Also Known As: Paget's disease , Paget's disease of bone, Paget's disease, Pagets disease, Paget's, Pagets
Paget's disease of bone is a chronic disorder that can result in enlarged and misshapen bones. The excessive breakdown and formation of bone tissue causes affected bone to weaken, resulting in pain, misshapen bones, fractures, and arthritis in the joints near the affected bones. Paget's disease typically is localized, affecting just one or a few bones, as opposed to osteoporosis, for example, which usually affects all the bones in the body. Decisions about treating Paget's disease can be complicated because 1) no two people are affected in exactly the same way by the disease, and 2) it is sometimes difficult to predict whether a person with Paget's disease who shows no signs of the disorder will develop symptoms or complications (such as a bone fracture) at a later date. Although there is no cure for Paget's disease, medications (bisphosphonates and calcitonin) can help control the disorder and lessen pain and other symptoms. Paget's disease experts recommend that these medications be taken by people with Paget's disease who
- have bone pain, headache, back pain, or a nerve-related symptom (such as "shooting" pains in the leg) that is directly associated with the disease;
- have elevated levels of serum alkaline phosphatase (ALP) in their blood;
- display evidence that a bone fracture will occur;
- require pretreatment therapy for affected bones that require surgery;
- have active symptoms in the skull, long bones, or vertebrae (spine);
- have the disease in bones located next to major joints, placing them at risk of developing osteoarthritis;
- develop hypercalcemia that occurs when a person with several bones affected by Paget's disease and a high serum alkaline phosphtase level is immobilized.
The pathogenesis of Paget's disease is described in 4 stages:
- Osteoclastic activity
- Mixed osteoclastic - osteoblastic activity
- Osteoblastic activity
- Malignant degeneration
Initially, there is a marked increase in the rate of bone resorption at localized areas caused by large and numerous osteoclasts. These localized areas of osteolysis are seen radiologically as an advancing lytic wedge in long bones or osteoporosis circumscripta in the skull. The osteolysis is followed by a compensatory increase in bone formation induced by osteoblasts recruited to the area. This is associated with accelerated deposition of lamellar bone in a disorganized fashion. This intense cellular activity produces a chaotic picture of trabecular bone ("mosaic" pattern), rather than the normal linear lamellar pattern. The resorbed bone is replaced and the marrow spaces are filled by an excess of fibrous connective tissue with a marked increase in blood vessels, causing the bone to become hypervascular. The bone hypercellularity may then diminish, leaving a dense "pagetic bone," also known as burned-out Paget's disease.
Sir James Paget first suggested the disease was due to an inflammatory process. New evidence suggests he may have been correct and that a paramyxovirus infection is the underlying cause of Paget's disease. No infectious virus has yet been isolated as a causative agent, however, and other evidence suggests an intrinsic hyperresponsive reaction to vitamin D and RANK ligand is the cause. Further research is therefore necessary.
Many patients do not know they have Paget's disease because they have a mild case with no symptoms. Sometimes, symptoms may be confused with those of arthritis or other disorders. In other cases, the diagnosis is made only after complications have developed. Symptoms can include:
Paget's disease may be diagnosed using one or more of the following tests:
- Pagetic bone has a characteristic appearance on X-rays. A skeletal survey is therefore indicated.
- An elevated level of alkaline phosphatase in the blood in combination with normal calcium, phosphate, and aminotransferase levels in an elderly patient are suggestive of Paget's disease.
- Markers of bone turnover in urine eg. Pyridinoline
- Elevated levels of serum and urinary hydroxyproline are also found.
- Bone scans are useful in determining the extent and activity of the condition. If a bone scan suggests Paget's disease, the affected bone(s) should be X-rayed to confirm the diagnosis.
Today's medications, especially when started before complications begin, are often successful in controlling the disorder. Paget's disease is rarely diagnosed in people less than 40 years of age. Men are more commonly affected than women (3:2). Prevalence of Paget's disease ranges from 1.5 to 8.0 percent, depending on age and country of residence. Prevalence of familial Paget's disease (where more than one family member has the disease) ranges from 10 to 40 percent in different parts of the world. Because early diagnosis and treatment is important, after age 40, siblings and children of someone with Paget's disease may wish to have an alkaline phosphatase blood test every two or three years. If the alkaline phosphatase level is above normal, other tests such as a bone-specific alkaline phosphatase test, bone scan, or X-ray can be performed.
The outlook is generally good, particularly if treatment is given before major changes in the affected bones have occurred. Any bone or bones can be affected, but Paget's disease occurs most frequently in the spine, skull, pelvis, femur, and lower legs. In general, symptoms progress slowly, and the disease does not spread to normal bones. Treatment can control Paget's disease and lessen symptoms, but is not a cure. Osteogenic sarcoma, a form of bone cancer, is an extremely rare complication that occurs in less than one percent of all patients.
Associated medical conditions
Paget's disease may lead to other medical conditions, including:
- Arthritis may be caused by bowing of long bones in the leg, distorting alignment and increasing pressure on nearby joints. In addition, pagetic bone may enlarge, causing joint surfaces to undergo excessive wear. In these cases, pain may be due to a combination of Paget's disease and osteoarthritis.
- Loss of hearing in one or both ears may occur when Paget's disease affects the skull and the bone that surrounds the inner ear. Treating the Paget's disease may slow or stop hearing loss. Hearing aids may also help.
- Cardiovascular disease can result from severe Paget's disease (i.e. with more than 15% skeletal involvement). Arteriovenous connections can often form in the bone, and so the heart has to work harder (pump more blood) to ensure adequate oxygen supply to the tissues. This increase in cardiac output can lead to calcification of the aortic valve, and the resulting aortic stenosis causes left ventricular hypertrophy and eventually high-output congestive failure.
- Kidney stones are somewhat more common in patients with Paget's disease.
- Pagetic bone can cause nervous system problems, such as pressure on the brain, spinal cord, or nerves, and reduced blood flow to the brain and spinal cord.
- Rarely, Paget's disease is associated with the development of osteosarcoma (malignant tumor of bone). When there is a sudden onset or worsening of pain, sarcoma should be considered.
- When Paget's disease affects the facial bones, the teeth may become loose. Disturbance in chewing may occur.
- Rarely, when the skull is involved, the nerves to the eye may be affected, causing some loss of vision.
- Angioid streaks may develop, possibly as a result of calcification of collagen or other pathological deposition.
Paget's disease is not associated with osteoporosis. Although Paget's disease and osteoporosis can occur in the same patient, they are different disorders. Despite their marked differences, several treatments for Paget's disease are also used to treat osteoporosis.