Bone scan of a patient with Multiple Myeloma shows

A bone scan is a nuclear scanning test that detects areas of increased or decreased bone metabolism. Radionuclide isotope used is technetium-99. It is linked to a bone-seeking phosphate compound. Thus Technetium-labelled hydroxy methylene diphosphonate ( 99mTc-HDP) is injected intravenously and its activity recorded by a gamma camera at two stages - 1. shortly after injection, while it is still in the bloodstream or the perivascular space (the perfusion or blood pool phase) 2. 3 hours later when the isotope has been taken up in bone (the bone phase) 4 types of abnormality are seen - a. Increased activity in the perfusion phase this is due to increased soft tissue blood ow - one of the cardinal features of inflammation (eg. acute or chronic synovitis) b. Decreased activity in the perfusion phase This is much less common and signifies local vascular insufficiency c. Increased activity in the bone phase This is due to either excessive isotope uptake in the osseous extracellular uid or to more avid incorporation into newly forming bone tissue. There are several possible reasons for bone activity - cancer is one of them, but other reasons include arthritis, fractures and bone infections and nothing in the bone scan itself can distinguish between them. d. Diminished activity in the bone phase This is due to absent blood supply eg. in the femoral head after a fracture of the femoral neck or to a replacement of bone by pathological tissue. Increased uptake on bone scans 1. Metastatic disease - multiple, randomly scattered lesions, especially in the axial skeleton. 2. Joint disease - commonly degenerative in the cervical spine, hips, hands and knees. Also, inflammatory joint disease. 3. Fractures - stress fractures or other undisplaced fractures undetected on plain x-ray. 4. Paget's disease - diffuse involvement with much-increased uptake. 5. Superscan - high uptake throughout the skeleton often due to disseminated secondary disease with poor or absent renal images but often with bladder activity. 6. Metabolic bone disease - high uptake in the axial skeleton, proximal long bones, with prominent calvarium and mandible. 7. Dental disease - inflammation, recent extraction. 8. Infection - increased uptake in vascular and blood pool phase also. Photopenic areas (defects) on bone scans 1. Artifacts - the commonest cause. a. External - metal objects such as coins, belts, lockets, buckles. b. An internal - joint prosthesis, pacemakers. 2. Avascular lesions - for example cysts. 3. Multiple myelomas - may show increased uptake. 4. Leukemia - may show increased uptake. 5. Haemangiomas of the spine - occasionally slightly increased uptake. 6. Radiotherapy elds - usually oblong in shape. 7. Advanced cancer - especially breast. Possibly related to chemotherapy. 8. Spina bifida