Conditions such as arthritis, bone cancer, bone infection and bone trauma can cause dark spots to show during a bone scan, according to the Johns Hopkins Medicine Health Library. These spots typically occur in areas where cells rapidly multiply.
Drugs.com defines bone scans as tests that look for abnormal bone cell metabolism. The test involves the injection of a tracer. According to WebMD, it may take between two to five hours for the tracer to bind to the bones. After the wait period, the patient is asked to drink up to six glasses of water to flush out excess tracer. The patient then lies down on a table where a large camera slowly scans the bones.
WebMD explains that a normal scan shows the tracer evenly distributed throughout the bones. Dark spots, also known as hot spots, show where the tracer collects in the bone. This occurs in areas that are healing or have abnormal growth patterns.
Bone scans are just one of many tools a physician uses to diagnose an illness. Though bone scans may show abnormalities, explains Mayo Clinic, they do not show what causes the problems. According to WebMD, a physician also considers the symptoms and results of other tests, such as X-rays, before making a diagnosis.