Cushing Syndrome
Also written as ACTH.
Cushing syndrome produces central obesity, purple striae, proximal weakness, hypertension and hyperglycaemia, and cortisol that is not suppressed by dexamethasone.
CUSHING'S SYNDROME
- Definition: Chronic excess of cortisol, either exogenous or endogenous.
- Causes: - Exogenous steroids: Most common overall cause. Leads to bilateral adrenal atrophy. - Cushing's Disease: Pituitary ACTH adenoma (70% of endogenous cases). Leads to bilateral adrenal hyperplasia. - Ectopic ACTH: From tumours like sm
- Clinical features: Central obesity, moon face, buffalo hump, purple striae, proximal muscle weakness, hypertension, hyperglycaemia, osteoporosis, hirsutism, amenorrhoea, depression.
- Diagnosis: - Confirmation: 24-hour urinary free cortisol, 1mg overnight dexamethasone suppression test (cortisol not suppressed). - Find cause: Plasma ACTH level (↑ suggests ACTH-dependent; ↓ suggests adrenal cause). - Localisation: Pituita
- Morphology: - Pituitary adenoma: Small, basophilic corticotroph adenoma, ACTH positive on immunohistochemistry. - Adrenal adenoma: Yellow, well-circumscribed tumour composed of uniform clear cells. - Adrenal carcinoma: Large, necrotic, pleo
Read this in Endocrine & Renal Pathology — Must Know Notes
CUSHING'S SYNDROME
- Definition: Chronic excess cortisol — exogenous or endogenous.
- Clinical: Central obesity, moon face, buffalo hump, wide purple striae, proximal muscle weakness, hypertension, hyperglycaemia, osteoporosis, hirsutism, amenorrhoea, easy bruising, depression.
- Ectopic ACTH: Rapid onset, severe hypokalaemic alkalosis, hyperpigmentation — no classic cushingoid features (tumour grows too fast).
- Confirm hypercortisolism: 24h urinary free cortisol, 1mg dexamethasone suppression test (cortisol not suppressed = abnormal)
- Find cause: plasma ACTH (↑ = ACTH-dependent; ↓ = adrenal)
Read this in Endocrine & Renal Pathology
Cushing's Syndrome
- Q: What is the diagnosis?
- Q: Characteristic physical features?
- Buffalo hump (fat pad on upper back/neck)
- Thin arms and legs (muscle wasting)
- Purple stretch marks (striae) on abdomen
Read this in Pathology Spot Exam Revision: Lymphoma, Adenoma, Appendicitis, FISH
What our notes say
- Cushing syndrome produces central obesity, purple striae, proximal weakness, hypertension and hyperglycaemia, and cortisol that is not suppressed by dexamethasone. (Endocrinology and Gastroenterology Question Bank: 12 Clinical MCQs)
- *Small cell lung carcinoma is the classic cause of paraneoplastic SIADH (ectopic ADH secretion), as well as Cushing syndrome (ACTH) and Lambert-Eaton myasthenic syndrome.* (End Sem Cat: Respiratory Pathology: Emphysema, ARDS, Pneumoconiosis)
- Small cell lung cancer is the classic paraneoplastic source of ectopic ACTH, causing Cushing syndrome. (Chemical Pathology: Endocrine Cases, Pituitary & Thyroid Q&A)
- | Endocrine and metabolic | Hyperthyroidism, Cushing's syndrome, uraemia, B12 or folate deficiency | (Bipolar and Related Disorders)
- Associated disorders include Cushing syndrome and secondary diabetes mellitus (Aponeurosis — Histology Question Bank)
- Cushing's syndrome — excess cortisol promotes gluconeogenesis, antagonizes insulin, causing insulin resistance (Medical MCQs: Chemical Pathology & Haematology Exam Review)
Study material on Cushing Syndrome
- LECTURE 6: Pancreatic and Adrenal Hormones
- Endocrine & Renal Pathology
- Chemical Pathology Practice Examination
- Endocrine & Renal Pathology — Must Know Notes
- ENDOCRINE PATHOLOGY
- Medical Physiology Paper II MCQs
- Hypothalamic Hormones: Master Regulators of the Endocrine System
- Chemical Pathology MCQs: Clinical Chemistry, Endocrine & Renal
- Chemical Pathology MCQs
- Chemical pathology and Endocrine pathology
- Endocrine & Renal Pathology
- Endocrine & Renal Pathology
- CHEMICAL PATHOLOGY MCQs
- Chemical Path Mcqs
- Chemical Pathology
- Chemical Pathology MCQS
Practice questions on Cushing Syndrome
The classic triad of Cushing syndrome includes all EXCEPT
- Central obesity
- Hypertension
- Hypoglycemia
- Striae
Answer: C. Hypoglycemia does NOT occur; cortisol causes hyperglycemia by stimulating gluconeogenesis and inducing insulin resistance. ---
The best outpatient screening test for Cushing syndrome is
- Random serum cortisol
- 24-hour urinary free cortisol
- Overnight 1 mg dexamethasone suppression test
- Morning ACTH level
Answer: C. Overnight DST is simple, cheap, and highly sensitive; failure to suppress cortisol below 50 nmol/L is abnormal. ---
Which test is used to confirm Cushing's syndrome?
- Serum cortisol at 8 AM
- Low-dose dexamethasone suppression test
- Serum ACTH
- 24-hour urine free cortisol Correct
Answer: B. This test differentiates normal individuals (who suppress cortisol) from those with Cushing's syndrome (who fail to suppress). ---
A patient with a central lung mass develops Cushing syndrome with high urinary cortisol that fails high-dose dexamethasone suppression. Which tumour is most responsible?
- Squamous cell carcinoma producing ectopic PTH-related peptide
- Adenocarcinoma with bilateral adrenal metastases destroying cortical tissue
- Small cell carcinoma producing ectopic ACTH causing Cushing syndrome
- Large cell carcinoma with direct hypothalamic invasion altering cortisol feedback
Answer: C. SCLC produces ectopic ACTH causing Cushing syndrome that characteristically fails high-dose dexamethasone suppression — distinguishing it from pituitary-driven Cushing disease. ---
Ectopic ACTH production causing Cushing syndrome is most commonly associated with
- Breast carcinoma
- Small cell lung carcinoma
- Renal cell carcinoma
- Colon carcinoma
Answer: B. SCLC is the most common cause of ectopic ACTH syndrome. ---
The best screening test for Cushing syndrome is
- Random serum cortisol
- 24-hour urinary free cortisol or overnight 1 mg dexamethasone suppression test
- Morning ACTH
- Serum potassium
Answer: B. UFC and overnight DST are first-line screens; random cortisol has poor sensitivity due to pulsatility. ---