Paget's Disease

Though many people may not be familiar with it, Paget’s disease of bone (osteitis deformans) as it is formally known, it is the second most common bone disease after osteoporosis. The disease is a disorder of bone metabolism in which the bone remodels itself (breaks down and rebuilds) too quickly. This results in a bony overgrowth at various points as well as problems with the bone’s architecture.

Patients who do have symptoms may complain of pain and have skeletal deformities that occur due to the overgrowth of affected bone.

First described in 1877 by Sir James Paget, Paget’s disease occurs when too much bone is reabsorbed and, as a result, excessive bone is rebuilt in undesirable ways. Sometimes patients have no symptoms, and in these cases, diagnosis may be made by chance, for example when a doctor orders x-rays for another reason. Other times, it can be diagnosed by identifying an enzyme in the blood called bone serum alkaline phosphatase. Patients who do have symptoms may complain of pain and have skeletal deformities that occur due to the overgrowth of affected bone. This feature will explain how Paget’s disease occurs, and how it is diagnosed and treated.

Paget’s disease is estimated to occur in as any as 3.7 percent of people over the age of 40.(1)(2) It seems to increase with age and affects men and women almost equally.(2) Paget’s disease is more common in people of Anglo-Saxon origin (United Kingdom, Australia, New Zealand, North America and Western Europe), and is rare in Asia, India and Scandinavia. About 1% of the population in the United States over the age of 40 years is affected.

Like many other diseases, Paget's is likely the result of a combination of genetic and environmental factors. Up to one-quarter of family members of patients with Paget’s disease eventually contract the disease,(3)(4)(5) with first-degree relatives having seven to ten times greater odds of developing the condition.(5)(6) Several genes have been identified in families with the disease(7)(8)(9)(10)

Viral infection may also play a role in who develops Paget’s disease. Osteoclasts — bone cells that eat up other bone cells for the purpose of "cleaning house" so that new bone can be laid down — from patients with Paget’s disease appear to contain viral particles, which are not found in osteoclasts from healthy individuals.(11)(12)(13)(14) In a small number of patients with Paget’s disease, certain bone and blood cells had virus particles that suggested the measles virus may be at play.(15) Although a relationship between Paget’s disease and the canine distemper virus has been suggested in the owners of unvaccinated dogs, this possibility is controversial.(16)(17).

Osteoclasts — bone cells that eat up other bone cells for the purpose of "cleaning house" so that new bone can be laid down — from patients with Paget’s disease appear to contain viral particles.

When one looks at the bones of Paget’s disease patients under the microscope, they appear "disorganized" because so much bone has been reabsorbed and then replaced at an accelerated rate. There are several other changes that occur,(18)(19) one of which is that the collagen pattern is "immature", compared to the bones of healthy individuals.

Changes in bone remodeling start at one end of the bone and eventually affect the entire bone. The rate of the breakdown of the bone usually occurs at the rate of about 1 cm/year. In the end, a situation known as "burnt out" disease occurs, where the bones are widened and non-uniform in their structure.