A 9-month-old exclusively breastfed infant presents with irritability, reluctance to move the right leg, and subperiosteal hemorrhages on X-ray. Serum alkaline phosphatase is elevated. Serum vitamin C is low. The diagnosis is scurvy. Which clinical sign is pathognomonic of infantile scurvy (Barlow's disease)?
- A Craniotabes (pinging sensation on skull palpation)
- B Frog-leg position of extreme tenderness with pseudo-paralysis ✓
- C Rachitic rosary at the costochondral junctions
- D Bitot's spots at the limbal conjunctiva
Explanation
The pathognomonic sign of infantile scurvy is the frog-leg position: the infant lies with thighs abducted and legs externally rotated with knees semi-flexed due to extreme pain from subperiosteal hemorrhages — movement causes severe pain, producing apparent pseudo-paralysis. This distinguishes scurvy from rickets (rachitic rosary, widened metaphyses) and other conditions. Subperiosteal hemorrhages at the femur, tibia, and humerus are most common radiologically. Craniotabes is a sign of rickets. Bitot's spots occur in vitamin A deficiency. Vitamin C deficiency impairs hydroxylation of proline and lysine in collagen synthesis.
Reference: Ghai Essential Pediatrics, 10th ed.
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