A 70-year-old woman with Paget's disease of bone presents with bowing of the left femur, hearing loss, and serum alkaline phosphatase of 950 U/L. The most sensitive biochemical marker for monitoring treatment response to bisphosphonate therapy in Paget's disease is:

• A Serum calcium
• B Urinary hydroxyproline
• C Serum osteocalcin
• D Serum total alkaline phosphatase (ALP) — normalisation indicates remission ✓

Explanation

Serum total alkaline phosphatase (ALP) is the standard marker for disease activity and treatment response in Paget's disease; it reflects osteoblastic overactivity that parallels the accelerated bone remodelling. Treatment (zoledronic acid 5 mg IV — now the preferred bisphosphonate for its single-infusion convenience and prolonged remission) aims to normalise ALP levels. P1NP (procollagen type I N-terminal propeptide) is a more specific bone formation marker but ALP is widely available and cost-effective. Urinary hydroxyproline (collagen degradation) was older practice.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.