A 68-year-old man has an isolated serum alkaline phosphatase of 420 U/L with normal calcium, normal phosphate, and normal PTH. A skull radiograph shows focal areas of lysis and sclerosis with cortical thickening. Bone biopsy reveals a haphazard mosaic pattern of lamellar bone joined by prominent cement lines. What is the diagnosis?

• A Osteopetrosis
• B Fibrous dysplasia
• C Renal osteodystrophy
• D Paget disease of bone ✓

Explanation

Paget disease features disordered, excessive bone remodeling driven first by osteoclastic overactivity, followed by chaotic osteoblast repair. The hallmark histology is a mosaic pattern of lamellar bone with irregular cement lines, and biochemistry classically shows isolated marked elevation of alkaline phosphatase with normal calcium and phosphate. Osteopetrosis shows deficient resorption with retained cartilage cores, and fibrous dysplasia replaces bone with fibrous tissue rather than producing a mosaic lamellar pattern.

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.