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 (pink and white spaces). Osteoclasts (pink) are at centre left. Osteoblasts (cuboidal, pink) are at centre right. The dark red areas are deposits of new bone matrix (osteoid). 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. This condition usually occurs in people over the age of 40. Complications include arthritis and, in rare cases, bone cancer (osteosarcoma). Treatments include injection of a synthetic form of the hormone calcitonin.