A 20-year-old man from Nigeria has sickle cell anaemia (HbSS). He presents with bilateral hip pain for 3 months, worsening on weight-bearing. X-ray shows subchondral lucency and 'crescent sign' in the femoral head. MRI confirms the diagnosis. What is the most likely diagnosis and the mainstay of medical therapy for sickle cell disease that reduces vaso-occlusive crises?
- A Osteomyelitis of the femoral head — IV antibiotics empirically covering Salmonella
- B Septic arthritis of the hip — immediate joint aspiration and washout
- C Avascular necrosis (AVN) of the femoral head — hydroxyurea is the disease-modifying agent reducing vaso-occlusive crises by increasing HbF ✓
- D Pathological fracture from bone marrow infarction — bisphosphonates for prevention
Explanation
Avascular necrosis (AVN) of the femoral head is a common skeletal complication of sickle cell disease, caused by vascular occlusion and ischaemia of the femoral head. The crescent sign on X-ray represents subchondral bone collapse — a late feature. Hydroxyurea (hydroxycarbamide) is the cornerstone disease-modifying therapy for SCD, increasing HbF production (via induction of HbF-promoting pathways in erythroid precursors), which inhibits HbS polymerisation, reducing vaso-occlusive crises, acute chest syndrome, and hospitalisation rates. Salmonella is the classic organism in sickle cell osteomyelitis but AVN has distinct imaging features (crescent sign, subchondral lucency without periosteal reaction).
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.