MRCP Part 1 Endocrinology & Renal Medicine 1 — Questions and Answers
Question 1: A patient with known type 2 diabetes presents with confusion, blood glucose 58 mmol/L, and serum osmolality 360 mOsm/kg. There is no ketoacidosis. What is the diagnosis?
- Diabetic ketoacidosis
- Hyperosmolar hyperglycaemic state (Correct answer)
- Lactic acidosis
- Euglycaemic DKA
Correct answer: Hyperosmolar hyperglycaemic state
Hyperosmolar hyperglycaemic state (HHS) is characterised by severe hyperglycaemia (>30 mmol/L), hyperosmolality (>320 mOsm/kg), dehydration, and absence of significant ketoacidosis. It typically occurs in elderly type 2 diabetic patients and carries higher mortality than DKA.
Question 2: Which enzyme deficiency most commonly causes congenital adrenal hyperplasia?
- 11-beta-hydroxylase deficiency
- 21-hydroxylase deficiency (Correct answer)
- 17-alpha-hydroxylase deficiency
- 3-beta-hydroxysteroid dehydrogenase deficiency
Correct answer: 21-hydroxylase deficiency
21-hydroxylase deficiency accounts for approximately 90–95% of congenital adrenal hyperplasia (CAH). It impairs the conversion of 17-hydroxyprogesterone to cortisol and aldosterone, causing cortisol deficiency, aldosterone deficiency, and excess androgen production.
Question 3: A patient on long-term lithium therapy presents with polyuria and polydipsia. Plasma osmolality is high but urine osmolality is low and does not concentrate after DDAVP administration. What is the diagnosis?
- Central diabetes insipidus
- Nephrogenic diabetes insipidus (Correct answer)
- Primary polydipsia
- SIADH
Correct answer: Nephrogenic diabetes insipidus
Lithium is the most common drug cause of nephrogenic diabetes insipidus. It impairs renal tubular response to ADH by blocking aquaporin-2 insertion. Failure to concentrate urine after DDAVP confirms nephrogenic (rather than central) DI, where DDAVP would restore urine concentration.
Question 4: Which investigation is the gold standard for diagnosing Cushing's syndrome?
- Single morning cortisol
- 24-hour urinary free cortisol
- Overnight 1mg dexamethasone suppression test (Correct answer)
- ACTH stimulation test
Correct answer: Overnight 1mg dexamethasone suppression test
The overnight low-dose dexamethasone suppression test (1mg at midnight, cortisol at 9am) is the most commonly used first-line screening test. In healthy individuals, cortisol is suppressed to <50 nmol/L. Failure to suppress suggests autonomous cortisol secretion. Multiple tests may be needed.
Question 5: A patient is found to have a serum calcium of 2.95 mmol/L, low PTH, and high phosphate. What is the most likely diagnosis?
- Primary hyperparathyroidism
- Hypoparathyroidism (Correct answer)
- Sarcoidosis
- Hypercalcaemia of malignancy
Correct answer: Hypoparathyroidism
Low PTH with high phosphate and hypercalcaemia (or hypocalcaemia) in the context of low PTH indicates hypoparathyroidism. Wait — in hypoparathyroidism, calcium is LOW. If calcium is high with low PTH and high phosphate, consider vitamin D toxicity or granulomatous disease. A low PTH with hypocalcaemia and hyperphosphataemia is hypoparathyroidism.
Question 6: Which drug used for type 2 diabetes has been shown to reduce cardiovascular death and hospitalisation for heart failure in patients with established CVD?
- Glipizide
- Sitagliptin
- Empagliflozin (Correct answer)
- Pioglitazone
Correct answer: Empagliflozin
SGLT2 inhibitors, particularly empagliflozin (EMPA-REG OUTCOME trial) and canagliflozin (CANVAS trial), have demonstrated significant reductions in cardiovascular death, hospitalisation for heart failure, and renal progression in patients with type 2 diabetes and established CVD or high CV risk.
MRCP Part 1 Endocrinology & Renal Medicine 1
A patient with known type 2 diabetes presents with confusion, blood glucose 58 mmol/L, and serum osmolality 360 mOsm/kg.
There is no ketoacidosis.
What is the diagnosis?