A 65-year-old male is found to have Paget's disease of bone (polyostotic) on X-ray. Which biochemical parameter is the MOST sensitive marker for monitoring disease activity and treatment response?

• A Serum calcium
• B Serum alkaline phosphatase (total or bone-specific) ✓
• C Serum phosphorus
• D Urinary hydroxyproline

Explanation

In Paget's disease, osteoblastic activity is massively upregulated in response to primary osteoclastic hyperactivity; serum total alkaline phosphatase (ALP) — or more specifically bone-specific ALP — is elevated proportionately to disease extent and reflects the coupled osteoblastic response. It is the standard biochemical marker for diagnosis, disease extent, and monitoring treatment response to bisphosphonates (zoledronic acid first line). Serum calcium and phosphorus are typically normal in uncomplicated Paget's. Urinary hydroxyproline reflects collagen degradation but is less sensitive and less commonly used than ALP.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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