OncologyTier 2Topic

Nuclear bone scan

Principle

Bone scintigraphy (technetium-99m-labelled bisphosphonate) detects areas of increased bone turnover - the traditional whole-body screening test for bone metastases, though increasingly supplemented or replaced by PET/MRI in some settings
Most useful for cancers with a high propensity for osteoblastic (sclerotic) bone metastasis - prostate cancer is the classic and most frequent indication
The tracer accumulates at sites of active bone remodelling/osteoblastic activity, not the tumour cells themselves - so the scan is a marker of the bone's reactive response to a lesion, not a direct image of tumour tissue

"Hot spots" (increased tracer uptake) are sensitive for bone metastases but non-specific - degenerative joint disease, fracture, and infection all produce increased uptake and can mimic metastatic disease, particularly in the spine
Purely osteolytic (lytic) metastases (e.g. some myeloma, renal cell carcinoma) can be falsely negative on bone scan, since the technique depends on an osteoblastic reactive response that lytic-predominant disease may not generate - CT or MRI is preferred when lytic disease is suspected

Correlate any hot spot with plain film/CT/MRI of the corresponding site to distinguish metastatic disease from a benign cause (degenerative change, old fracture, Paget's disease)
Used for staging at diagnosis in cancers with high bone metastasis risk (prostate, breast) and for monitoring response to treatment (though a "flare" phenomenon - a transient increase in uptake reflecting a healing response rather than progression - can complicate early post-treatment interpretation)

Prostate cancer, breast cancer, multiple myeloma (often falsely negative given lytic pattern - skeletal survey or whole-body MRI preferred), Paget's disease (a benign mimic)

The bone scan flare phenomenon after starting effective treatment (increased uptake in the first weeks, reflecting bone healing rather than disease progression) is a recognised interpretive trap - repeat imaging after a longer interval clarifies true response versus progression

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