The cause of Paget's disease is unknown. There are theories about early viral infection and genetic causes. The disease occurs worldwide, but is more common in Europe, Australia, and New Zealand -- where it is seen in up to 5% of the elderly population. The disease is characterized by excessive breakdown of bone tissue, followed by abnormal bone formation. The new bone is structurally enlarged, but weakened and filled with new blood vessels. The disease may localize to one or two areas within the skeleton, or become widespread. Frequently, bones of the pelvis, leg, spine, arm, or the collar bone are involved. The effect on the skull may enlarge head size and cause hearing loss, if the cranial nerves are damaged by the bone growth.
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