Cushing Syndrome and Cushing Disease

Core concept: Cushing syndrome is chronic pathologic glucocorticoid excess from any cause; Cushing disease refers specifically to an ACTH-secreting pituitary adenoma.

Key clinical distinction: All patients with Cushing disease have Cushing syndrome, but exogenous steroid use, adrenal autonomous secretion, and ectopic ACTH can also cause Cushing syndrome.

Clinical priority: Look for disproportionate proximal weakness, fragility fractures, infection, severe hyperglycemia, thromboembolism, or difficult hypertension; identify exogenous glucocorticoid exposure before biochemical screening.

Etiology and Epidemiology

Iatrogenic glucocorticoid exposure is a frequent explanation for Cushingoid features and must be assessed across oral, injected, inhaled, and topical routes. Endogenous cortisol excess is ACTH-independent when the adrenal gland secretes autonomously, or ACTH-dependent when the pituitary or an ectopic tumor provides inappropriate ACTH stimulation. Obesity, depression, alcohol-related physiology, poorly controlled diabetes, and other stress states may cause overlapping features or physiologic cortisol activation (Else & Hammer, 2019).

Pathophysiology

Sustained cortisol excess increases hepatic glucose output, impairs insulin sensitivity, and accelerates skeletal muscle and skin protein breakdown. The resulting central adiposity with thin extremities, proximal weakness, slow wound repair, broad violaceous striae, and fragility fractures is more discriminating than weight gain alone. Cortisol also increases vascular responsiveness and may overwhelm mineralocorticoid protection, contributing to hypertension; immune and gonadal suppression explain infection risk and menstrual or sexual dysfunction.

Cortisol excess normally suppresses CRH and ACTH. Exogenous or adrenal-driven excess commonly produces suppressed ACTH; pituitary or ectopic ACTH production remains inappropriately high despite hypercortisolism. Pituitary ACTH excess can cause bilateral adrenal stimulation, while adrenal autonomous secretion generally suppresses pituitary ACTH.

Clinical Manifestations

Discriminating findings include wide violaceous striae, proximal myopathy, thin easily bruised skin, poor wound healing, early osteoporosis, and unexplained metabolic clustering. Other manifestations include central weight gain, hypertension, glucose intolerance or diabetes, menstrual disturbance, low libido, infection susceptibility, depression, and impaired cognition. Isolated obesity or fatigue is not specific.

Diagnostic Evaluation

After excluding exogenous glucocorticoids and identifying a meaningful pretest probability, initial testing should use a validated strategy: at least two urine-free cortisol collections, at least two late-night salivary cortisol samples, or dexamethasone suppression testing as appropriate. Random cortisol and ACTH are not diagnostic screening tests. Test selection and interpretation must consider circadian disruption, assay limitations, estrogen exposure, and medications that alter dexamethasone metabolism. Concordant normal results argue against Cushing syndrome in most noncyclic presentations; discordant results require reassessment or specialist testing, not immediate pituitary imaging (Nieman et al., 2008).

Interpret apparent hypercortisolism within its context: Shift work or irregular sleep impairs the rationale for a midnight cortisol test; oral estrogen can increase cortisol-binding globulin and affect total serum cortisol after dexamethasone; drugs affecting dexamethasone metabolism can produce misleading suppression results. Alcohol-related illness, severe depression, and other nonneoplastic stress states may temporarily activate the axis. When biochemical and clinical findings diverge, do not move directly to MRI merely to settle the ambiguity.

Localize only after confirming endogenous cortisol excess. Suppressed ACTH favors an adrenal source; consistently nonsuppressed ACTH requires distinction between pituitary and ectopic ACTH secretion. A pituitary MRI lesion may be incidental, while a true ACTH-producing microadenoma may be radiographically occult. Imaging is therefore supportive only after biochemical confirmation. Specialist dynamic evaluation and, in selected cases, inferior petrosal sinus sampling can resolve biochemical–imaging discordance; sampling is not a screening test for hypercortisolism (Penman et al., 2023).

Management Principles

Address the source: safely adjust exogenous exposure where feasible without abrupt steroid withdrawal; consider pituitary surgery for Cushing disease or appropriate adrenal/ectopic-source treatment after localization. Medical inhibition of cortisol synthesis or action and complication management may be used in selected situations. Risk mitigation includes evaluating blood pressure, glucose, bone disease, infection, thromboembolism, and psychiatric burden. Treated patients may develop transient or prolonged adrenal insufficiency (Nieman et al., 2015; Polomoff et al., 2026).

Clinical Reasoning Priorities

Clinical sequence: A patient has progressive proximal weakness, spontaneous bruising, broad striae, and difficult hypertension. Two correctly collected screening tests are abnormal. Before ordering a pituitary scan, verify the absence of exogenous exposure and measure ACTH. Suppressed ACTH shifts the evaluation toward adrenal autonomy; nonsuppressed ACTH requires pituitary-versus-ectopic evaluation rather than automatic attribution to Cushing disease.

Diagnostic uncertainty: A patient has obesity and depression, one borderline abnormal late-night salivary cortisol, and a 4-mm pituitary focus found incidentally. Neither finding establishes Cushing disease. Clarify the sleep schedule, assay and collection quality, physiologic confounders, and whether additional validated biochemical testing supports pathologic cortisol excess; imaging cannot substitute for endocrine confirmation.

High-Yield Distinctions

Syndrome describes the cortisol-excess phenotype; disease describes a pituitary ACTH adenoma.
An adrenal cortisol-producing tumor suppresses ACTH; a pituitary ACTH-producing tumor does not.
Biochemical testing comes before anatomic imaging in suspected endogenous Cushing syndrome.

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Content last reviewed:

October 24, 2026

References

Else, T., & Hammer, G. D. (2019). Disorders of the adrenal cortex. In G. D. Hammer & S. J. McPhee (Eds.), Pathophysiology of disease: An introduction to clinical medicine (8th ed., Chapter 21). McGraw-Hill Education.

Nieman, L. K., Biller, B. M. K., Findling, J. W., Newell-Price, J., Savage, M. O., Stewart, P. M., & Montori, V. M. (2008). The diagnosis of Cushing’s syndrome: An Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology & Metabolism, 93(5), 1526–1540. https://doi.org/10.1210/jc.2008-0125

Nieman, L. K., Biller, B. M. K., Findling, J. W., Murad, M. H., Newell-Price, J., Savage, M. O., & Tabarin, A. (2015). Treatment of Cushing’s syndrome: An Endocrine Society clinical practice guideline. The Journal of Clinical Endocrinology & Metabolism, 100(8), 2807–2831. https://doi.org/10.1210/jc.2015-1818

Penman, I. D., Ralston, S. H., Strachan, M. W. J., & Hobson, R. P. (Eds.). (2023). Davidson’s principles and practice of medicine (24th ed.). Elsevier.

Polomoff, C. M., Chen, J. T., & Dang, D. K. (2026). Adrenal gland disorders. In M. A. Chisholm-Burns, J. M. Kolesar, P. M. Malone, K. C. Lee, B. P. Bookstaver, & K. R. Matthias (Eds.), Pharmacotherapy principles & practice (7th ed., Chapter 46). McGraw Hill.