How can you distinguish between cellulitis and osteomyelitis on a scan?

The rationale behind distinguishing between cellulitis and osteomyelitis using a 5-hour scan focuses on the differences in how these two conditions present in imaging studies. Osteomyelitis, which is an infection of the bone, typically results in increased uptake on bone scans due to the presence of increased metabolic activity associated with the infection and surrounding inflammatory response. This can be detected as "hot" areas on the scan.

In contrast, cellulitis primarily affects the soft tissues and does not alter bone metabolism directly. Therefore, on a 5-hour scan, cellulitis may show normal results because it doesn't involve changes in bone that would lead to increased radiopharmaceutical uptake.

This understanding is crucial in clinical practice as it helps healthcare professionals accurately diagnose the underlying condition and determine the appropriate treatment. Thus, a 5-hour scan will indeed appear "hot" if osteomyelitis is present and may return normal if only cellulitis is involved, confirming why this choice is the correct answer.