Key Points
- Confirm hypercortisolism before etiologic testing.
- Use at least one high-accuracy screening test; abnormal results typically require confirmatory testing.
- ACTH level differentiates pituitary/ectopic from adrenal disease.
- Transsphenoidal surgery is first line for Cushing disease.
- Monitor closely for postoperative adrenal insufficiency.
Algorithm
- Clinical suspicion based on phenotype and comorbidities.
- Exclude exogenous glucocorticoid exposure.
- Screening test: late-night salivary cortisol, 1-mg DST, or 24-h UFC.
- Confirm abnormal results; rule out pseudo-Cushing states.
- Measure plasma ACTH.
- ACTH low → adrenal CT; ACTH normal/high → pituitary MRI.
- If MRI non-diagnostic → inferior petrosal sinus sampling.
- Treat source → surgery first line → adjunct medication if required.
- Long-term follow-up for metabolic, cardiovascular, and bone complications.
Clinical Synopsis & Reasoning
Cushing’s syndrome results from chronic glucocorticoid excess and presents with progressive central obesity, facial fullness, dorsocervical fat pad, easy bruising, thin skin, wide violaceous striae, proximal muscle weakness, mood changes, hypertension, impaired glucose tolerance, and increased infection risk. A detailed review of medication use is essential because exogenous glucocorticoids are the most common cause. Endogenous causes arise from ACTH-dependent (pituitary adenoma, ectopic ACTH) or ACTH-independent (adrenal adenoma/carcinoma, bilateral adrenal hyperplasia) sources. Because pseudo-Cushing states (alcohol use disorder, severe stress, major depression, uncontrolled diabetes) can mimic the phenotype, biochemical confirmation is necessary before imaging.
Diagnostic Strategy
Screening requires at least one high-accuracy first-line test: (1) late-night salivary cortisol (two measurements), (2) 1-mg overnight dexamethasone suppression test, or (3) 24-hour urinary free cortisol (two measurements). Abnormal results warrant repetition or confirmation using a second modality. Once hypercortisolism is established, measure plasma ACTH to guide localization. Low or suppressed ACTH suggests adrenal origin; obtain adrenal CT. Normal or high ACTH suggests a pituitary or ectopic source; obtain pituitary MRI. If MRI is inconclusive, inferior petrosal sinus sampling distinguishes pituitary from ectopic secretion.
Treatment Strategy & Disposition
First-line treatment for endogenous Cushing’s syndrome is surgical resection of the underlying lesion—transsphenoidal surgery for Cushing disease, adrenalectomy for adrenal tumors, and tumor-directed therapy for ectopic ACTH production. Medical therapy (ketoconazole, metyrapone, osilodrostat, mifepristone, or pasireotide) is used for preoperative control, postoperative recurrence, or when surgery is contraindicated. Monitor for adrenal insufficiency after treatment. Long-term management includes cardiometabolic risk reduction, bone health monitoring, infection prevention, and psychiatric support.
Epidemiology / Risk Factors
- Cushing disease is the most common endogenous cause (~60–70%).
- ACTH-independent adrenal causes include adenomas, carcinomas, and bilateral hyperplasia.
- Women affected more often than men.
Investigations
| Test | Role / Rationale | Typical Findings | Notes |
|---|---|---|---|
| Late-night salivary cortisol | High-sensitivity screening | Elevated in Cushing syndrome | Repeat twice due to variability |
| 1-mg dexamethasone suppression test | Loss of cortisol suppression | AM cortisol >1.8 µg/dL | Be cautious with medications affecting dex metabolism |
| 24-hour urinary free cortisol | Integrates daily cortisol production | Elevated | Obtain two samples |
| Plasma ACTH | Differentiate ACTH-dependent vs independent | Low in adrenal tumors; high/normal in ACTH-dependent | Key branching point |
| Pituitary MRI | Identify pituitary adenoma | Microadenoma or normal | Normal MRI does not exclude Cushing disease |
| Adrenal CT | Identify adrenal tumor or hyperplasia | Adenoma, carcinoma, or nodular hyperplasia | Low ACTH indicates adrenal imaging |
| Inferior petrosal sinus sampling | Differentiate pituitary vs ectopic ACTH | Central-to-peripheral ACTH gradient | Gold standard when MRI is non-localizing |
Pharmacology
| Medication | Mechanism | Onset | Role in Therapy | Limitations |
|---|---|---|---|---|
| Ketoconazole | Inhibits adrenal steroidogenesis | Days–weeks | Medical control of hypercortisolism | Hepatotoxicity; drug interactions |
| Metyrapone | Blocks 11β-hydroxylase | Hours–days | Rapid cortisol reduction | Androgenic side effects; hypertension |
| Osilodrostat | Potent 11β-hydroxylase inhibitor | Hours–days | Effective for persistent or recurrent disease | Risk of AI, requires close titration |
| Pasireotide | Somatostatin analog reducing ACTH | Weeks | Alternative for Cushing disease when surgery fails | Hyperglycemia common |
| Mifepristone | Glucocorticoid receptor antagonist | Rapid | Useful for diabetes/prediabetes with hypercortisolism | Cortisol cannot be used to monitor response |
Prognosis / Complications
- Untreated hypercortisolism carries high mortality from cardiovascular, thrombotic, and infectious complications.
- Surgical remission improves survival but long-term comorbidity risk persists.
- Psychiatric and metabolic recovery may take months to years.
Patient Education / Counseling
- Explain diagnostic steps and need for confirmation before imaging.
- Discuss surgical expectations, risks, and the possibility of postoperative adrenal insufficiency.
- Emphasize importance of long-term cardiometabolic monitoring.
- Provide support for mental health symptoms, fatigue, and recovery timeline.
References
- Nieman LK et al. The Diagnosis of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline (2008). — Link
- Fleseriu M et al. Treatment of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline (2015). — Link
- Newell-Price J et al. The diagnosis and differential diagnosis of Cushing's syndrome. Endocr Rev. 1998;19(5):647–672. — Link
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