A bone scan (bone scintigraphy) using Technetium-99m MDP (Tc-99m methylene diphosphonate) is one of the most widely performed nuclear medicine studies. It evaluates bone turnover and perfusion and is highly sensitive for detecting skeletal pathology, often before structural changes are visible on X-ray or CT.
📌 How It Works
- Tracer: Tc-99m MDP binds to hydroxyapatite crystals in areas of increased osteoblastic activity.
- Phases:
- Flow phase (perfusion).
- Blood pool phase (soft tissue hyperemia).
- Delayed phase (osseous uptake).
✅ Indications of Bone Scan
1. Oncology
- Detection of bone metastases (most common indication).
- Staging and follow-up in breast, prostate, lung, thyroid, renal, etc.
- Differentiating benign vs malignant lesions (helps but not always specific).
2. Infection & Inflammation
- Evaluation of osteomyelitis.
- Prosthetic joint infection vs loosening (often combined with labeled WBC scan).
- Septic arthritis.
3. Trauma
- Detection of occult or stress fractures (when X-ray is negative).
- Fractures in polytrauma patients.
- Evaluation of suspected child abuse (skeletal survey).
4. Metabolic Bone Disease
- Paget’s disease.
- Fibrous dysplasia.
- Metabolic bone disorders (renal osteodystrophy, hyperparathyroidism).
5. Joint & Vascular Conditions
- Reflex sympathetic dystrophy (CRPS).
- Avascular necrosis (early detection, though MRI is preferred now).
- Arthritis (inflammatory and degenerative).
6. Post-treatment Evaluation
- Response assessment after therapy (e.g., chemotherapy, bisphosphonates).
- Detection of recurrence or progression in skeletal disease.
⚡ Teaching Pearls
- Bone scan = high sensitivity, low specificity → positive uptake means increased bone turnover but etiology (tumor, infection, fracture) needs correlation with MRI/CT.
- SPECT or SPECT-CT improves localization and specificity.
- Negative bone scan = almost rules out metastatic disease (except purely lytic lesions like myeloma).
🗂️ Flowchart: Indications for Nuclear Bone Scan
When to Order a Bone Scan?
➡️ Oncology
- Detect bone metastases (breast, prostate, lung, thyroid, renal)
- Staging & follow-up of cancers
- Monitor treatment response
➡️ Infection & Inflammation
- Osteomyelitis
- Prosthetic joint infection vs loosening
- Septic arthritis
➡️ Trauma
- Occult/stress fractures (X-ray negative)
- Fractures in polytrauma
- Suspected child abuse
➡️ Metabolic Bone Disease
- Paget’s disease
- Fibrous dysplasia
- Renal osteodystrophy / hyperparathyroidism
➡️ Joint & Vascular Disorders
- Arthritis (RA, OA)
- Reflex sympathetic dystrophy (CRPS-Complex Regional Pain Syndrome)
- Early avascular necrosis (MRI more sensitive, but bone scan can detect early perfusion change)
➡️ Post-treatment / Follow-up
- Assess recurrence
- Therapy monitoring (e.g., chemotherapy, bisphosphonates)
✅ Key Takeaway:
Bone scan is highly sensitive for detecting bone pathology, but not specific → always correlate with X-ray, CT, or MRI.