What are the indications for a bone scan?

Bone Scan Indications

Bone scintigraphy is indicated for detecting skeletal metastases in cancer patients at high risk for bone involvement, specifically those with symptomatic disease or high-risk tumor characteristics, but should generally be avoided in asymptomatic patients with PSA <10 ng/mL or early-stage disease.

Primary Indications for Bone Scan

Cancer Staging and Detection of Bone Metastases

High-Risk Prostate Cancer:

• T1 disease with PSA ≥20 ng/mL 1
• T2 disease with PSA ≥10 ng/mL 1
• Gleason score ≥8 at any stage 1
• T3/T4 disease (locally advanced or advanced disease) 1
• Any stage with symptoms suggestive of osseous metastatic disease 1

Breast Cancer:

• All patients with signs or symptoms of bone metastases 1
• Advanced breast cancer for staging 1
• Patients with persistent or localized bone pain 1
• Large tumors with aggressive biology 1

Lung Cancer (NSCLC):

• Locally advanced disease 1
• Patients with signs or symptoms of bone metastases 1
• Advanced NSCLC staging (though PET/CT may be preferred) 1

Renal Cell Carcinoma:

• Only in patients with suspected bone metastases based on symptoms or biochemical markers 1

Post-Treatment Surveillance

After Radical Prostatectomy:

• Failure of PSA to fall to undetectable levels post-operatively 1
• Undetectable PSA that becomes detectable and increases on 2 subsequent determinations 1

After Radiation Therapy:

• Rising PSA or positive digital rectal examination if patient is candidate for additional local therapy 1

When Bone Scan is NOT Indicated

Avoid bone scanning in:

• Asymptomatic men with PSA <10 ng/mL (rarely positive) 1
• Low-risk prostate cancer without symptoms 1
• Early-stage breast cancer (Stage I-II) without symptoms 2
• Renal cell carcinoma without clinical suspicion 1

Clinical Context and Limitations

Sensitivity and Specificity Considerations:

• Bone scintigraphy is more sensitive than plain radiography for detecting skeletal pathology but has low specificity 1
• Equivocal findings or small number of hot spots require confirmation with other imaging modalities (MRI, CT, or PET/CT) 1
• MRI is more sensitive than bone scintigraphy and is preferred for early detection of spinal cord metastases 1

Alternative Imaging:

• PET/CT may be used as an alternative to bone scintigraphy in some guidelines for breast cancer and NSCLC 1
• PET/CT shows comparable or superior diagnostic accuracy to bone scan, particularly for osteolytic metastases 3, 4
• For inconclusive bone scan results, consider MRI or PET/CT for further evaluation 1, 5

Important Caveats

Risk-Benefit Assessment:

• Frequency of imaging should be based on individual risk factors including age, PSA doubling time, Gleason score, and overall health 1
• Low- and intermediate-risk groups with low serum PSAs post-operatively have very low risk of positive bone scans 1

Biochemical Markers:

• Elevated bone-specific alkaline phosphatase (B-ALP) is an indicator for bone metastases and may warrant bone imaging 1
• In prostate cancer, elevated PSA combined with elevated B-ALP suggests bone involvement 1

Symptomatic Patients:

• Any patient with localized bone pain, suspected pathologic fracture, or neurologic symptoms should undergo bone imaging regardless of other risk factors 1, 5
• Plain radiography is useful for evaluating symptomatic regions and assessing fracture risk 1