PLAB 1 Musculoskeletal Medicine & Rheumatology 3

Question 1

A 62-year-old man presents with acute knee pain and swelling. Joint aspiration reveals positively birefringent rhomboid-shaped crystals under polarised light microscopy. What is the diagnosis?

Accepted Answer

Pseudogout (calcium pyrophosphate deposition)

Answer

Pseudogout is caused by calcium pyrophosphate dihydrate (CPPD) crystals, which appear positively birefringent and rhomboid-shaped under polarised light, unlike the negatively birefringent needle-shaped urate crystals of gout.

Question 2

A patient with a known diagnosis of rheumatoid arthritis is to be started on an anti-TNF biologic agent. Which pre-treatment screening is MOST important before initiating therapy?

Accepted Answer

Tuberculosis screening (IGRA or Mantoux)

Answer

TB screening with an interferon-gamma release assay (IGRA) or Mantoux test is mandatory before starting anti-TNF therapy, as these agents can reactivate latent tuberculosis causing life-threatening disease.

Question 3

What is the mechanism of action of allopurinol in the management of gout?

Accepted Answer

Inhibits xanthine oxidase, reducing uric acid production

Answer

Allopurinol inhibits xanthine oxidase, the enzyme that converts hypoxanthine and xanthine to uric acid, thereby reducing urate production and serum uric acid levels.

Question 4

A 38-year-old woman with SLE and confirmed antiphospholipid syndrome has had two consecutive first-trimester miscarriages. What is the recommended management during her next pregnancy?

Accepted Answer

Low-dose aspirin plus low molecular weight heparin (LMWH)

Answer

Women with antiphospholipid syndrome and recurrent pregnancy loss require low-dose aspirin and LMWH throughout pregnancy; warfarin is teratogenic in the first trimester and avoided.

Question 5

A 65-year-old woman with a history of RA and chronic kidney disease develops a severe skin rash after starting allopurinol. What interaction must be warned about when prescribing allopurinol alongside azathioprine?

Accepted Answer

Allopurinol inhibits azathioprine metabolism, causing potentially fatal toxicity

Answer

Allopurinol inhibits xanthine oxidase, which also metabolises azathioprine; co-administration causes azathioprine accumulation leading to severe bone marrow suppression and potentially fatal toxicity.

PLAB 1 Practice Test

PLAB 1 Practice Test

PLAB 1 Musculoskeletal Medicine & Rheumatology 3