MRCP Part 1 Endocrinology & Renal Medicine

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?

Accepted Answer

Hyperosmolar hyperglycaemic state

Answer

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?

Accepted Answer

21-hydroxylase deficiency

Answer

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?

Accepted Answer

Nephrogenic diabetes insipidus

Answer

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?

Accepted Answer

Overnight 1mg dexamethasone suppression test

Answer

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?

Accepted Answer

Hypoparathyroidism

Answer

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.

MRCP Part 1 Practice Test

MRCP Part 1 Practice Test

MRCP Part 1 Endocrinology & Renal Medicine