An 18-month-old boy who was exclusively breastfed without supplementation presents with bowed legs and delayed closure of the anterior fontanelle. X-ray shows cupping and fraying of the metaphyses of the distal radius and femur. Serum studies show low calcium, low phosphate, and elevated alkaline phosphatase. What is the fundamental defect?

• A Excessive osteoclastic resorption of mineralized bone
• B Increased bone density due to failed resorption
• C Reduced osteoblast number with thin osteoid seams
• D Defective mineralization of osteoid matrix ✓

Explanation

Rickets and its adult counterpart osteomalacia result from impaired mineralization of osteoid, classically from vitamin B deficiency causing reduced calcium and phosphate availability. This produces wide unmineralized osteoid seams and metaphyseal cupping and fraying. Osteoporosis has normal mineralization with reduced bone mass, distinguishing it from option C.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.