A 60-year-old man with newly diagnosed prostate cancer undergoes a bone scan. The radiopharmaceutical used is Tc-99m methylene diphosphonate (MDP). Areas of active bone metastasis will appear as 'hot spots' on the scan. This uptake reflects:

• A Increased regional blood flow only
• B Tumor cell uptake of the tracer directly
• C Increased regional lymphatic drainage
• D Increased osteoblastic activity and bone turnover ✓

Explanation

Tc-99m MDP localizes to areas of increased osteoblastic activity and bone turnover via chemisorption to hydroxyapatite crystals in forming bone matrix. In skeletal metastases, the reactive osteoblastic response surrounding metastatic deposits drives tracer uptake, producing 'hot spots.' This is why predominantly lytic lesions (as in multiple myeloma) may be falsely negative on bone scan, because they suppress rather than stimulate osteoblastic activity. The scan reflects reactive bone formation, not direct tumor uptake.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.