Cushing Syndrome

Cushing syndrome is the clinical syndrome produced by chronic exposure to excess glucocorticoid, from any source. By far the most common cause overall is exogenous (iatrogenic) corticosteroid therapy — an estimated 1% or more of the adult population in high-income countries is on chronic glucocorticoid therapy at any given time, a population many times larger than the pool of patients with a true endogenous hypercortisolism-producing tumor.^[1] Endogenous Cushing syndrome is rare and is classified by whether ACTH drives it: ACTH-dependent disease (about 80-85% of endogenous cases) is caused by a pituitary corticotroph adenoma — this specific entity is called Cushing's disease and accounts for roughly three-quarters to four-fifths of ACTH-dependent cases, with most of the remainder from an ectopic ACTH-secreting tumor (most often a bronchial carcinoid); ACTH-independent disease (about 15-20% of endogenous cases) arises directly from the adrenal cortex — a cortisol-producing adenoma, adrenocortical carcinoma, or primary bilateral adrenal hyperplasia. Cushing's disease itself is estimated to occur in only about 1.2-1.8 people per million per year.^[2]

Whatever the source, the downstream physiology is the same: sustained glucocorticoid excess drives fat redistribution, catabolism of muscle and skin collagen, insulin resistance, sodium retention and hypertension, bone loss, immunosuppression, and mood disturbance. This chapter treats the endogenous causes and their surgical/medical management in detail, but its central practical message is that the pharmacist's most common encounter with Cushing syndrome is the iatrogenic form — a patient whose chronic prescribed corticosteroid has itself produced the syndrome — and the priorities there are recognizing cumulative exposure across every route of administration, never stopping the causative steroid abruptly, and reinforcing the same metabolic and bone-health monitoring that applies regardless of cause.

• Exogenous (iatrogenic) corticosteroid therapy at a supraphysiologic dose and/or duration, by any route — oral, high-potency topical, intra-articular or epidural injection, inhaled, or intranasal — is by far the most common cause of Cushing syndrome overall.^[1] Risk scales with potency, dose, and duration: a pooled meta-analysis found HPA-axis-suppression prevalence ranging from about 4% with intranasal corticosteroid use up to about 52% with intra-articular/epidural injection, with inhaled-corticosteroid-only asthma patients averaging 6.8% but rising to 21.5% at high inhaled doses and 27.4% after more than 1 year of continuous use.^[4]
• A new drug interaction added to an existing, previously well-tolerated corticosteroid — strong CYP3A4 inhibitors (ritonavir and other boosted HIV protease inhibitors, itraconazole, and even moderate inhibitors such as some SSRIs) can precipitate clinical iatrogenic Cushing syndrome without any change in the corticosteroid dose itself, since several commonly used corticosteroids (fluticasone, budesonide) depend heavily on CYP3A4 for clearance.^[4]
• Cushing's disease — a pituitary corticotroph adenoma — the most common endogenous cause, typically presenting in adults 25-45 years old and more common in women.
• Ectopic ACTH-secreting tumor — most often a bronchial carcinoid; also small cell lung cancer, pancreatic neuroendocrine tumor, medullary thyroid carcinoma, or pheochromocytoma. Skews toward an older population and, with an aggressive malignancy, a more rapid and severe presentation.
• Adrenal cortisol-producing adenoma or adrenocortical carcinoma — carcinoma typically presents with a larger mass, faster onset, and more pronounced androgen co-secretion than a benign adenoma.
• Primary bilateral (macronodular or micronodular) adrenal hyperplasia — less common ACTH-independent causes, occasionally with a genetic basis (McCune-Albright syndrome, Carney complex, or a familial isolated micronodular hyperplasia syndrome).

Also refer to endocrinology for any newly suspected endogenous Cushing syndrome (confirmatory biochemical testing, localization imaging, and surgical planning should not be managed outside specialist care); any patient whose chronic glucocorticoid therapy genuinely cannot be reduced despite significant Cushingoid complications, to discuss a steroid-sparing strategy with the prescribing specialty; and any patient being considered for medical therapy or bilateral adrenalectomy.

First: rule out an exogenous source before testing for endogenous disease

Before ordering any biochemical workup, take a complete inventory of every corticosteroid-containing product the patient uses — oral, topical, inhaled, intranasal, injected, and any compounded or unregulated product — since patients frequently do not think to mention a topical, inhaled, or injected product as "medication," and ask specifically about any recently added interacting drug (see Risk Factors). If a supraphysiologic exogenous source adequately explains the clinical picture, biochemical testing for endogenous disease is unnecessary and can be actively misleading — proceed directly to the iatrogenic management pathway (Clinical Decision Algorithm, Algorithm D).^[1]

First-line screening, if no exogenous source explains the picture

Per the Endocrine Society diagnostic guideline, use at least 2 of the following 3 first-line tests, with abnormal results confirmed by repeat or a second different test before proceeding to localization:^[5]

• 24-hour urinary free cortisol (UFC) — at least 2 collections, compared against the assay-specific upper limit of normal provided by the reporting laboratory.
• Late-night salivary cortisol — at least 2 measurements, compared against an assay-specific reference range.
• 1 mg overnight dexamethasone suppression test (DST), or the 2-day low-dose (0.5 mg every 6 hours for 48 hours) DST — a post-dexamethasone cortisol above 1.8 mcg/dL (50 nmol/L) is the standard abnormal threshold.

Discordant results should prompt repeating or adding a different first-line test, not immediately escalating to localization imaging. Also consider a pseudo-Cushing state — severe depression, alcohol use disorder, poorly controlled diabetes, severe obesity, and pregnancy can all produce a mildly abnormal screening result without true autonomous hypercortisolism; a dexamethasone-CRH test can help separate the two when the distinction is unclear.

Testing pitfalls

Oral estrogen raises cortisol-binding globulin and can falsely elevate total cortisol on the DST — discontinue for about 6 weeks before testing where feasible. Oral hydrocortisone and prednisone/prednisolone cross-react with most cortisol immunoassays and must be accounted for or temporarily bridged with dexamethasone before testing, since dexamethasone itself does not cross-react on most assays — the same property that makes chronic dexamethasone the highest HPA-suppression-risk oral agent (see Drug Tables) also makes it useful for bridging a patient through diagnostic testing.

Localizing confirmed endogenous disease

Once endogenous Cushing syndrome is confirmed, measure plasma ACTH:

• Suppressed or undetectable ACTH indicates ACTH-independent disease — proceed to adrenal CT to characterize a unilateral adenoma/carcinoma or bilateral hyperplasia.
• Normal-to-elevated ACTH indicates ACTH-dependent disease — proceed to pituitary MRI. A pituitary lesion 6 mm or larger with concordant biochemistry generally confirms Cushing's disease. If the MRI is negative or equivocal, or results are discordant, a high-dose DST, a CRH or desmopressin stimulation test, and inferior petrosal sinus sampling (IPSS) help distinguish a pituitary from an ectopic ACTH source before a body-imaging search for an occult ectopic tumor.^[2]

• Normalize tissue cortisol exposure — by removing or resecting the endogenous source, or by reducing exogenous glucocorticoid therapy to the lowest dose that still adequately controls the condition it was prescribed for.
• For iatrogenic disease specifically: taper safely toward physiologic replacement (or full discontinuation) without precipitating adrenal insufficiency, while addressing the original indication for the steroid by another means wherever possible (a genuine steroid-sparing strategy, not simply "less of the same drug").
• Reverse or prevent the systemic complications — hypertension, hyperglycemia, dyslipidemia, osteoporosis/fracture, hypercoagulability, myopathy, and infection risk from immunosuppression.
• Preserve or restore HPA axis function, recognizing that biochemical recovery lags weeks to months behind cortisol normalization and needs confirmation before a taper is fully stopped.
• For endogenous disease not cured by surgery: control cortisol medically without over-treating into iatrogenic adrenal insufficiency — the "block and replace" balance.
• Support psychological well-being throughout — both the physical changes of the syndrome itself and the mood effects of glucocorticoid excess or withdrawal.

• Steroid emergency card and medical alert identification for any patient actively tapering off, or recently discontinued from, chronic glucocorticoid therapy — identical to primary adrenal insufficiency — until HPA axis recovery is confirmed.^[1]
• An individualized, written tapering schedule the patient keeps and can follow themselves, since a safe taper can run for months and adherence commonly slips without one.
• Bone health — weight-bearing exercise, fall-risk reduction, and adequate calcium/vitamin D intake, alongside the pharmacologic bone protection covered in Monitoring & Follow-Up.
• Structured cardiovascular risk-factor management — home blood pressure monitoring and dietary counselling — given the added contribution of glucocorticoid excess to hypertension and dyslipidemia.
• Infection-prevention counselling for a patient on ongoing supraphysiologic glucocorticoid doses — a routine vaccination review (avoiding live vaccines during significant immunosuppression) and prompt reporting of any new fever, since classic inflammatory warning signs are blunted.
• Coordinated, multidisciplinary follow-up — endocrinology, the specialty that originally prescribed the causative corticosteroid (respirology, rheumatology, transplant medicine, dermatology, and others), and neurosurgery when a pituitary or adrenal tumor is identified.
• For confirmed endogenous disease: pre-operative counselling and post-operative expectation-setting, since transient glucocorticoid-withdrawal symptoms are expected even after a technically successful surgical cure, while the normal (previously suppressed) adrenal tissue recovers.

Pediatrics

Growth failure or a slowing growth velocity despite ongoing weight gain is the most specific pediatric clue to Cushing syndrome — in simple exogenous (non-glucocorticoid) obesity, height velocity is normal or increased, not reduced. Iatrogenic Cushing syndrome from high-dose or prolonged inhaled, intranasal, or topical corticosteroids is a particular pediatric concern given the added growth-suppression risk on top of adrenal suppression — use the lowest effective pediatric dose and step down as soon as disease control allows.^[4]

Older adults

Baseline osteoporosis/fracture risk and cardiovascular risk are already higher in this group, so glucocorticoid-attributable bone loss and hypertension are more consequential, not less — do not defer bone protection while "watching and waiting" in an older patient on chronic corticosteroids.^[3] Cognitive and mood effects of both hypercortisolism and glucocorticoid withdrawal can be harder to distinguish from other causes of delirium or dementia in this age group.

Hepatic and renal considerations

Ketoconazole and mitotane both carry meaningful hepatotoxicity risk and need baseline and periodic liver enzyme monitoring; avoid ketoconazole in significant pre-existing hepatic impairment. Mitotane accumulates in adipose tissue with a very long half-life and needs specialist-guided dosing regardless of renal function; other agents in this chapter do not require routine renal dose adjustment, but doses should still be reviewed individually.

Drug interactions

Ketoconazole, osilodrostat, and etomidate all carry QT-prolongation risk — review the full medication list for other QT-prolonging drugs before starting any of them. Ketoconazole is itself a potent CYP3A4 inhibitor and raises levels of many co-administered drugs, including some inhaled/intranasal corticosteroids — the same interaction mechanism responsible for the case illustrated in Recognize the Condition. More broadly, any strong CYP3A4 inhibitor (ritonavir and other boosted protease inhibitors, itraconazole, and some SSRIs) added to an existing corticosteroid is a well-documented precipitant of iatrogenic Cushing syndrome at an otherwise unremarkable steroid dose.^[4]

• Confirmed endogenous disease, post-treatment: cortisol/UFC per specialist protocol to confirm surgical remission, then periodically thereafter to screen for recurrence, since recurrence can occur years after an apparently successful cure.^[6]
• Iatrogenic disease, during and after a taper: track progress against the written taper schedule at every visit; check a morning cortisol or ACTH stimulation test as the dose approaches the physiologic range to judge HPA axis recovery before full discontinuation, and continue sick-day/emergency-injection education until recovery is confirmed.^[1]
• Any patient on medical therapy for endogenous disease (except mifepristone — see Common Errors): periodic UFC/cortisol to titrate dose and avoid over-treating into iatrogenic adrenal insufficiency.
• Bone: baseline DXA at diagnosis or at the start of chronic glucocorticoid therapy, with periodic follow-up per the ACR glucocorticoid-induced-osteoporosis guideline, and a fracture-risk assessment that explicitly accounts for glucocorticoid exposure rather than bone density alone.^[3]
• Cardiometabolic: blood pressure at every visit; fasting glucose/HbA1c and a lipid panel at baseline and periodically, more frequently during pasireotide therapy or a high-dose steroidogenesis inhibitor.
• Liver enzymes at baseline and periodically for a patient on ketoconazole or mitotane.
• Electrolytes (potassium) for a patient on metyrapone, osilodrostat, or mifepristone, given their mineralocorticoid-related effects.
• ECG/QTc at baseline and with dose changes for ketoconazole, osilodrostat, or etomidate, and whenever another QT-prolonging drug is added.
• Ongoing screening for infection, mood/psychiatric symptoms, and — in a patient with Cushing's disease treated by bilateral adrenalectomy — pituitary MRI surveillance for Nelson syndrome.

1. For apparent iatrogenic Cushing syndrome not improving despite a taper, reconfirm that every route of steroid exposure has genuinely been captured and reduced — including topical, inhaled, intranasal, and injected sources, plus any new interacting CYP3A4 inhibitor — before assuming the taper itself has failed.
2. For endogenous disease with persistent or recurrent hypercortisolism after surgery, confirm the original diagnosis and localization were correct (repeat biochemistry, re-image) before escalating therapy.
3. Optimize a single steroidogenesis inhibitor to its effective dose, guided by UFC/cortisol rather than symptoms alone, before concluding the drug class has failed.
4. For inadequate response to monotherapy, combine agents with different mechanisms — for example, a steroidogenesis inhibitor plus a pituitary-directed agent for Cushing's disease, or add mifepristone specifically to address refractory hyperglycemia.
5. Reassess candidacy for repeat surgery, radiotherapy (Cushing's disease), or resection of a newly localized ectopic ACTH source.
6. For severe, medically refractory hypercortisolism, discuss bilateral adrenalectomy — definitive, but it commits the patient to lifelong glucocorticoid and mineralocorticoid replacement and, in Cushing's disease, lifelong Nelson syndrome surveillance.
7. If control remains difficult after working through the steps above, refer to or consult a specialist endocrinology/pituitary centre rather than continuing to escalate therapy empirically.

• Stopping a chronic glucocorticoid abruptly for any reason, including running out of medication between refills or a patient self-discontinuing once they feel better.
• Ordering an endogenous Cushing syndrome workup without first taking a complete inventory of every corticosteroid-containing product the patient uses — an unrecognized exogenous source makes biochemical testing uninterpretable and the workup unnecessary.
• Missing a new drug interaction (a CYP3A4 inhibitor added to an existing corticosteroid) as the actual cause of new Cushingoid features, rather than assuming the steroid dose itself must have changed.
• Diagnosing Cushing syndrome from a single abnormal screening test without a second confirmatory test, or without considering a pseudo-Cushing state (depression, alcohol use disorder, poorly controlled diabetes, severe obesity).
• Using UFC or serum cortisol to titrate mifepristone — it blocks the glucocorticoid receptor rather than lowering cortisol, so cortisol levels do not fall and are not interpretable; dose only on the clinical picture.
• Not recognizing that a patient can have symptoms of adrenal insufficiency on mifepristone despite a normal or elevated cortisol level, because of receptor blockade rather than true cortisol deficiency.
• Assuming HPA axis recovery is complete as soon as the glucocorticoid dose reaches the physiologic range — recovery can lag weeks to months and needs confirmation before full discontinuation.
• Skipping bone-protective and cardiometabolic monitoring in a patient who "only" needs a short course of high-dose steroids, when such courses are often extended or renewed in practice.
• Missing the hypercoagulable state of Cushing syndrome (endogenous or exogenous) as a contributor to a new venous thromboembolism.
• Forgetting that dexamethasone does not cross-react on most cortisol immunoassays (useful for bridging testing) while hydrocortisone and prednisone/prednisolone do — using the wrong bridging agent invalidates the test.
• Treating iatrogenic Cushing syndrome as a reason to stop the causative steroid outright, rather than first addressing whether the condition it treats can be controlled another way.

How to use this table: Doses are adult doses and require patient-specific confirmation. Select any linked drug name to open its complete Pharmasist Drug Database page.

Corticosteroid formulations most associated with iatrogenic Cushing syndrome and HPA-axis suppression

Not a treatment table — a quick reference for the routes and formulations most often implicated, to support the exposure inventory in Assessment & Diagnosis and the tapering plan in Choose Initial Treatment. Risk scales with potency, dose, duration, and any interacting CYP3A4 inhibitor.

Steroidogenesis inhibitors (adrenal-directed medical therapy)

1st-line medical option for endogenous hypercortisolism not cured by surgery, or as a bridge before surgery.

Glucocorticoid receptor antagonist

Blocks the glucocorticoid receptor rather than lowering cortisol production — cortisol/UFC cannot be used to monitor or titrate this drug; dose only on the clinical picture.

Pituitary-directed medical therapy — Cushing's disease specifically

Targets the corticotroph tumor itself rather than blocking cortisol synthesis or action; reserved for Cushing's disease not cured by, or awaiting, pituitary surgery.

Emergency parenteral therapy — severe or life-threatening hypercortisolism

ICU-level therapy for florid, rapidly progressive hypercortisolism (severe psychosis, uncontrolled infection, severe hypokalemia/hypertension) where oral steroidogenesis inhibitors cannot act fast enough.

Physiologic glucocorticoid replacement — iatrogenic-Cushing tapering and HPA-axis recovery

Used once a chronic corticosteroid taper approaches the physiologic range, and for any patient with confirmed or presumed ongoing HPA-axis suppression — identical in principle to chronic replacement in primary adrenal insufficiency.