Cushing syndrome is a clinical metabolic disorder characterized by disrupted glucose, protein, and lipid metabolism induced by excessive endogenous cortisol secretion or long-term exogenous glucocorticoid intake. Obesity is the most typical and prominent manifestation of Cushing syndrome, which differs significantly from simple obesity in clinical phenotype, pathogenesis, and prognosis.

1. Core Concept and Classification of Cushing Syndrome

1.1 Definition and Epidemiological Characteristics

Cushing syndrome refers to a series of clinical syndromes caused by chronic hypercortisolism, either from over-secretion of endogenous cortisol or long-term high-dose exogenous glucocorticoid administration. According to the Chinese Guidelines for the Diagnosis and Treatment of Endocrine and Metabolic Diseases (2024), the annual incidence in China is approximately 2–3 per million population, with a 3–5 times higher prevalence in females than males, predominantly affecting individuals aged 20–50 years. Endogenous Cushing syndrome accounts for 80% of all cases, among which 70% are caused by pituitary adrenocorticotropic hormone (ACTH)-secreting adenomas (Cushing disease), 15%–20% by ectopic ACTH syndrome, and 10% by autonomous adrenal tumors.

1.2 Etiological Classification and Pathogenic Mechanisms

1.2.1 ACTH-Dependent Cushing Syndrome (75%)

Cushing disease: Caused by pituitary microadenomas (< 1 cm) that autonomously secrete excessive ACTH, accounting for 70% of endogenous cases with a female predominance (female:male = 4:1). Serum ACTH is moderately elevated (200–500 pg/mL), leading to bilateral adrenal cortical hyperplasia (Peking Union Medical College Hospital, 2025).

Ectopic ACTH syndrome: Non-pituitary tumors (e.g., thymic carcinoma, lung cancer) aberrantly secrete ACTH, accounting for 15%–20% of cases. Serum ACTH increases significantly (> 500 pg/mL) with rapid disease progression; 60% of patients develop severe hypokalemia (< 3.0 mmol/L) within 3 months.

1.2.2 ACTH-Independent Cushing Syndrome (25%)

Adrenal adenoma/carcinoma: Benign unilateral adrenal adenomas account for 10% and malignant adrenal carcinomas for 5% of cases. Tumors autonomously secrete cortisol, resulting in suppressed serum ACTH (< 10 pg/mL), and abdominal CT detects unilateral adrenal space-occupying lesions (2–5 cm in diameter).

Nodular adrenal hyperplasia: A rare subtype (5%), including primary pigmented nodular adrenocortical disease (PPNAD), which is frequently associated with Carney complex (Ruijin Hospital, 2024).

1.2.3 Exogenous Cushing Syndrome

Long-term administration of glucocorticoids (e.g., prednisone > 10 mg/d for more than 2 weeks) accounts for 20% of all cases. Patients present with typical central obesity without adrenal hyperplasia, and serum ACTH is profoundly suppressed (< 5 pg/mL).

2. Pathophysiological Mechanisms of Metabolic Disorders

2.1 Core Mechanism of Glucose Metabolism Disorder

Excess cortisol induces hyperglycemia through two primary pathways:

Enhanced hepatic gluconeogenesis: Cortisol activates phosphoenolpyruvate carboxykinase, increasing hepatic glucose output by 30%–50%. The incidence of fasting blood glucose ≥ 7.0 mmol/L reaches 60% (Chinese Journal of Endocrinology and Metabolism, 2025).

Peripheral insulin resistance: Cortisol inhibits glucose uptake and utilization in muscle and adipose tissues. 75% of patients present with HOMA-IR > 2.5, and 25% progress to pituitary-dependent diabetes mellitus.

2.2 Molecular Basis of Abnormal Fat Distribution

Cortisol induces adipose tissue remodeling and abnormal fat redistribution, which is the fundamental cause of Cushing-related obesity:

Central obesity formation: Cortisol promotes proliferation of omental adipocytes and inhibits lipase activity, resulting in preferential abdominal fat accumulation. Patients develop characteristic "moon face", "buffalo hump", and increased waist-to-hip ratio (> 0.9 in females, > 1.0 in males), with an incidence rate of 85%.

Peripheral muscle and fat loss: Excess cortisol accelerates skeletal muscle protein catabolism, increasing serum creatine kinase (CK) levels 2–3 times and reducing limb muscle mass by 20% compared with healthy individuals (China Obesity Prevention and Control Blue Book, 2024). This leads to the typical paradoxical presentation of central obesity combined with thin extremities.

2.3 Cardiovascular Damage Mechanisms

Chronic hypercortisolism causes multiple cardiovascular complications: hypertension occurs in 80% of patients due to sodium and water retention and increased angiotensin Ⅱ sensitivity, with systolic blood pressure commonly ranging from 150–180 mmHg. Dyslipidemia is characterized by elevated LDL-C (> 3.4 mmol/L) and decreased HDL-C (< 1.0 mmol/L), increasing coronary heart disease risk by 2.8-fold (HR=2.8, 95% CI: 2.1–3.7).

3. Clinical Manifestations of Cushing Syndrome

3.1 Typical Systemic Symptoms and Signs

3.1.1 Core Metabolic Manifestations

Abnormal weight gain:90% of patients experience significant weight gain (average 15–20 kg), characterized by trunk fat accumulation and relatively thin limbs, which is pathognomonic for Cushing obesity and differentiates it from simple generalized obesity.

Skin lesions: 60% of patients develop wide purple striae (> 1 cm) on the abdomen and inner thighs; 30% present with acne and hirsutism; 20% of Cushing disease patients develop skin pigmentation due to concomitant ACTH elevation.

3.1.2 Endocrine and Reproductive Dysfunction

Female patients: 75% suffer from menstrual disorders (oligomenorrhea or amenorrhea), 50% have infertility, and 20% present with polycystic ovarian morphology on pelvic ultrasound.

Male patients: 60% have decreased libido, 30% develop erectile dysfunction, and 15% present with gynecomastia secondary to mild hyperprolactinemia.

3.1.3 Musculoskeletal Damage

Osteoporosis: Cortisol inhibits osteoblast activity; 65% of patients have lumbar spine T-score < −2.5, with a 4-fold increased fracture risk, predominantly vertebral compression fractures.

Proximal myopathy: 50% of patients present with proximal muscle weakness (difficulty climbing stairs), with grip strength reduced by 30% due to enhanced protein catabolism.

3.2 Special Manifestations in Children and Adolescents

Growth retardation: 80% of prepubertal patients have height below the 3rd percentile and advanced bone age of 2–3 years, with premature epiphyseal closure causing permanent adult height loss.

Precocious puberty: 70% of affected children are girls, presenting with premature breast development and menarche before 10 years old, secondary to cortisol-mediated growth hormone suppression.

3.3 Severe Complications and Warning Signs

Increased infection risk: Hypercortisolism suppresses immune function, increasing the incidence of pneumonia and urinary tract infections 3-fold; fungal infections (e.g., candidiasis) occur in 15% of patients.

Neuropsychiatric symptoms: 50% of patients develop anxiety and depression, and 10% progress to mania or psychosis, caused by overactivation of limbic glucocorticoid receptors.

4. Standardized Diagnostic System for Cushing Syndrome

4.1 Initial Clinical Screening Tests

4.1.1 24-Hour Urinary Free Cortisol (UFC)

The gold standard screening test with 95% sensitivity and 85% specificity. Normal reference value < 100 μg/24h; Cushing syndrome is strongly suspected when levels persistently exceed 200 μg/24h, requiring at least two consecutive valid tests (Chinese Expert Consensus on the Diagnosis of Cushing Syndrome, 2024).

4.1.2 Late-Night Salivary Cortisol

A non-invasive and convenient outpatient screening indicator. A cutoff value > 145 nmol/L at 23:00 indicates abnormal cortisol rhythm, with a diagnostic sensitivity of 92% (Endocrine Practice Guidelines, 2025).

4.2 Confirmatory Tests for Excluding Pseudo-Cushing State

4.2.1 Low-Dose Dexamethasone Suppression Test

Oral dexamethasone 0.5 mg every 6 hours for 48 hours. Morning serum cortisol > 50 nmol/L on day 3 confirms autonomous cortisol hypersecretion, with a diagnostic specificity of 90%.

4.2.2 Cortisol Diurnal Rhythm Detection

Physiologically, cortisol peaks at 8:00 a.m. (165–441 nmol/L), decreases to 50% of the peak at 4:00 p.m., and drops below 60 nmol/L at midnight. Over 80% of Cushing syndrome patients present with completely abolished diurnal rhythm and midnight cortisol > 100 nmol/L.

4.3 Etiological Localization Tests

4.3.1 Serum ACTH Assay

Cushing disease: ACTH 100–500 pg/mL, suppressible by more than 50% in the high-dose dexamethasone suppression test.

Ectopic ACTH syndrome: ACTH > 500 pg/mL, no response to high-dose dexamethasone suppression.

Adrenal-derived Cushing syndrome: ACTH < 10 pg/mL, with definite adrenal space-occupying lesions on CT/MRI.

4.3.2 Imaging Localization

Pituitary MRI: 1.5 mm thin-slice enhanced scanning detects pituitary microadenomas (3–10 mm) with 85% sensitivity; 70% of Cushing disease patients present with pituitary stalk deviation.

Adrenal CT: Plain and enhanced scanning shows round low-density lesions (< 10 HU) for benign adenomas and lobulated enhanced masses for adrenal carcinomas (Beijing Tiantan Hospital, 2024).

5. Standardized Treatment Strategies for Cushing Syndrome

5.1 First-Line Treatment for Cushing Disease: Transsphenoidal Pituitary Adenomectomy

5.1.1 Surgical Indications and Timing

Indicated for patients with pituitary microadenomas (< 1 cm) and drug intolerance or treatment failure, with a postoperative remission rate of 70%–85% (Chinese Journal of Neurosurgery, 2025). Surgical intervention within 6 months after diagnosis is recommended; the remission rate decreases to 60% and complication risk doubles when the disease course exceeds 2 years.

5.1.2 Perioperative Management

Preoperative preparation: Control hypertension below 140/90 mmHg with ACEI/ARB agents; implement intensive insulin therapy for preoperative blood glucose > 11.1 mmol/L.

Postoperative monitoring: Daily serum cortisol testing is mandatory. Cortisol < 50 nmol/L within 3 postoperative days indicates successful remission. 10% of patients develop temporary adrenal insufficiency requiring short-term hydrocortisone replacement (20–30 mg/d).

5.2 Ectopic ACTH Syndrome: Primary Tumor Resection Priority

Surgical resection of primary tumors (lung cancer, thymoma) is the core treatment, with cortisol levels normalizing within 2 weeks postoperatively and a 5-year survival rate of 30%–50% depending on tumor malignancy. For unresectable lesions, mitotane is initiated at 1 g/d and titrated to 2–6 g/d, controlling cortisol levels in 60% of patients with regular liver and renal function monitoring.

5.3 Adrenal-Derived Cushing Syndrome: Surgical Resection

Adrenal adenoma: Laparoscopic adrenalectomy is the standard procedure with a postoperative recurrence rate < 5% and lifelong cortisol surveillance.

Adrenal carcinoma: Open radical surgery combined with adjuvant mitotane therapy yields a 5-year survival rate of 40%, with most recurrences occurring within 2 postoperative years (Zhongshan Hospital, 2024).

5.4 Pharmacotherapy: Adjuvant and Alternative Regimens

5.4.1 Cortisol Synthesis Inhibitors

Ketoconazole: Inhibits 11β-hydroxylase, initiated at 200 mg twice daily, normalizing cortisol in 80% of patients with a 15% incidence of elevated transaminases.

Pasireotide: Targets somatostatin receptors, applicable for recurrent Cushing disease with an efficacy rate of 65% and a 30% risk of secondary hyperglycemia.

5.4.2 Symptomatic Treatment for Complications

Osteoporosis: Annual zoledronic acid 5 mg combined with calcium 1000 mg/d and vitamin D 800 IU/d increases lumbar bone density by 2%–3% yearly.

Hypertension: Spironolactone 20–40 mg twice daily antagonizes mineralocorticoid effects of cortisol, achieving a 70% blood pressure control rate.

6. Postoperative Management and Long-Term Follow-Up

6.1 Early Postoperative Complication Management

6.1.1 Adrenal Insufficiency

Occurring in 30% of Cushing disease patients postoperatively, presenting with fatigue, nausea, and hypotension. Emergency intravenous hydrocortisone 100 mg every 8 hours is administered for cortisol < 100 nmol/L, followed by gradual tapering to physiological doses (20–30 mg/d). Hormone withdrawal is feasible when morning cortisol > 165 nmol/L and ACTH > 10 pg/mL at 6–12 months postoperatively.

6.1.2 Electrolyte Disorders

Hypokalemia occurs in 40% of patients after ectopic ACTH tumor resection. Potassium supplementation maintains serum potassium at 4.0–4.5 mmol/L; severe hypokalemia (< 3.0 mmol/L) requires intravenous potassium chloride 60 mmol/d with continuous ECG QT interval monitoring.

6.2 Long-Term Surveillance Key Points

6.2.1 Imaging Follow-Up

Cushing disease patients undergo pituitary MRI at 6 months, 1 year, and 2 years postoperatively, followed by annual screening. The 5-year recurrence rate is 10%–15%. Adrenal surgery patients receive annual adrenal CT, with a 30% risk of contralateral adrenal atrophy requiring stress hormone replacement.

6.2.2 Metabolic Index Monitoring

Blood glucose and lipids are tested quarterly postoperatively; diabetic patients receive lifelong follow-up with HbA1c target < 7.0%. Annual lumbar and femoral neck bone density detection continues until T-score > −2.0.

6.3 Lifestyle Modification

Patients adhere to a low-salt (< 5 g/d), high-protein (1.2–1.5 g/kg/d), high-calcium (1200 mg/d) diet with restricted high-sugar and high-fat intake. 150 minutes of weekly moderate aerobic exercise improves insulin resistance and reduces cardiovascular risk by 30%. Semi-annual HADS psychological assessment is recommended, with CBT or SSRI intervention for scores ≥ 8 (25% postoperative anxiety-depression incidence).

7. Prognosis and Risk Factors of Cushing Syndrome

7.1 Prognostic Differences by Etiology

7.2 Recurrence Risk Factors

For Cushing disease, microadenomas > 8 mm and postoperative residual enhanced lesions increase the recurrence rate to 25% with mandatory long-term ACTH and cortisol monitoring. For adrenal carcinoma, tumors > 6 cm and Ki-67 index > 10% confer a 60% recurrence rate requiring quarterly postoperative CT surveillance.

7.3 Overall Survival Analysis

The overall 5-year survival rate is 90% for Cushing disease, 50% for ectopic ACTH syndrome, and 40% for adrenal carcinoma (Journal of Clinical Endocrinology, 2025). Early diagnosis (disease course < 1 year) and stable cortisol control (165–441 nmol/L at 8:00 a.m.) improve long-term survival by 40%.

8. Hereditary and Special Subtypes of Cushing Syndrome

8.1 Familial Cushing Syndrome

Accounting for < 5% of all cases, mainly including Carney complex (autosomal dominant inheritance, 90% PRKAR1A gene mutation, complicated with cutaneous and cardiac myxomas) and familial ectopic ACTH syndrome (associated with APC and MEN1 gene mutations), requiring familial genetic screening.

8.2 Cushing Syndrome in Pregnancy

Physiological cortisol elevation during pregnancy increases diagnostic difficulty. Abnormal thresholds are defined as salivary cortisol > 200 nmol/L and 24-hour UFC > 300 μg/24h. Surgical resection is feasible in the second trimester with a 50% increased hydrocortisone replacement dose to meet gestational physiological demands.

Frequently Asked Questions about Cushing Syndrome

Q1: Is Cushing syndrome a severe disease?

Disease severity depends on etiology and treatment timing. Early diagnosed and standardized treated patients achieve favorable prognosis. Long-term untreated hypercortisolism causes irreversible cardiovascular lesions, osteoporosis, diabetes, and immune deficiency, significantly increasing mortality and disability risks.

Q2: Can Cushing syndrome be completely cured?

Most cases are curable. Surgical remission rates reach 70%–85% for Cushing disease and over 90% for adrenal adenomas. Ectopic ACTH syndrome and adrenal carcinoma have relatively poor prognosis, but active primary disease treatment and symptomatic management can significantly improve quality of life.

Q3: Is surgical treatment mandatory for Cushing syndrome?

Treatment regimens are etiology-dependent. Pituitary and adrenal tumor-induced Cushing syndrome prioritize surgical resection with medication as adjuvant or salvage therapy. Exogenous Cushing syndrome requires gradual glucocorticoid tapering instead of surgery, with individualized multidisciplinary evaluation required for all patients.

Q4: What are the typical symptoms of Cushing syndrome?

Core manifestations include characteristic central obesity, purple abdominal skin striae, hypertension, hyperglycemia, osteoporosis, and proximal muscle weakness. Pediatric patients present with growth retardation and precocious puberty; female patients have hirsutism, acne, and menstrual disorders; male patients suffer from decreased sexual function.