What is the recommended diagnostic and therapeutic approach to hypercortisolism (Cushing syndrome)?

Approach to Hypercortisolism (Cushing Syndrome)

Surgery is the definitive first-line treatment for all forms of Cushing syndrome—transsphenoidal selective adenomectomy by an experienced pituitary surgeon for Cushing's disease, unilateral adrenalectomy for adrenal adenomas, and resection with node dissection for ectopic ACTH-secreting tumors 1.

Initial Diagnostic Confirmation

Before pursuing any treatment, you must confirm true hypercortisolism using first-line screening tests:

• 24-hour urinary free cortisol (UFC) - multiple collections needed
• 1 mg overnight dexamethasone suppression test - failure to suppress cortisol below 1.8 μg/dL indicates hypercortisolism
• Late-night salivary cortisol - elevated levels confirm loss of circadian rhythm

Critical pitfall: Exclude exogenous steroid use first—this is the most common cause of Cushingoid features in clinical practice 2, 3.

Etiologic Differentiation

Once hypercortisolism is confirmed, measure plasma ACTH to distinguish:

ACTH-Dependent (ACTH normal or elevated)

• Cushing's disease (pituitary adenoma) - 70% of cases
• Ectopic ACTH secretion - 10-15% of cases

Proceed with:

• Pituitary MRI
• Bilateral inferior petrosal sinus sampling (IPSS) - the gold standard for differentiating pituitary from ectopic sources, recommended for all ACTH-dependent cases except clear pituitary macroadenomas 2, 3
• CRH stimulation test
• High-dose dexamethasone suppression test
• CT chest/abdomen if ectopic source suspected

ACTH-Independent (ACTH suppressed)

• Adrenal adenoma
• Adrenal carcinoma
• Bilateral adrenal disease

Proceed with adrenal CT or MRI for localization 1.

Surgical Management Algorithm

For Cushing's Disease

Transsphenoidal selective adenomectomy (TSS) by an experienced pituitary surgeon is the optimal treatment 1.

Postoperative monitoring essentials:

• Measure serum sodium multiple times during days 5-14 post-surgery to detect delayed hyponatremia 1
• Check free T4 and prolactin within 1-2 weeks to assess for hypopituitarism 1
• Obtain pituitary MRI within 1-3 months after successful surgery 1
• Measure postoperative serum cortisol to categorize as hypocortisolism (remission), eucortisolism, or persistent hypercortisolism 1

For Adrenal Disease

• Unilateral adrenalectomy for benign unilateral adenomas 1
• Bilateral adrenalectomy for bilateral disease 1

For Ectopic ACTH

• Localize and resect the tumor with appropriate node dissection 1
• If occult or metastatic, consider bilateral adrenalectomy as definitive treatment 1

Medical Therapy: When and How

Medical therapy is indicated in specific scenarios, not as first-line treatment 4, 1:

Indications for Medical Treatment

1. Severe hypercortisolism - presurgical preparation to reduce perioperative risk
2. Persistent disease after failed surgery
3. Recurrent disease after initial remission
4. Bridge therapy while awaiting radiation effects (takes 6-12 months)
5. Non-surgical candidates or when surgery declined
6. Occult or metastatic ectopic ACTH when source cannot be localized

Medical Therapy Selection by Clinical Scenario

For severe disease requiring rapid control 4:

• Osilodrostat or metyrapone - response within hours
• Ketoconazole - response within days
• Etomidate - for hospitalized patients unable to take oral medications
• Consider combination therapy with multiple steroidogenesis inhibitors if monotherapy insufficient
• Bilateral adrenalectomy if medical therapy fails in life-threatening cases

For mild disease with no visible tumor 4:

• First-line: Ketoconazole, osilodrostat, or metyrapone
• Alternative: Cabergoline (slower onset, less effective, but convenient dosing)

For mild-to-moderate disease with residual tumor 4:

• Prefer cabergoline or pasireotide for potential tumor shrinkage
• Critical caveat: Pasireotide causes hyperglycemia in high percentage of patients—careful patient selection essential

For patients with diabetes or glucose intolerance 1:

• Consider mifepristone (glucocorticoid receptor antagonist) - specifically improves hyperglycemia and weight gain
• Major limitation: Cannot monitor cortisol levels reliably, high risk of adrenal insufficiency, worsens hypokalemia
• Should only be used by clinicians with extensive Cushing's disease experience 4

Monitoring Medical Therapy

Use multiple serial measurements of both UFC and late-night salivary cortisol to assess treatment response 4. The goal is normalization of cortisol levels (or cortisol action with mifepristone).

Two approaches exist 5, 6:

1. Titration approach - gradually increase dose to normalize cortisol (preferred for mild disease)
2. Block-and-replace approach - induce adrenal insufficiency with high doses, then add glucocorticoid replacement (preferred for severe disease)

Management After Failed Surgery

When TSS fails or disease recurs, use shared decision-making among these options 1:

• Repeat transsphenoidal surgery - especially if incomplete resection or visible lesion on imaging
• Radiation therapy or radiosurgery - but confirm medical therapy controls cortisol first, as radiation takes 6-12 months to work
• Medical therapy with steroidogenesis inhibitors
• Bilateral adrenalectomy - definitive but requires lifelong glucocorticoid and mineralocorticoid replacement

Essential monitoring after bilateral adrenalectomy: Regular pituitary MRIs and ACTH levels to detect Nelson's syndrome (corticotroph tumor progression) 1.

Perioperative and Long-term Management

Perioperative Considerations

• Venous thromboembolism prophylaxis for all surgical patients 1
• Evaluate and treat risk factors for thrombosis preoperatively 1
• Offer age-appropriate vaccinations (influenza, Herpes zoster, pneumococcal) due to increased infection risk 1

Post-Remission Care

If postoperative hypocortisolism develops (indicating remission):

• Provide glucocorticoid replacement and patient education about adrenal insufficiency 1
• Perform morning cortisol and/or ACTH stimulation tests to assess HPA axis recovery 1
• Discontinue glucocorticoid when testing normalizes 1
• Re-evaluate other pituitary hormone deficiencies 1

Lifelong Surveillance

• Screen for recurrence throughout life using UFC or late-night cortisol at 6-12 month intervals 1
• Treat comorbidities aggressively: cardiovascular risk factors, osteoporosis, psychiatric symptoms, diabetes, hypertension 1
• These complications persist even after biochemical cure and require ongoing management

Special Populations

Pregnancy: Metyrapone may be considered with precautions; use higher cortisol targets (1.5 × ULN) given physiologically elevated cortisol in pregnancy 4.

Young women desiring pregnancy: Cabergoline may be preferred, but avoid in patients with bipolar disorder or impulse control disorders 4.

Bilateral macronodular adrenal hyperplasia (BMAH): Consider medical therapy to block aberrant hormone receptors as alternative to surgery 1.