PLAB 1 Diagnosis & Investigation Interpretation 2

Question 1

A 45-year-old woman has a urinalysis showing: blood 3+, protein 2+, red cell casts on microscopy. What does the presence of red cell casts indicate?

Accepted Answer

Glomerulonephritis

Answer

Red cell casts form in the renal tubules when red cells leak through a damaged glomerular basement membrane into the tubular lumen. Their presence is pathognomonic of glomerulonephritis (glomerular inflammation). Haematuria with red cell casts always requires urgent nephrology investigation.

Question 2

A plain abdominal X-ray shows dilated loops of large bowel (>6cm) with loss of haustral markings and a 'coffee bean' sign. What is the most likely diagnosis?

Accepted Answer

Sigmoid volvulus

Answer

The coffee bean (or kidney bean) sign on AXR, with a very dilated loop of large bowel devoid of haustra, pointing to the right upper quadrant, is characteristic of sigmoid volvulus — twisting of the sigmoid colon on its mesentery. It requires urgent sigmoidoscopic decompression or surgery.

Question 3

A 60-year-old man has serum calcium 2.9 mmol/L, PTH 8.5 pmol/L (elevated), and phosphate 0.6 mmol/L. What is the most likely diagnosis?

Accepted Answer

Primary hyperparathyroidism

Answer

Primary hyperparathyroidism: hypercalcaemia with inappropriately elevated PTH (which should be suppressed in the context of high calcium) and hypophosphataemia (PTH causes phosphate excretion). Malignancy causes hypercalcaemia with suppressed PTH. This is the classic biochemical picture of primary hyperparathyroidism.

Question 4

An MRI of the lumbar spine shows a central disc prolapse at L4/5 compressing the cauda equina. The patient reports saddle anaesthesia and urinary retention. What is the immediate management?

Accepted Answer

Emergency surgical decompression — this is cauda equina syndrome

Answer

Cauda equina syndrome (CES) is a surgical emergency. Features: saddle anaesthesia (perineum, genitalia, inner thighs), bladder/bowel dysfunction, bilateral leg weakness/numbness. Delays to surgical decompression cause permanent neurological damage. Once suspected clinically, emergency MRI confirms and emergency surgery is required.

Question 5

A blood film shows hypersegmented neutrophils (>5 lobes) and macro-ovalocytes. Hb 75 g/L, MCV 115 fL. What is the most likely diagnosis?

Accepted Answer

Megaloblastic anaemia (B12 or folate deficiency)

Answer

Megaloblastic anaemia is characterised by: macrocytosis (high MCV), macro-ovalocytes, and hypersegmented neutrophils (≥5 lobes in >5% of neutrophils, or any with ≥6 lobes). It is caused by B12 or folate deficiency, both essential for DNA synthesis. The blood film picture is pathognomonic.

PLAB 1 Practice Test

PLAB 1 Practice Test

PLAB 1 Diagnosis & Investigation Interpretation 2