PLAB 1 Diagnosis & Investigation Interpretation 2 — Questions and Answers
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?
- Bladder carcinoma
- Glomerulonephritis (Correct answer)
- UTI
- Renal calculi
Correct answer: Glomerulonephritis
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?
- Paralytic ileus
- Sigmoid volvulus (Correct answer)
- Caecal volvulus
- Large bowel obstruction at splenic flexure
Correct answer: Sigmoid volvulus
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?
- Malignancy-related hypercalcaemia
- Primary hyperparathyroidism (Correct answer)
- Secondary hyperparathyroidism
- Sarcoidosis
Correct answer: Primary hyperparathyroidism
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?
- Oral analgesia and physiotherapy referral
- Emergency surgical decompression — this is cauda equina syndrome (Correct answer)
- IV methylprednisolone
- Conservative management and MRI surveillance
Correct answer: Emergency surgical decompression — this is cauda equina syndrome
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?
- Iron deficiency anaemia
- Megaloblastic anaemia (B12 or folate deficiency) (Correct answer)
- Haemolytic anaemia
- Aplastic anaemia
Correct answer: Megaloblastic anaemia (B12 or folate deficiency)
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.
Question 6: A 50-year-old man has an elevated ALP with normal ALT, AST, and GGT. Bone scan shows increased uptake in multiple areas of the pelvis and skull. What is the most likely diagnosis?
- Liver metastases
- Paget's disease of bone (Correct answer)
- Myeloma
- Primary hyperparathyroidism
Correct answer: Paget's disease of bone
Paget's disease of bone causes isolated elevation of ALP (from increased osteoblast activity) with normal liver function (GGT is normal, distinguishing it from liver disease). Bone scan shows characteristic intense uptake in affected bones. The skull and pelvis are commonly affected.
PLAB 1 Diagnosis & Investigation Interpretation 2
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?