareness in recognizing early, subclinical, or masked forms presenting with nonspecific symptoms. In clinical practice, epidemiology is strongly “driven” by high-risk settings: patients with pituitary adenomas, sequelae of sellar surgery, cranial radiotherapy, infiltrative or inflammatory diseases, and more recently patients treated with oncological immunotherapies.
Among the most relevant risk factors are expansive lesions of the sella turcica and parasellar region. Pituitary adenomas, especially macroadenomas, may cause corticotroph deficiency through compression of the residual parenchyma, altered vascularization, or sequelae of apoplexy. Similarly, craniopharyngiomas, parasellar meningiomas, and other lesions of the hypothalamic-pituitary region may impair ACTH secretion through compressive or infiltrative mechanisms, often in association with deficiencies of other axes.
A central category is represented by iatrogenic causes. Pituitary surgery may be followed by transient or permanent corticotroph insufficiency, depending on the disease treated, the extent of resection, and preoperative corticotroph reserve. Conventional or stereotactic radiotherapy to the sellar region is an important risk factor for progressive hypopituitarism, with deficiencies that may emerge even years later, making prolonged endocrinological follow-up necessary.
Inflammatory and autoimmune pituitary diseases, such as lymphocytic hypophysitis, may present with headache, visual disturbances, and hormonal dysfunction, and ACTH deficiency often represents one of the most dangerous elements in the acute setting. In women during pregnancy or in the postpartum period, some forms of hypophysitis acquire particular clinical relevance and require timely recognition.
In recent years, hypophysitis associated with immune checkpoint inhibitors has become increasingly relevant. In this setting, ACTH deficiency may present acutely or subacutely and may represent the main cause of systemic symptoms, sometimes in the absence of marked pituitary enlargement. Epidemiology varies according to the type of immunotherapy and combinations used, and clinical vigilance must be very high because cortisol deficiency may manifest with subtle signs but rapidly evolve into potentially life-threatening conditions.
Additional risk factors include head trauma, subarachnoid hemorrhage, and some vascular conditions that may alter pituitary perfusion. In obstetrics, Sheehan syndrome remains a historically important cause of hypopituitarism due to ischemic pituitary necrosis, with possible corticotroph deficiency of variable severity, although its frequency is strongly influenced by the quality of obstetric care and management of postpartum hemorrhage.
Finally, corticotroph deficiency must also be considered in the context of prolonged glucocorticoid therapy, which may suppress the hypothalamic-pituitary-adrenal axis. In this situation, the problem is not structural damage to the corticotrophs, but reduced ACTH secretion due to chronic negative feedback, with a risk of adrenal insufficiency in the event of rapid dose reduction or glucocorticoid withdrawal.
Pituitary ACTH deficiency results from functional or structural impairment of the corticotrophs of the anterior pituitary or of the regulatory circuits that control them. Under physiological conditions, ACTH secretion is governed by hypothalamic corticotropin-releasing hormone (CRH) and modulated by vasopressin, and is characterized by marked circadian rhythmicity and rapid responses to stress. This system maintains an adequate basal cortisol tone and, above all, rapidly increases cortisol production when the body is exposed to inflammatory, metabolic, or hemodynamic stress.
From an etiological standpoint, causes may be grouped into compressive, infiltrative, inflammatory, vascular, and iatrogenic forms. In compressive forms, the lesion mass reduces the amount of functioning corticotroph tissue and may interrupt hypothalamic signals through alterations of the pituitary stalk. In infiltrative forms, such as sarcoidosis, histiocytosis, or immunoglobulin G4 (IgG4)-related diseases, the parenchyma is replaced by inflammatory or fibrotic tissue, with progressive loss of hormone secretion and often multisystem involvement.
A crucial mechanism is functional insufficiency under stress. Even when basal cortisol production appears at the lower limit of normal, axis reserve may be inadequate, and the patient may fail to adapt to the demands imposed by fever, surgical procedures, or trauma. This explains why some patients remain paucisymptomatic at rest but experience sudden clinical deterioration under conditions of increased demand. In pathophysiological terms, ACTH deficiency reduces the adrenal gland’s ability to increase steroidogenesis and, over time, may reduce trophism of the zona fasciculata.
Preservation of aldosterone is a distinguishing feature compared with primary adrenal insufficiency. In most cases, patients with ACTH deficiency do not have significant hyperkalemia because mineralocorticoid secretion is maintained by angiotensin II and potassium. However, cortisol deficiency may still cause hyponatremia through combined mechanisms, including increased non-osmotic vasopressin secretion and reduced free-water clearance. Hyponatremia may become one of the most evident laboratory findings and, if not interpreted correctly, may point toward non-endocrine diagnoses.
At the metabolic and cardiovascular levels, cortisol is an essential regulator of vascular tone, response to catecholamines, gluconeogenesis, and immune modulation. Its deficiency may cause profound asthenia, reduced exercise tolerance, a tendency toward hypotension, and increased vulnerability to hypoglycemic episodes, especially in children or frail adults. At the immune level, the absence of cortisol’s permissive effect may amplify some inflammatory responses, while neuropsychiatric manifestations may include apathy, irritability, or reduced cognitive performance, often confused with primary psychiatric conditions or chronic illness syndromes.
Finally, when ACTH deficiency is part of broader hypopituitarism, pathophysiology becomes intrinsically systemic. The coexistence of central thyroid deficiency or growth hormone (GH) deficiency may amplify asthenia, weight changes, and frailty, while diagnosis and therapy require a reasoned sequence because starting thyroid replacement in a patient with untreated corticotroph insufficiency may precipitate adrenal crisis by increasing cortisol clearance and raising glucocorticoid requirements.
The clinical picture of ACTH deficiency is often subtle because many symptoms are nonspecific and overlap with common conditions such as functional anemia, depression, postoperative syndromes, or cancer-related fatigue. The distinguishing element is that these symptoms reflect reduced cortisol availability and, above all, a reduced ability of the body to respond to the physiological demands of stress. Presentation may range from a slowly progressive chronic condition to an acute onset, particularly in settings such as pituitary apoplexy, hypophysitis, or glucocorticoid withdrawal.
In the medical history, patients frequently report marked asthenia, reduced physical endurance, loss of appetite, unintentional weight loss, and difficulty maintaining usual daily rhythms. Nausea, abdominal discomfort, sometimes vomiting, and a feeling of “collapse” during fever or gastroenteritis may occur, with rapid worsening of general condition. In milder cases, the dominant symptom may be reduced ability to cope with emotional or occupational stress, with progressive deterioration in quality of life.
On physical examination, common findings include hypotension or an orthostatic tendency, cold skin, reduced overall performance, and sometimes signs of dehydration when concomitant fluid loss is present. A useful clinical feature is the absence, in most cases, of cutaneous or mucosal hyperpigmentation, which is typical of primary adrenal insufficiency. The absence of hyperpigmentation results from the fact that ACTH is not elevated, so there is no excess of proopiomelanocortin (POMC)-derived peptides capable of activating melanocortin receptors. This difference, although not absolute, contributes to differential clinical reasoning.
Metabolic manifestations may include a tendency toward hypoglycemia during prolonged fasting, especially in pediatric patients or patients with reduced nutritional reserves. In laboratory assessment, a relatively common finding is hyponatremia, which may be mild or significant and may sometimes be accompanied by neurological symptoms if it develops rapidly. Hyperkalemia, by contrast, is generally absent, and this represents an important orienting element when evaluating a patient with suspected adrenal insufficiency.
In patients with concomitant pituitary disease, clinical manifestations often include symptoms related to the sellar mass or to other hormonal deficiencies. Headache, visual field defects, reduced libido, amenorrhea, cold intolerance, or weight changes may coexist and mask the specific contribution of cortisol deficiency. In these cases, the endocrinological assessment must reconstruct the temporal sequence of symptoms and integrate the signs into a unified picture, avoiding fragmented interpretations.
The most severe presentation is adrenal crisis, which may manifest with severe hypotension, shock, intractable vomiting, altered mental status, hypoglycemia, and electrolyte disturbances. Crisis may occur in patients with known deficiency who have not adequately adjusted therapy during stress, or in undiagnosed patients in whom an acute event exceeds residual axis capacity. In this situation, the priority is immediate treatment, without waiting for definitive confirmation, because risk is time-dependent.
Suspicion of ACTH deficiency should arise when a patient presents symptoms compatible with cortisol deficiency in association with a plausible clinical context of pituitary dysfunction or suppression of the hypothalamic-pituitary-adrenal axis. In practice, suspicion is particularly strong in the presence of disproportionate asthenia and hypotension, especially if accompanied by hyponatremia, persistent nausea, or sudden worsening during trivial infections. The clinician must consider that corticotroph insufficiency may be “silent” until the first significant stress.
A high-risk group is represented by patients with a history of sellar surgery, cranial radiotherapy, or known pituitary lesions. In these cases, even subtle symptoms must be interpreted carefully because cortisol deficiency may manifest as reduced overall functional capacity, often incorrectly attributed to the postoperative course or the underlying disease. Similarly, patients with pituitary apoplexy may rapidly develop corticotroph insufficiency and present with intense headache, visual disturbances, and hemodynamic collapse.
Suspicion must also be high in oncology patients receiving immunotherapies that may induce hypophysitis or isolated corticotroph deficiency. In this context, the onset of fatigue, anorexia, nausea, or hypotension, even if interpreted as generic adverse effects, should prompt urgent assessment of cortisol, because the main clinical risk is glucocorticoid deficiency.
Another common situation is a history of prolonged use of systemic glucocorticoids or formulations with high systemic absorption, followed by rapid dose reduction or withdrawal. In these cases, symptoms may be subtle and may be confused with relapse of the treated disease, withdrawal syndrome, or intercurrent infections. Suspicion is particularly important when symptoms emerge within weeks or months of major changes in the glucocorticoid regimen.
Suspicion increases when signs of other pituitary deficiencies coexist, such as central hypothyroidism or hypogonadotropic hypogonadism. In these cases, the presence of “mixed” symptoms should not reduce diagnostic probability, but rather suggest a complete pituitary assessment. It is essential to remember that recognition of corticotroph insufficiency has practical priority, because its correction determines the safety of starting and adjusting other hormonal replacements.
In summary, ACTH deficiency should be suspected whenever symptoms compatible with cortisol deficiency occur in a patient with a biological or iatrogenic risk of hypothalamic-pituitary dysfunction, or when an apparently nonspecific clinical picture is accompanied by hyponatremia and hemodynamic instability without convincing alternative explanations.
Diagnosis of ACTH deficiency requires a sequential approach integrating clinical findings, basal tests, and dynamic tests, with the aim of demonstrating inadequate cortisol production due to a central defect and distinguishing this condition from primary adrenal insufficiency and other causes of hypocortisolism. The first step is assessment of morning cortisol, ideally sampled in the early morning hours, interpreted in the clinical context and considering that cortisol is a highly variable hormone influenced by stress, medications, and binding proteins.
Very low morning cortisol values in a symptomatic patient make adrenal insufficiency highly likely, while clearly adequate values make it unlikely. In the “intermediate” zone, where the basal value does not allow reliable conclusions, a stimulation test is necessary. In parallel, measurement of ACTH helps in the differential diagnosis: elevated ACTH points toward primary insufficiency, while low or inappropriately normal ACTH in the presence of reduced cortisol supports a central cause.
The most widely used test in practice is the cosyntropin test, using synthetic ACTH. It is useful for assessing the adrenal cortex’s ability to respond to an acute stimulus, but interpretation requires caution because in recent central deficiencies the adrenal gland may not yet be “atrophic” and the response may remain relatively preserved, generating false negatives. This is particularly relevant in the early period after pituitary surgery or after an acute pituitary event. For this reason, in selected situations, tests that more directly explore axis integrity are preferred.
The insulin tolerance test is traditionally considered a reference method for assessing the hypothalamic-pituitary-adrenal axis because it induces strong central stress capable of activating CRH, ACTH, and cortisol. However, it requires a protected setting and specific expertise because of the risks associated with hypoglycemia, and it is contraindicated in some patient categories. An alternative is the metyrapone test, which assesses axis response by inhibiting cortisol synthesis and inducing a compensatory increase in ACTH and steroid precursors; this test also requires experience and appropriate patient selection.
Beyond biochemical demonstration of insufficiency, etiological assessment is essential. The other pituitary axes must be evaluated with targeted measurements and, when indicated, hypothalamic-pituitary magnetic resonance imaging must be performed to identify adenomas, surgical sequelae, hypophysitis, infiltrative lesions, or pituitary stalk abnormalities. In patients receiving oncological immunotherapy, magnetic resonance imaging may be normal or may show variable signs that are not always correlated with the severity of corticotroph deficiency, so the decisive data often remain biochemical and clinical.
The differential diagnosis includes primary adrenal insufficiency, which tends to be more frequently associated with hyperkalemia and elevated ACTH, and adrenal insufficiency due to pharmacological suppression, in which interpretation of tests depends on the type of glucocorticoid used, duration of therapy, and time since the last dose. In potentially critical acute situations, the priority is to treat glucocorticoid deficiency and collect samples for cortisol and ACTH before therapy only if this does not delay treatment.
Classification of ACTH deficiency is clinically useful because it guides risk assessment, selection of diagnostic tests, and long-term management. A first fundamental distinction separates isolated forms from multiple forms. In isolated deficiency, the only impaired axis is the corticotroph axis, a situation described in some autoimmune or iatrogenic contexts, including a proportion of immunotherapy-related hypophysitis. In multiple forms, ACTH deficiency is associated with central thyroid-stimulating hormone (TSH) deficiency, gonadotropin deficiency, GH deficiency, and sometimes prolactin deficiency, forming a broader picture of hypopituitarism.
A second criterion distinguishes acute from chronic forms. Acute forms include pituitary apoplexy, fulminant hypophysitis, or sudden postoperative damage, and carry a high risk of adrenal crisis. Chronic forms, often due to sellar masses or radiotherapy, evolve slowly and may present with nonspecific symptoms, sometimes leading to delayed diagnosis. This distinction is important because in recent central deficiencies the adrenal response to synthetic ACTH testing may not yet reflect the true fragility of the axis under stress.
From a functional standpoint, severity may be conceptually framed as complete or partial insufficiency. In complete forms, cortisol production is clearly inadequate both at rest and under stress, and the patient requires stable replacement therapy. In partial forms, some patients maintain basal cortisol at the lower limits and may be relatively compensated in daily life, but fail to respond to stress; these patients require a careful strategy that may include low-dose replacement or at least a well-structured “stress” coverage plan, depending on biochemical evidence and clinical history.
Finally, a practical classification concerns organic versus functional pharmacological origin. In organic forms, the problem is pituitary or hypothalamic-pituitary damage; in pharmacological forms, the axis is suppressed by negative feedback from exogenous glucocorticoids. This latter category has specific implications because prognosis includes possible gradual recovery of the axis, and management must balance the risk of relapse of the treated disease with the risk of adrenal insufficiency, using dose reduction steps and dynamic reassessments.
Treatment of ACTH deficiency consists of glucocorticoid replacement and prevention of complications related to cortisol deficiency, with particular attention to stress management and prevention of adrenal crisis. The choice of medication, dosing schedule, and patient education are just as important as the dose itself, because long-term safety depends on the ability to adapt therapy to the dynamic conditions of real life.
In stable conditions, therapy is usually based on hydrocortisone in divided doses to approximate the physiological rhythm, with a larger dose in the morning and smaller doses in the afternoon, generally avoiding late administration that may interfere with sleep. Alternatives include low-dose prednisolone in single or twice-daily administration in selected patients when daily hydrocortisone management is problematic. Therapy must be personalized according to clinical findings, avoiding both undertreatment, which maintains asthenia and vulnerability to stress, and overtreatment, which promotes weight gain, hypertension, diabetes, and iatrogenic osteoporosis.
A cornerstone is management of stress situations. Fever, infections, trauma, and surgical procedures require a temporary increase in glucocorticoid dose. The patient must receive structured education on how to modify therapy in foreseeable situations and when to seek urgent evaluation. It is essential that the patient has a written and shared plan, and that family members know how to recognize warning signs.
Adrenal crisis is a medical emergency. In cases of clinical suspicion, parenteral hydrocortisone therapy and correction of hydroelectrolyte abnormalities must not be delayed. Treatment includes high-dose hydrocortisone and fluid therapy, with adjustments based on clinical response and hemodynamic recovery. In this phase, stabilization is the priority, while etiological definition and dynamic evaluations can be completed subsequently.
Since aldosterone is generally preserved in central deficiency, mineralocorticoid therapy is usually not necessary. However, the patient may still present with hypotension and hyponatremia related to cortisol deficiency; correction usually occurs with adequate glucocorticoid replacement and management of the precipitating event, rather than with fludrocortisone. In cases with multiple pituitary deficiencies, therapy must follow a safe sequence: glucocorticoid coverage must be ensured before starting or increasing thyroid replacement.
When ACTH deficiency is secondary to a treatable pituitary disease, etiological therapy may include surgery, radiotherapy, or immunosuppressive treatment in selected situations such as some forms of hypophysitis. In all cases, the presence of corticotroph deficiency requires rigorous perioperative and periprocedural management, with adequate coverage and postoperative reassessment to determine whether the axis recovers or whether replacement must become permanent.
Follow-up of ACTH deficiency has three main objectives: to ensure effective and safe replacement, to prevent and recognize adrenal crises early, and to assess the evolution of the axis over time, including the possibility of recovery in selected contexts. Monitoring cannot rely exclusively on hormone measurements, because cortisol values are not easily interpretable during replacement therapy and because clinical outcome depends largely on stress management.
Periodic assessment must include analysis of symptoms compatible with undertreatment, such as persistent asthenia, orthostatic hypotension, and reduced exercise tolerance, as well as signs of overtreatment, such as weight gain, hypertension, hyperglycemia, skin fragility, and sleep disturbances. It is particularly important to reconstruct any intercurrent episodes, emergency department visits, significant infections, and how the patient adjusted doses, because these data often reveal educational rather than pharmacological critical points.
An essential component of follow-up is continuous education of the patient and caregivers. Availability of a medical card or clinical document, use of alert devices, and access to parenteral hydrocortisone for emergencies, when indicated, reduce the risk of severe outcomes. Follow-up must concretely verify that the patient can recognize warning signs and can administer or promptly request appropriate therapy.
In patients with pituitary diseases, follow-up must include surveillance of the sellar lesion with imaging when indicated and reassessment of the other pituitary axes, because function may progressively worsen, particularly after radiotherapy. Management must be coordinated, since changes in other hormonal treatments may influence glucocorticoid requirements and clinical stability.
When the deficiency is potentially reversible, such as after gradual withdrawal of glucocorticoids or in some forms of hypophysitis, it is appropriate to plan axis reassessment at intervals consistent with the physiology of recovery. This reassessment requires washout windows and selected dynamic tests, performed safely, with expert interpretation and coverage plans during the transition period. The goal is to avoid both premature discontinuation that exposes the patient to crisis and unnecessarily prolonged replacement.
The prognosis of ACTH deficiency is generally good when the diagnosis is made correctly and replacement therapy is managed competently, because cortisol replacement allows substantial functional recovery and good quality of life in most cases. However, prognosis depends critically on two factors: the ability to prevent and promptly treat adrenal crises and the management of the underlying pituitary disease, which may cause further hormonal deficiencies or neurological and ophthalmological problems.
The most important complication, both in terms of severity and preventability, is adrenal crisis. Risk increases in the presence of gastrointestinal infections with vomiting, high fever, surgical procedures, trauma, and all situations in which oral intake is reduced or absent. In patients with multiple deficiencies, crisis may also be precipitated by unprotected therapeutic changes, particularly starting or increasing thyroid replacement without adequate glucocorticoid coverage. Prevention requires education, stress-dosing plans, and facilitated access to urgent care.
Another area of complications concerns chronic overtreatment. Even only moderately excessive doses, if continued over time, may promote central obesity, metabolic derangement, reduced bone mass, and increased cardiovascular risk. Since glucocorticoid replacement does not perfectly reproduce the circadian physiology of cortisol, part of management consists of optimizing the regimen to minimize adverse effects while maintaining adequate protection during the most active hours and in stress settings.
Complications related to the causal disease include adenoma progression, recurrence, radiotherapy sequelae, and persistent hypophysitis, which may cause worsening of other axes and the need for additional treatments. In oncology patients, overall prognosis also depends on the oncological pathway and the adverse effects of immunotherapy, but timely correction of cortisol deficiency remains crucial to prevent severe acute events and reduce unnecessary treatment interruptions.
Overall, ACTH deficiency is a condition with high clinical impact, especially because of acute risk, but it has a favorable outcome when managed through a structured approach centered on correct diagnosis, personalized replacement, education, and continuous monitoring.