Cushing’s Syndrome – Comprehensive Study Notes (AFP 2024)

Epidemiology

• Cushing’s syndrome is a rare, multisystemic disease caused by chronic exposure to supraphysiologic cortisol levels. Prolonged hypercortisolism leads to significant multisystem morbidity and mortality and reduced quality of life.

• Endogenous Cushing’s syndrome epidemiology:

  • Estimated annual incidence: $2\text{ to }8\ \text{cases per million}$ in the United States. The true incidence is likely higher due to underdiagnosis of ectopic ACTH sources. (AFP 2024)

  • Global prevalence varies: $39\text{ to }79\ \text{cases per million}$.2,9,17

  • Pediatric incidence: $1\text{ to }1.5\ \text{cases per million per year}$; Cushing’s disease accounts for $75\%\text{ to }80\%$ of new pediatric cases.18-20; about $10\%$ of all new Cushing’s syndrome cases occur in children each year.18,20

• Sex distribution: females are affected $3\text{ to }4:1$ compared with males; ectopic ACTH syndrome affects sexes more evenly.2,9,10

• Age: median age around $41.4:\text{years}$.6,7

• Comorbidity associations that increase prevalence estimates (variable): hypertension, uncontrolled diabetes, early-onset osteoporosis (0.5%–9% across studies).2,4,7,12,21

• Key clinical implication: screening and diagnosis may be delayed due to insidious onset and symptom overlap with common conditions; all forms of exogenous glucocorticoid use must be excluded first. Exogenous glucocorticoids are the most common cause of Cushing’s syndrome.1,2,4,6-11

What’s New on This Topic

• In tertiary-center referrals, myopathy, metabolic syndrome, osteoporosis, adrenal incidentaloma, and multiple Cushing’s-specific symptoms increase diagnostic likelihood; obesity alone is not a strong predictor.4, ohw? (AFP 2024)

• Remission after transsphenoidal surgery is about $80\%$ for microadenomas and $60\%$ for macroadenomas when performed by an experienced surgeon. Recurrences: about half occur within $5:\text{years}$ post-surgery.270

Etiology and Classification

• Exogenous (iatrogenic) Cushing’s syndrome is caused by administration of glucocorticoids and is the most common form; must be ruled out.2,4,6-11

• Endogenous Cushing’s syndrome: divided into ACTH-dependent and ACTH-independent forms.

  • ACTH-dependent: $80\%\text{-}85\%$ of endogenous cases.

  • ACTH-independent: $15\%\text{-}20\%$ of endogenous cases.

• Within ACTH-dependent causes:

  • Cushing’s disease: pituitary adenoma secreting ACTH; accounts for $75\%\text{-}80\%$ of endogenous cases.2,7,10,11

  • Ectopic ACTH syndrome: ACTH produced by nonpituitary tumors (e.g., small cell carcinoma, pulmonary carcinoid, pancreatic/thymic NETs, gastrinoma, medullary thyroid cancer, pheochromocytoma); represents $15\%\text{-}20\%$ of endogenous cases.2,10

  • Ectopic CRH production (<1% of cases).2,10

• Within ACTH-independent causes:

  • Unilateral adrenal adenoma (≈90% of ACTH-independent cases).

  • Adrenocortical carcinoma; rarely, bilateral macronodular adrenal hyperplasia (BMH), primary pigmented nodular adrenocortical disease (PPNAD), McCune-Albright syndrome, or other adrenal etiologies.2,10

• Pseudo–Cushing’s syndrome: physiologic hypercortisolism due to alcohol use disorder, obesity, uncontrolled diabetes, psychiatric conditions, PCOS, etc.2,7,10

• Cyclic Cushing’s syndrome: fluctuating symptoms with alternating active/inactive phases.2,7,10

• Diagnostic takeaway: distinguish exogenous from endogenous; identify ACTH-dependent vs ACTH-independent sources to tailor treatment. Table 1 summarizes differential diagnoses.2,10

Diagnostic Approach (Overview)

• Goal: confirm hypercortisolism and determine etiology (ACTH-dependent vs ACTH-independent). First-line therapy is surgical removal of the cortisol source; lifelong post-treatment monitoring is required.1,2,7-10,14,15,25,27-33

• Screening and confirmation: rely on multiple tests due to variability in cortisol across tests and time of day. The Endocrine Society recommends screening with any of the following: 24-hour urinary free cortisol (UFC), late-night salivary cortisol (LNSC), and/or 1 mg dexamethasone suppression test (DST).1-4,7,8,10,14,15,21,27,28

  • Two different tests positive confirms hypercortisolism; two negative tests generally exclude; reassess with a different test if clinical suspicion remains high.1,2,7,8,10

  • DST is preferred initial test if adrenal tumor suspected or if night-shift/circadian disruption is present; adrenal disease typically yields lower salivary/urinary cortisol.1,7,10

  • UFC and LNSC require multiple samples due to intra-individual variation (2–3 samples often needed).1-3,7,8,10,14,27,28

  • LNSC test has high sensitivity and specificity; DST has high sensitivity and good specificity. A negative 1 mg DST strongly argues against Cushing’s.1-3,25,27,28

• After hypercortisolism is confirmed, measure ACTH to distinguish ACTH-dependent vs ACTH-independent etiologies.1,2,7-10,14,15,25,27-33

• ACTH-independent (low ACTH) workup:

  • Adrenal CT or MRI to identify unilateral or bilateral adrenal lesions.1,3,10,29-32

• ACTH-dependent (normal or high ACTH) workup:

  • Pituitary MRI to evaluate for Cushing’s disease (ACTH-dependent from pituitary source).2,8,9,30

  • If pituitary imaging is unrevealing or discordant with biochemical testing, perform whole-body CT with inferior petrosal sinus sampling (IPSS) or CRH/desmopressin testing to differentiate Cushing’s disease from ectopic ACTH syndrome. IPSS is the diagnostic standard for this differentiation, particularly for suspected microadenomas.2,8,9,30

  • If imaging detects an adenoma ≥6 mm, pituitary gradient assessment and targeted testing guide management. IPSS is particularly recommended for adenomas <6 mm; its use for 6–9 mm lesions is debatable.2,8,9,30

Table Snapshot: Key Diagnostic Clues (Signs, Symptoms, and Lab Clues)

• General clues of Cushing’s syndrome (clinical): exogenous steroid use, multiple unexplained progressive symptoms, symptoms not typical for age, pseudo-Cushing’s features, fluctuating symptoms, multiple physician visits, deteriorating relationships/work.

• Physical appearance: moon face, facial plethora, alopecia, acne, hirsutism; weight gain with central obesity; dorsocervical/ supraclavicular fat; buffalo hump; thin skin; wide purple striae (>1 cm).

• Cardiovascular/metabolic: hypertension (70–85%), dyslipidemia (70%), edema, increased risk of venous thromboembolism; obesity with possible hypocoupling of other risk factors.

• Neurocognitive/psychological: cognitive impairment, mood changes, irritability, depression, anxiety; potential hippocampal volume changes and decreased cognitive function in many cases (70–85%).

• Musculoskeletal: proximal muscle weakness/atrophy (60–82%), osteoporosis or fractures (40–70%).

• Immunologic: immunosuppression with increased infection risk.

• Endocrine/other: hyperglycemia/diabetes risk (45–70%); hyperlipidemia; menstrual irregularities; delayed puberty/hypogonadism in some patients; sleep disturbances.

• Visual or mass effects: headaches and potential visual field defects with macroadenomas (18%–78%).

• Special note: no single symptom confirms or excludes disease; a constellation of findings increases pretest probability. Table 2 consolidates these clues.2,4,7,8,10-13,21,23,26,28-31

Diagnostic Testing: Details and Interpretation

• First-line screening tests (Table 3):

  • 1-mg DST (DST): sensitivity $85\%\text{ to }90\%$; specificity $95\%\text{ to }99\%$. Administer 1 mg dexamethasone at 11 p.m. and measure cortisol next morning 8–9 a.m. Consider also measuring dexamethasone levels.1-4,7,8,10,14,15,21,27,28

  • 24-hour UFC: sensitivity $80\%\text{ to }98\%$; specificity $45\%\text{ to }98\%$. Collect urine for 24 hours (start after first void; finish next morning). Repeat 2–3 times due to variability in about half of patients.1-3,7,8,10,14,27,28

  • LNSC: sensitivity $92\%\text{ to }100\%$; specificity $93\%\text{ to }100\%$. Collect saliva at 11 p.m. (avoid tobacco, brushing teeth, mouthwash prior). Repeat 2–3 times.1-4,7,8,10,14,15,21,27,28

• False positives/negatives and caveats (Table 3): caffeine interactions, shifts in binding proteins, pregnancy, liver/kidney function, drugs affecting dexamethasone metabolism (CYP3A4 inhibitors/inducers), pseudo-Cushing’s syndrome, poor collection, ingestion and/or vaping influences, etc.

• Second-line tests (when needed): inferior petrosal sinus sampling (IPSS) and CRH/desmopressin testing to distinguish CD from ectopic ACTH syndrome. IPSS is invasive and typically done at specialized centers; CRH/desmopressin testing is less invasive but less definitive.2,8,9,30

• Additional notes: Hair cortisol and hair cortisone show ongoing research status but are not yet widely available (Table 3).2,3,7,8,10,14,15,21

Management: Treatment Goals and Strategy

• Multidisciplinary approach: Endocrine Society recommends referral to a specialized center after confirmation of hypercortisolism due to diagnostic complexity, symptom overlap, and need for lifelong monitoring.1,3,9,32

• Role of the primary care physician: early recognition of signs, ordering initial tests, ensuring timely referral, and coordinating follow-up and comorbidity management.

Surgical Therapy (Definitive Treatment)

• The definitive treatment for all forms of Cushing’s syndrome is surgery.1-3,7,8,10,33

• Pituitary-directed disease (Cushing’s disease): transsphenoidal surgery by an experienced pituitary surgeon yields remission rates of about $80\%$ for microadenomas and $60\%$ for macroadenomas.1-3,7,8,10,33

• Adrenal disease: for unilateral adrenal adenomas, minimally invasive laparoscopic adrenalectomy is preferred; for bilateral macronodular adrenal hyperplasia or primary pigmented nodular adrenocortical disease, bilateral adrenalectomy is preferred. Open adrenalectomy is used for adrenal carcinomas.1,3,10,33

• Postoperative glucocorticoids: necessary until the hypothalamic-pituitary-adrenal axis recovers.1,3,7,10,33

• Surgical challenges: accuracy of imaging, precise localization, and risk of recurrence require specialized centers.1,3,9,32

Medical Therapy (Second-Line or Adjunctive)

• Indications for medical therapy: when patient declines surgery, is not a surgical candidate, has persistent/recurrent disease after surgery, or requires pretreatment before curative surgery.1,3,9,10,34-39

• Drug classes (Table 4):

  • Steroidogenesis inhibitors (adrenal-directed): Ketoconazole, Metyrapone, Osilodrostat, Etomidate, Mitotane, Levo-ketoconazole (investigational). Dosing ranges and notable adverse effects provided (e.g., hepatotoxicity with ketoconazole, GI upset, QT prolongation).1,3,7,8,10,34-39

  • Pituitary-directed therapies: Pasireotide (Signifor) and Pasireotide LAR; Cabergoline; Mifepristone (glucocorticoid receptor antagonist). Adverse effects include hyperglycemia, gallstones, QT prolongation, endometrial changes, and drug interactions.1,3,7,8,10,11,34-39

• Practical considerations: limited long-term data on efficacy, variable response, adverse effects, and discontinuation rates; cost considerations.1,10,34-39

• Radiotherapy: used as adjuvant therapy for aggressive tumor growth or persistent/recurrent disease after transsphenoidal surgery.1-3,10,33

Lifestyle, Behavior, and Quality of Life

• Cushing’s syndrome markedly reduces quality of life; two or more postoperative comorbidities predict poorer QoL.40-44

• Cognitive and psychiatric issues: memory, executive function, anxiety, depression, and mood disturbances are common and can persist post-treatment.40-44

• Behavioral health and education: patient and family education, counseling, and treatment of cognitive/psychiatric conditions are essential for recovery.40-44

• Lifestyle interventions: diet, exercise, and weight management can improve self-image, energy, sleep, and functioning; retraining can aid workforce re-entry.40-44

Prognosis, Recurrence, and Long-Term Outlook

• Recurrence rates vary: $5\%\text{ to }35\%$ depending on etiology and treatment.1,10

• Timing of recurrence: about $1/2$ of recurrences occur within $5:\text{years}$ of surgery.1,10

• Mortality: not substantially improved after treatment; cardiovascular/cerebrovascular disease, diabetes, dyslipidemia, hypertension, infections, and venous thromboembolism are major causes of morbidity and mortality.1,3-7,10,44

• Growth and development: in children, disease affects growth and development.18

Post-Treatment Monitoring and Follow-Up

• Lifelong monitoring by a multidisciplinary team is required; monitoring should begin once the HPA axis is restored and continue annually thereafter.1-4,10,15,40-44

• Monitoring aims: detect recurrence, manage comorbidities, and optimize QoL; coordinated care across endocrinology, neurosurgery, oncology (if needed), radiology, and primary care.40-44

Practical Implications and Takeaways

• Always rule out exogenous glucocorticoids when evaluating suspected Cushing’s syndrome. Exogenous sources are a frequent and preventable cause.1,2,4,6-11

• Use a structured diagnostic pathway with dual testing to confirm hypercortisolism and to determine etiology (ACTH-dependent vs ACTH-independent).2,7-10,14,15,25,27-33

• Reserve IPSS for inconclusive imaging or when precise differentiation between CD and ectopic ACTH syndrome will change management. IPSS is the diagnostic gold standard for distinguishing CD from ectopic ACTH sources.2,8,9,30

• Transsphenoidal surgery by experienced pituitary surgeons yields the best remission rates; otherwise, recurrence risk remains and requires ongoing surveillance.1-3,7,8,10,33

• Medical therapy is a secondary option with notable limitations, adverse effects, and variable efficacy; generally used when surgery is not feasible or while awaiting radiotherapy or tumor control.1,3,7,8,10,34-39

• Radiotherapy serves as an adjunctive option for residual or aggressive disease after surgery.1-3,10,33

• Quality of life and psychosocial functioning are integral to management; comprehensive care includes mental health support and rehabilitative services as part of long-term follow-up.40-44

References (Key Guidelines and Reviews)

• Endocrine Society guidelines and consensus reviews on diagnosis and management of Cushing’s disease and Cushing’s syndrome.1-4,7-15,21,25,27-33,34-39,40-44

• Notable studies/guidelines cited in the AFP article: Lancet Diabetes Endocrinol 2021 (consensus on diagnosis/management of Cushing’s disease), J Clin Endocrinol Metab, JAMA, and others.1-4,7-15,21,27-33,34-39,40-44

• Important numbers to remember: incidence $2\text{ to }8$ per million; prevalence $39\text{ to }79$ per million; female-to-male ratio $3\text{ to }4:1$; remission after pituitary surgery: $80\%$ (microadenoma) and $60\%$ (macroadenoma).1-4,7-15,21,27-33

Quick Reference: Flow Diagram (Conceptual)

• Screen for hypercortisolism with at least two tests (DST, UFC, LNSC). If positive on two tests, confirm hypercortisolism and measure ACTH.

• If ACTH is low → pursue adrenal imaging (CT/MRI) for adrenal cause. If ACTH is normal/high → pituitary MRI; if imaging is inconclusive, pursue IPSS or CRH/desmopressin testing and whole-body imaging to differentiate CD from ectopic ACTH syndrome.6-9,30

• Upon localization, plan definitive surgery if feasible; consider medical therapy or radiotherapy as adjuncts for residual disease or when surgery isn’t feasible.1-3,7-10,33,34-39

Note: All mathematical expressions are presented in LaTeX, enclosed within double-dollar symbols as requested. Where space or context required, standard clinical abbreviations and terms have been preserved for clarity and exam-style study use.