In general, there are two types of spots on a bone scan. Hot spots form when radioactive material, or tracer, collects in areas of the bone. Cold spots form in areas where the tracer has not accumulated. Bone loss can cause cold spots, while arthritis, infections, or broken bones can cause hot spots. Tumors and cancer can cause any type.
Some cancers, such as prostate, lung, and breast cancer, cause hot spots on a bone scan when the cancer has metastasized, or spread, to the bone. Bone cancers will also show up as hot spots. These dark areas are due to the growth of excess tissue and the accumulation of the tracer.
Hot spots can also occur due to infections or bone diseases, such as Paget's disease of bone, which causes painful and brittle bones. A person with Paget's does not metabolize bone properly, so old bone can break down faster than new bone. As the disease progresses, new bone forms too quickly to compensate for the deterioration of old bone, and the new tissue does not form completely and may be soft and weak.
Osteomyelitis, a type of bone infection, will also cause hot spots. The infection is usually caused by the bacterium Staphylococcus , which can infect bones and joints. A person can get a bone infection when they get a puncture wound or a broken bone. In some cases, bacteria can enter the body when the broken bone is being treated.
Cold spots on a bone scan indicate that the tracer has not accumulated in that section of bone. A loss of blood flow to the bone, or a bone infarction, can cause this type of stain. When a person has a bone infarction, the part of the bone that no longer receives blood can die and cause it to collapse.
Another cause of cold spots on a scan is multiple myeloma, a type of cancer that causes the body to make too much plasma, or white blood cells. These cells then take over the bone marrow, reducing the number of red blood cells. Plasma cells can also form small tumors in the bone and damage the bone.