Not to be confused with Paget's Disease of the Breast, Paget's disease, discovered by Sir James Paget, is a bone disease that affects elderly men and women. It is characterized by the softening and inappropriate growth of bones. The most commonly affected areas are the skull, the collar bones, the pelvis, the spine, and occasionally the leg bones, which may cause bow-legged-ness. When it involves the skull or upper spine it can cause severe headaches and sometimes paralysis as the new deformed bone growth compresses vital nerves in that area. Resulting pain is treated with standard pain-relievers, and the bone growth can be slowed with calcitonin, a hormone that causes phosphorus and calcium - vital bone building material - to be safely dumped out in urine. Paget's disease is believed to be caused by a viral infection.