In PET-CT using F-18 fluorodeoxyglucose (FDG), a 'flare phenomenon' may be seen after initiating treatment for bone metastases. What does this represent?

• A New bone metastases developing despite treatment
• B Increased FDG uptake in healing/reparative bone activity as a response to successful treatment ✓
• C Radiation-induced osteonecrosis at the treatment site
• D Disease progression with new cortical destruction

Explanation

The 'flare phenomenon' on bone scintigraphy (and to a lesser extent PET-CT) describes temporarily increased tracer uptake in known bone metastases shortly after initiating effective therapy. It reflects increased osteoblastic repair activity and inflammation as bone responds to successful treatment — a paradoxical increase that can be mistaken for disease progression. It is typically seen 1–3 months after starting therapy and resolves on later scans. True progression shows new lesions or persistently increasing uptake beyond the flare period.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.