Paget's disease. Light micrograph of a section through bone tissue in Paget's disease. Areas of mineralised bone (blue) have formed around bone-forming cells and lacunae (red and white spaces). Also called osteitis deformans, this is a painful disorder which causes excessive breakdown and formation of bone, causing bones to weaken, thicken, and become deformed. Here, the bone formation is greater than normal and has produced irregular mineralisation. This condition usually occurs in people over the age of 40. Complications include arthritis and, in rare cases, bone cancer (osteosarcoma). Usually the pelvis, collarbone, backbone, and leg bones are affected. Treatments include injection of a synthetic form of the hormone calcitonin.