Cushing Syndrome MCQ — NEET PG Practice Question | NEETPGAI
Cushing Syndrome
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stethoscope Medicine
A 45-year-old woman presents with progressive weight gain, proximal muscle weakness, and easy bruising. On examination, she has moon facies, a dorsocervical fat pad, central obesity with thin extremities, and the finding marked **D** in the diagram. Laboratory investigations reveal elevated 24-hour urinary free cortisol (8× upper limit of normal) and failure to suppress cortisol on low-dose overnight dexamethasone suppression test. Plasma ACTH is 65 pg/mL (normal <5 pg/mL). Which of the following is the most likely underlying etiology of her Cushing syndrome?
A. Primary bilateral macronodular adrenal hyperplasia
B. Ectopic ACTH secretion from small cell lung cancer
C. ACTH-secreting pituitary microadenoma (Cushing disease)
D. Adrenocortical adenoma
Explanation
Why ACTH-secreting pituitary microadenoma (Cushing disease) is right
The clinical presentation of wide violaceous abdominal striae (D) along with moon facies, buffalo hump, central obesity with thin extremities, and proximal muscle weakness is classic for Cushing syndrome from chronic glucocorticoid excess. The elevated plasma ACTH (65 pg/mL) indicates ACTH-dependent disease, ruling out adrenal causes. Among ACTH-dependent etiologies, Cushing disease (pituitary ACTH-secreting adenoma) is the most common endogenous cause, accounting for ~70% of endogenous Cushing syndrome cases. The microadenoma is the typical pituitary pathology. The elevated urinary free cortisol and failure to suppress on low-dose dexamethasone confirm hypercortisolism. A high-dose dexamethasone suppression test would typically show >50% cortisol reduction in Cushing disease, distinguishing it from ectopic ACTH syndrome. [Harrison's 21e Ch 386; Endocrine Society Cushing Syndrome Guidelines 2008]
Why each distractor is wrong
Ectopic ACTH secretion from small cell lung cancer: While ectopic ACTH syndrome is ACTH-dependent and would present with elevated ACTH, it accounts for only ~20% of ACTH-dependent Cushing syndrome. Moreover, ectopic ACTH typically does NOT suppress cortisol on high-dose dexamethasone suppression test (unlike pituitary disease), and patients often present with severe hypokalemic metabolic alkalosis due to the mineralocorticoid effect of very high cortisol levels—not prominent in this case.
Adrenocortical adenoma: This is an ACTH-independent cause of Cushing syndrome. Plasma ACTH would be suppressed (<5 pg/mL), not elevated at 65 pg/mL. The elevated ACTH rules out primary adrenal pathology.
Primary bilateral macronodular adrenal hyperplasia: This is also ACTH-independent and would present with suppressed plasma ACTH. The elevated ACTH in this patient excludes this diagnosis.
High-YieldNEET PG
Wide violaceous striae (>1 cm, especially on abdomen) are a hallmark skin manifestation of Cushing syndrome from chronic glucocorticoid excess; elevated ACTH indicates ACTH-dependent disease, and Cushing disease (pituitary microadenoma) is the most common endogenous cause (~70% of endogenous cases).
Harrison's 21e Ch 386; Endocrine Society Cushing Syndrome Guidelines 2008
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