Endocrinology Flashcards

A 34-year-old woman presents with hypertension, hypokalemia, and suppressed plasma renin activity. Aldosterone-to-renin ratio is markedly elevated. CT abdomen shows bilateral adrenal hyperplasia. She undergoes adrenal vein sampling (AVS), which demonstrates a lateralization ratio of 1.8 (right:left). Which of the following is the most appropriate next step?

Answer: Treat with mineralocorticoid receptor antagonist (spironolactone) rather than surgery

A lateralization ratio of ≥4:1 (or ≥3:1 with cosyntropin stimulation) is generally required to confirm unilateral disease and proceed with adrenalectomy. A ratio of 1.8 is non-lateralizing, indicating bilateral hyperplasia rather than a unilateral adenoma. In bilateral adrenal hyperplasia causing primary aldosteronism, the treatment of choice is medical management with a mineralocorticoid receptor antagonist such as spironolactone or eplerenone, not surgery. Proceeding with adrenalectomy based on an inadequate lateralization ratio would likely result in surgical failure without biochemical cure.

A 58-year-old man with a history of medullary thyroid carcinoma (MTC) treated with total thyroidectomy 10 years ago presents with rising calcitonin levels (current: 850 pg/mL). Neck ultrasound, CT chest/abdomen, and bone scan are all negative. Which of the following is the most appropriate next step in evaluation?

Answer: Perform selective venous catheterization with calcitonin sampling to localize occult disease

In biochemically persistent or recurrent MTC with negative conventional imaging, selective venous catheterization with calcitonin gradient sampling is the next step to localize occult metastatic disease (typically hepatic micrometastases or lymph nodes). This technique can identify a hepatic or regional gradient pointing toward a specific site of disease. 68Ga-DOTATATE PET is used for somatostatin receptor-positive tumors (e.g., carcinoid, paraganglioma) and has limited utility in MTC. Vandetanib is reserved for progressive, symptomatic, or unresectable/metastatic MTC — not indicated without confirmed active disease. Empiric radiation is inappropriate without a defined target.

A 45-year-old woman is evaluated for amenorrhea and galactorrhea. MRI shows a 6 mm pituitary microadenoma. Prolactin level is 210 ng/mL. She is started on cabergoline. After 12 months, her prolactin normalizes and repeat MRI shows tumor resolution. She desires to discontinue cabergoline. Which of the following factors is most strongly associated with sustained remission after dopamine agonist withdrawal?

Answer: Normalization of prolactin for at least 2 years and radiological tumor disappearance

The Endocrine Society guidelines recommend that dopamine agonist withdrawal may be attempted after at least 2 years of therapy if prolactin has normalized and the tumor is no longer visible on MRI. Studies show that radiological disappearance of the adenoma and sustained normoprolactinemia for ≥2 years are the strongest predictors of durable remission after withdrawal. Approximately 21–31% of patients achieve lasting remission after cabergoline discontinuation under these criteria. The prolactin nadir during therapy and patient sex are not validated predictors of remission. The absence of side effects is clinically useful but not predictive of remission.

A 29-year-old man presents with polyuria (6 L/day), polydipsia, and a serum sodium of 148 mEq/L. A water deprivation test is performed: after 8 hours of water deprivation, urine osmolality plateaus at 195 mOsm/kg. After desmopressin (DDAVP) administration, urine osmolality rises to 620 mOsm/kg. Which diagnosis best explains these findings?

Answer: Central diabetes insipidus

The water deprivation test shows failure to concentrate urine adequately (plateau of 195 mOsm/kg, well below the normal >600–800 mOsm/kg), confirming diabetes insipidus. The robust response to exogenous DDAVP (rise from 195 to 620 mOsm/kg, representing >50% increase) indicates that the kidneys are capable of responding to ADH — distinguishing central from nephrogenic DI. In nephrogenic DI, the kidneys fail to respond to DDAVP. In primary polydipsia, baseline urine osmolality during deprivation typically rises above 300–400 mOsm/kg (though may be blunted by chronic medullary washout). This pattern is diagnostic of complete central DI.

A 52-year-old woman undergoing workup for hypertension is found to have a 3.2 cm right adrenal incidentaloma. Labs reveal: 24-hour urine metanephrines normal, aldosterone-to-renin ratio normal, low-dose dexamethasone suppression test (1 mg overnight) shows cortisol of 3.8 mcg/dL. Which of the following is the most accurate statement about her management?

Answer: She likely has mild autonomous cortisol secretion and should be evaluated for metabolic comorbidities and cardiovascular risk

A post-dexamethasone cortisol of 1.8–5.0 mcg/dL (using the 1 mg overnight DST) defines 'possible autonomous cortisol secretion' (formerly called 'subclinical Cushing's syndrome'), per the European Society of Endocrinology guidelines. This is distinguished from 'confirmed autonomous cortisol secretion' (>5.0 mcg/dL). The clinical significance lies in the associated increased risk of hypertension, type 2 diabetes, dyslipidemia, osteoporosis, and cardiovascular events. Management involves treating these cardiometabolic comorbidities; adrenalectomy may be considered in younger patients with progressive comorbidities, but is not reflexively indicated. CRH stimulation is used in the differential of ACTH-dependent hypercortisolism, not for adrenal incidentalomas.

A 67-year-old man with type 2 diabetes (HbA1c 8.1%) and an eGFR of 28 mL/min/1.73m² is on metformin 500 mg daily, linagliptin, and insulin glargine 24 units nightly. His nephrologist wants to add an agent for cardiorenal protection. He has a history of hospitalization for heart failure with reduced ejection fraction (HFrEF, EF 35%). Which of the following is most appropriate?

Answer: Add finerenone 10 mg daily

Finerenone (a non-steroidal mineralocorticoid receptor antagonist) is FDA-approved and guideline-recommended for CKD with albuminuria in type 2 diabetes (FIDELIO-DKD and FIGARO-DKD trials), demonstrating reductions in CKD progression and cardiovascular events. Importantly, SGLT2 inhibitors (empagliflozin, dapagliflozin) carry a caution/contraindication when eGFR is <30 mL/min/1.73m² for glycemic benefit, though dapagliflozin is approved down to eGFR ≥25 for heart failure. However, the key distinction: at eGFR 28, finerenone remains appropriate and is preferred when SGLT2i is borderline. Liraglutide (a GLP-1 RA) has cardiovascular outcome data but limited cardiorenal evidence at this eGFR, and its HFrEF data are neutral-to-concerning. Metformin dose adjustment (not discontinuation) is appropriate at eGFR 30–45; at eGFR 28 it should be held, but this question is about adding cardiorenal protection.