Excess ACTH (adrenocorticotropic hormone) defines a group of conditions in which chronic stimulation of the adrenal cortex causes persistent hypercortisolism and loss of the physiological circadian rhythm of cortisol. Within endogenous Cushing syndrome, the most frequent cause of ACTH-dependent hypercortisolism is Cushing disease, sustained by an ACTH-secreting corticotroph pituitary adenoma; a clinically more insidious relevant proportion is represented by ectopic ACTH secretion from non-pituitary neoplasms. The shared element is systemic exposure to inappropriately elevated glucocorticoids, with multisystem consequences involving metabolism, the cardiovascular system, bone, muscle, skin, the immune system and the neuropsychiatric axis.
Recognition of ACTH excess requires an approach that integrates the clinical phenotype, dynamic biochemistry and etiological localization. The main difficulty is not only demonstrating hypercortisolism, but distinguishing true forms from pseudo-Cushing states and, after biochemical confirmation, correctly attributing the source of ACTH in order to guide curative treatment whenever possible.
Endogenous Cushing syndrome is a rare condition, but it has a high clinical impact because hypercortisolism is associated with a documented increase in mortality and cardiovascular, thromboembolic and infectious morbidity, with a burden of comorbidities that often precedes diagnosis by years. In modern case series and reviews, the incidence of endogenous forms is in the range of a few cases per million people per year, with a distribution that varies according to national registries and inclusion criteria. Cushing disease represents the main cause of ACTH-dependent endogenous hypercortisolism, whereas ectopic ACTH secretion is numerically less frequent but clinically relevant because of its severity, rapid evolution and the difficulty of localizing the tumor source.
From a demographic perspective, Cushing disease shows a female predominance in adulthood, whereas in children and adolescents the distribution may be less unbalanced and the clinical picture is influenced by the growth phase, with growth deceleration and weight gain as key signs. Clinical presentation is also conditioned by the intensity and duration of hypercortisolism: slowly developing forms, with mild or intermittent hypercortisolism, may be missed and mistaken for common metabolic phenotypes, whereas more aggressive forms, typically related to ectopic secretion or adenomas with high activity, cause rapid deterioration with hypokalemia, opportunistic infections and marked myopathy.
The risk factors for ACTH excess are not configured as linear environmental exposures, but as probabilities linked to the presence of specific neoplasms and, in a minority of cases, genetic predispositions. In the pituitary context, most cases are sporadic; however, rare hereditary syndromes may include functioning pituitary adenomas within their spectrum. On the ectopic side, risk is connected to the presence of neuroendocrine tumors or carcinomas capable of expressing the transcriptional program of pro-opiomelanocortin (POMC) and processing it into biologically active ACTH. In practical terms, a clinical history suggesting neuroendocrine neoplasms, pulmonary lesions, thymic or pancreatic tumors, or particularly rapid clinical progression increases the pre-test probability of an ectopic form.
A crucial point in clinical epidemiology is that many people with signs suggestive of hypercortisolism actually have much more frequent conditions that partially mimic the phenotype, such as obesity, type 2 diabetes, depression, alcohol abuse or obstructive sleep apnea. This overlap generates a broad population in which true ACTH excess is rare, but in which correct selection of patients to undergo diagnostic testing is decisive for reducing false positives and unnecessary pathways, while maintaining high sensitivity in clinically progressive forms or in those with highly specific phenotypic features.
ACTH excess leading to ACTH-dependent Cushing syndrome derives, by definition, from ACTH secretion that is inappropriate relative to the negative feedback of glucocorticoids. Physiologically, the hypothalamus releases CRH and vasopressin, which stimulate pituitary corticotrophs to produce ACTH from the POMC precursor; ACTH activates the melanocortin 2 receptor (MC2R) in the adrenal zona fasciculata, inducing steroidogenesis and maintaining cortical trophism. Cortisol, in turn, inhibits CRH and ACTH, preserving homeostasis and circadian rhythms. In Cushing disease, a corticotroph adenoma loses physiological sensitivity to feedback and secretes ACTH with a pathological set point; in ectopic secretion, extrapituitary tumor cells acquire the ability to express POMC and release ACTH, often in a non-rhythmic and non-modulable manner.
In pituitary corticotroph adenoma, pathogenesis includes molecular events that promote proliferation and secretion. A significant proportion shows somatic mutations in genes involved in receptor trafficking and degradation, with increased proliferative signaling and ACTH production. These alterations translate into chronic adrenal hyperstimulation and cortisol secretion that tends to lose its normal diurnal oscillation, with increased evening and nocturnal cortisol. Loss of rhythmicity is not a quantitative detail, but a central pathophysiological element: target tissue is exposed to a “flat” glucocorticoid signal, which alters the expression of genes regulated by the glucocorticoid receptor and disrupts the circadian orchestration of metabolism, immunity and cardiovascular function.
In ectopic forms, pathophysiology is often dominated by very high ACTH concentrations, with severe and rapid hypercortisolism. The adrenal cortex responds with hyperplasia and enhancement of steroidogenesis, leading to cortisol concentrations capable of saturating peripheral inactivation mechanisms and amplifying functional mineralocorticoid effects. In particular, cortisol excess can exceed the capacity of 11β-hydroxysteroid dehydrogenase type 2 to convert cortisol into cortisone in sensitive tissues, allowing activation of the mineralocorticoid receptor and promoting hypertension, sodium retention and hypokalemia, often marked in ectopic forms.
The systemic effects of hypercortisolism are the result of glucocorticoid receptor action in multiple districts. In the liver and muscle, gluconeogenesis increases and peripheral glucose utilization decreases, with insulin resistance and diabetes; in adipose tissue, lipolysis and fat redistribution promote visceral adiposity and steatosis, while leptin resistance and adipocytokine dysfunction amplify metabolic inflammation. In bone, osteoblast inhibition and increased resorption, together with relative hypogonadism and reduced muscle mass, lead to osteoporosis and fragility fractures even at a relatively young age. In the cardiovascular system, hypertension, dyslipidemia, endothelial dysfunction and a prothrombotic state contribute to an elevated risk of major events; on the immune level, suppression of cell-mediated responses increases susceptibility to infections and reduces the typical inflammatory presentation, making some clinical pictures subtle.
A clinically relevant aspect is the dissociation between “quantity” and “damage”: even moderately elevated but chronic levels can produce a deep pathophysiological imprint if exposure is prolonged and if circadian rhythmicity is lost. This explains why slowly developing forms can cause significant disability and why, even after remission, some alterations such as myopathy, bone fragility and neurocognitive disorders may persist for months or years, requiring rehabilitation strategies and long-term risk reduction.
The history in ACTH excess must reconstruct the temporal progression of signs and symptoms, because dynamics are often discriminating. The patient typically reports weight gain with centripetal redistribution, reduced exercise tolerance and proximal weakness, sometimes with difficulty climbing stairs or rising from a seated position, as well as easy fatigability. The onset of newly diagnosed hypertension or diabetes, especially if rapidly worsening or difficult to control, is frequent. In women, menstrual irregularities, reduced fertility and hirsutism are common; in men, reduced libido and erectile dysfunction may emerge, with loss of muscle mass. On the neuropsychiatric side, mood disorders, irritability, insomnia, reduced concentration and worsening quality of life are extremely frequent and may represent the main reason for consultation.
During physical examination, some signs have greater discriminating power than common metabolic phenotypes. The skin may appear thin and fragile, with ecchymoses after minimal trauma and delayed wound healing; broad striae rubrae, especially on the abdomen, flanks and thighs, reflect an alteration of connective tissue and are not equivalent to simple stretch marks. The face may become full and flushed, with plethora and acne; fat distribution is characterized by increased truncal and cervicodorsal adiposity. Proximal myopathy is often evident during functional maneuvers, whereas muscle atrophy of the limbs and reduced strength may be disproportionate to overall body mass.
Hypercortisolism also affects blood pressure and the cardiovascular system, with hypertension that is often persistent and sometimes associated with edema. In the most severe forms, especially ectopic forms, hypokalemia may cause cramps, marked asthenia and electrocardiographic abnormalities, requiring immediate assessment of electrolyte balance. Susceptibility to infection increases and infections may present with attenuated signs; a history of recurrent infections, candidiasis or unexplained exacerbations must be considered part of the clinical picture.
In children, the combination of weight gain and growth deceleration is particularly suggestive and should prompt timely assessment, because the consequences for bone, pubertal development and cardiometabolic profile may be relevant. At any age, a history of low-energy fractures, back pain or height loss suggests vertebral fragility fractures, often underdiagnosed, and requires targeted assessment of skeletal health.
Clinical suspicion must be based on the combination of progressiveness and the presence of signs with high discriminating value. ACTH excess should be considered when multiple evolving manifestations coexist, particularly if the patient rapidly develops hypertension, diabetes, osteoporosis or skin fragility, or if typical signs appear, such as broad striae rubrae, frequent ecchymoses, proximal myopathy and facial plethora. Another important scenario is the association with an adrenal incidentaloma or with an oncological history that increases the probability of ectopic secretion.
Suspicion must also be high when common comorbidities show atypical behavior, such as suddenly unstable diabetes, resistant hypertension or rapid worsening of sarcopenia. In more severe contexts, the combination of clinical hypercortisolism with hypokalemia, edema, recurrent infections and loss of muscle mass suggests a severe form, often ectopic, requiring an accelerated pathway to reduce the time of exposure to cortisol.
At the same time, it is essential to identify the contexts in which indiscriminate testing produces false positives. Conditions such as major depression, alcoholism, severe obesity, chronic stress and some systemic diseases may cause partially overlapping biochemical alterations. In these cases, patient selection and interpretation of the clinical profile become central: rather than a single symptom, it is the coherence of the picture over time, with specific and progressive physical signs, that justifies a complete endocrinological evaluation.
Diagnosis proceeds in two conceptual phases: first, confirmation of hypercortisolism, then etiological attribution by distinguishing ACTH-dependent from ACTH-independent forms, and finally localization of the ACTH source. The first indispensable step is exclusion of exogenous glucocorticoid use, including systemic medications, injections, high-absorption topical preparations and some inhaled formulations at high doses. After this exclusion, high-accuracy screening tests are performed.
According to the Endocrine Society guidelines, to diagnose endogenous Cushing syndrome it is necessary to start with at least one test among urinary free cortisol (24-hour collection), late-night salivary cortisol, overnight 1 mg dexamethasone suppression test or 2 mg dexamethasone for 48 hours, and in the event of an abnormal result to perform a second confirmatory method, preferably of a different class, before proceeding to search for the cause. The rationale is to reduce the impact of biological variability and analytical interference: hypercortisolism is a dynamic condition and its diagnosis cannot rely on a single isolated value.
Once hypercortisolism has been documented with concordantly abnormal results, the next step is measurement of plasma ACTH, interpreted contextually and repeated when necessary. Low or suppressed ACTH suggests an ACTH-independent form, whereas measurable or elevated ACTH supports an ACTH-dependent form, which includes Cushing disease and ectopic secretion. In the case of ACTH dependence, the strategy aims to distinguish pituitary origin from ectopia: this phase combines clinical elements (severity, hypokalemia, speed of progression), selected dynamic tests and anatomical localization.
Pituitary imaging with high-resolution magnetic resonance imaging is an important step, but it is not decisive on its own, because microadenomas may not be visible and incidental lesions may be present in subjects without disease. For this reason, when magnetic resonance imaging does not show a convincing lesion or when biochemical results are discordant, the reference method for demonstrating a pituitary origin of ACTH is inferior petrosal sinus sampling with determination of the central-to-peripheral gradient, often in association with stimulation by CRH or desmopressin, according to center protocols. This examination allows discrimination, with high accuracy, between pituitary ACTH excess and ectopic ACTH excess, reducing the risk of unnecessary surgery or therapeutic delays.
When the etiology is ectopic or suspected to be ectopic, diagnostic imaging extends to the chest and abdomen with tomography or magnetic resonance imaging, and in selected cases to functional methods targeted at neuroendocrine tumors. Localization may be complex, because some neoplasms are small and secretion may be intermittent. In these situations, management requires a balance between diagnostic investigation and rapid control of hypercortisolism, because prolonged exposure to cortisol is the main determinant of acute and chronic complications.
Throughout the diagnostic pathway, pre-analytical and analytical interference must be considered: medications that alter dexamethasone metabolism, variability of urinary free cortisol, sleep disorders that influence nocturnal cortisol, and conditions that simulate hypercortisolism. The final result must be not only a “biochemical” diagnosis, but an etiological diagnosis, because therapeutic choice depends on the ACTH source and on the possibility of curative treatment.
The main classification of hypercortisolism separates exogenous forms from endogenous forms; within endogenous forms, the fundamental distinction is between ACTH-independent and ACTH-dependent Cushing syndrome. This page focuses on ACTH-dependent forms, which include pituitary Cushing disease and ectopic ACTH secretion. The difference is not only anatomical: pituitary secretion is often more gradual and may present with a “classic” phenotype, whereas ectopia may cause rapidly progressive pictures, with hypokalemia, severe myopathy and high infectious risk.
On the clinical expression level, there is a continuum of severity. Mild or intermittent forms may manifest with partial signs, often dominated by dysmetabolism and bone fragility, and require accurate interpretation of tests, with attention to reproducibility. At the opposite end, severe forms present with marked hypercortisolism and acute complications that make cortisol control a priority even before complete etiological definition. In a minority of cases, hypercortisolism may be cyclic, with phases of hypersecretion alternating with periods of apparent normality; this variability requires repeated diagnostic strategies based on symptoms and timing of sampling.
From an anatomopathological perspective, Cushing disease is sustained by corticotroph adenomas that are often microadenomas; less frequently, by macroadenomas with invasive features. Ectopic ACTH secretion, instead, is associated with neuroendocrine tumors, especially pulmonary and thymic tumors, but it may also be produced by other neoplasms. Classification must always include assessment of comorbidities and risk: thrombotic state, severity of hypertension, glycemic control, skeletal integrity and infectious vulnerability represent clinical dimensions that determine treatment priorities and intensity, independently of the ACTH source.
Treatment has two integrated objectives: etiological cure whenever possible and rapid control of hypercortisolism to reduce the risk of complications. In Cushing disease, first-line treatment is transsphenoidal pituitary surgery performed in highly experienced centers, because success critically depends on the quality of exploration and perioperative management. Remission is assessed by monitoring cortisol in the early postoperative phases and during follow-up, taking into account that transient adrenocortical insufficiency may represent a marker of disease control but requires glucocorticoid replacement and a gradual tapering plan. Recurrence remains a concrete possibility and requires long-term surveillance even after apparent cure.
When surgery is not curative, is not feasible or while awaiting definitive treatment, pharmacological therapy plays a central role. Strategies are organized by target: agents that reduce adrenal steroidogenesis, agents that modulate pituitary ACTH secretion and glucocorticoid receptor antagonists. Steroidogenesis inhibitors, including historical and more recent molecules, reduce circulating cortisol and may achieve rapid control, but require close monitoring for the risk of iatrogenic adrenal insufficiency, electrolyte abnormalities and pharmacological interactions. Newer molecules have expanded therapeutic options, especially in refractory cases or when sustained control is required.
In the pituitary context, some medications act at the tumor level, modulating ACTH secretion and, in some cases, reducing adenomatous volume. The choice is guided by efficacy profile, tolerability and comorbidities, considering that hyperglycemia, gastrointestinal disorders and cardiac alterations may influence treatment sustainability. Antagonism of the glucocorticoid receptor represents a conceptually different approach: it improves the clinical signs of glucocorticoid excess without directly reducing cortisol, making clinical-metabolic monitoring and surveillance for specific adverse effects essential, including electrolyte imbalance and, in women, effects on the endometrium.
In cases of ectopic ACTH secretion, curative treatment is resection or oncological control of the responsible neoplasm when it is identified and treatable. However, localization may require time, and the severity of hypercortisolism may impose immediate pharmacological control of cortisol to reduce acute complications, especially infectious and thrombotic complications. In refractory cases or when adequate control cannot be obtained with medications, bilateral adrenalectomy may be an effective salvage strategy to eliminate cortisol production, at the cost of permanent glucocorticoid and mineralocorticoid replacement and the risk of Nelson syndrome in the case of pituitary origin.
Regardless of etiology, treatment must include aggressive management of comorbidities: blood pressure control, diabetes treatment, osteoporosis prevention and reduction of thromboembolic risk in selected contexts. Hypercortisolism is a prothrombotic and immunosuppressive state, so assessment of thrombotic and infectious risk is an integral part of treatment and not an accessory aspect.
Follow-up is essential because Cushing disease and, more generally, ACTH excess can recur even after a prolonged period of remission. After pituitary surgery, monitoring is based on serial clinical and biochemical evaluations, with attention to recovery of the hypothalamic-pituitary-adrenal axis and the need for temporary glucocorticoid replacement. Management of post-treatment adrenal insufficiency requires patient education, a stress-dose plan and early recognition of signs of adrenal crisis, because the transition period between hypercortisolism and normalization may be clinically fragile.
Over time, surveillance must include assessment of the recurrence of clinical signs and targeted testing for hypercortisolism when indicated. Tests such as late-night salivary cortisol and urinary free cortisol may be used repeatedly to intercept recurrence early, especially when there is a history of cyclic disease or when the patient has a clinical phenotype that tends to re-emerge gradually. Pituitary imaging has a complementary role and is interpreted together with biochemical data, avoiding decisions based on isolated radiological findings.
A central axis of follow-up is management of sequelae. Even after biochemical remission, many people maintain a high prevalence of hypertension, dysmetabolism, reduced muscle performance, sleep disorders and bone fragility. For this reason, monitoring must include periodic assessments of bone mineral density, fracture risk, cardiometabolic profile and mental health, integrating rehabilitation pathways for myopathy and functional recovery strategies. Follow-up must be conceived as a process of long-term risk reduction, not as simple laboratory confirmation of remission.
Prognosis mainly depends on the duration and severity of cortisol exposure, the speed with which control of hypercortisolism is achieved and the management of comorbidities. Summary evidence shows that endogenous hypercortisolism is associated with an increase in cardiovascular events and mortality, and that remission reduces risk but does not immediately erase the pathophysiological imprint, especially if exposure has been prolonged. In severe forms, particularly ectopic forms, the risk of acute complications is high and requires timely therapeutic control.
The main complications include hypertension and cardiovascular damage, venous thromboembolism, severe infections, worsening of glycemic control, osteoporosis and fractures, myopathy with functional loss, neuropsychiatric disorders and cognitive impairment. A specific risk of the treatment pathway is post-treatment adrenal insufficiency, which may manifest with asthenia, hypotension, nausea and hypoglycemia and becomes dangerous under stress conditions if not adequately managed with replacement therapy and patient instruction. In the case of bilateral adrenalectomy, dependence on replacement is permanent and requires structured follow-up.
In Cushing disease, recurrence represents a relevant prognostic complication, because it exposes the patient again to the effects of hypercortisolism. In addition, after repeated pituitary treatments or radiotherapy, multiple pituitary deficits may appear, requiring hormone replacement and specialist monitoring. In some patients, quality of life remains reduced even in remission because of muscular, skeletal and psychological sequelae, making a long-term multidisciplinary approach indispensable.
In summary, effective control of ACTH excess significantly improves outcome, but optimal prognosis requires timely diagnosis, treatment in expert centers, prolonged surveillance and targeted interventions on the comorbidities that hypercortisolism has induced or aggravated.