Bone is an active tissue. It is constantly undergoing replacement, as new bone is formed, and old bone is absorbed.
This process is known as bone remodeling. Paget's disease is a bone remodeling disorder.
Bone remodeling normally occurs without problems, but if the process goes wrong, abnormal bone can result.
In Paget's disease, new bone is placed where it is not needed, and old bone is removed where it is needed. This is called dysregulation, and it can distort the normal skeletal structure.
The excessive breakdown and formation of bone tissue that happen with Paget's disease can cause weak bones, bone pain, arthritis, deformities, and fractures. Many people with Paget's disease do not realize that they have it, because symptoms are either mild or not detectable.
If a person with Paget's disease fractures a bone, it may take a long time to heal, because of the abnormalities in bone renewal.
How common is Paget's disease?
In Paget's disease, the breakdown and reforming of bone no longer works properly.
Paget's disease is more common among certain populations. People living in the United Kingdom, Western Europe, and the United States are more likely to have it, but it is very uncommon in Scandinavia, China, and India.
Paget's disease is most commonly diagnosed in people over the age of 40 years. The risk increases with age. It affects men slightly more than women. For every two women that have it, there are three men.
In the UK, it affects 8 percent of men and 5 percent of women by the age of 80 years.
Cases of Paget's disease are generally mild, and most patients receive a diagnosis as a result of an x-ray for an unrelated reason.
What are the causes of Paget's disease?
The cause of Paget's disease is not entirely known.
There appears to be a family connection. According to the American College of Rheumatology, in 30 percent of cases, more than one family member has the condition.
Another hypothesis is that it stems, in part, from the measles virus, contracted during childhood.
A virus particle, known as a paramyxovirus nucleocapsid, has been identified inside the bone cells of some patients with Paget's disease. Measles is a paramyxovirus. This virus particle is not found in normal bone. However, a clear connection between the virus and Paget's disease has not yet been confirmed.
However, it is known that the virus may lay dormant for years before reactivating and attacking the osteoclast cells, causing them to malfunction.
There is evidence that the number of people with Paget's disease is falling. If the disorder were only caused by genetic mutations, the number of new cases stay relatively stable or would increase. This suggests that environmental factors may play a role.
The drop in the number of cases of Paget's disease could relate to a fall in the number of measles infections, because of the measles vaccination programs.
Symptoms of Paget's disease?
Many patients do not know they have Paget's disease, because they have no symptoms, or because symptoms are confused with those of arthritis or other disorders.
Paget's disease of bone mostly affects the long bones, and it can cause bone pain.
When people experience symptoms, the most common ones relate to bone or joint pain. They may also have swelling of joints, tenderness, or redness, over the affected areas.
Some people only know they have Paget's disease when they experience a fracture in a weakened bone.
The most common bones affected by Paget's disease are the pelvis, spine, skull, femur, or thigh bone, and tibia, or shin bone.
Many major nerves in the body run through or alongside the bones, so abnormal bone growth can cause a bone to compress, "pinch" or damage a nerve.
Other complications include arthritis and hearing problems.
Diagnosing Paget's disease
Paget's disease is diagnosed through physical examination, x-rays, and laboratory studies.
The physical examination may show abnormalities of the skeletal shape or bone deformities.
X-rays can reveal abnormalities of bone turnover, including areas of increased and decreased bone deposition.
Laboratory studies show an increased level of alkaline phosphatase, a byproduct of bone formation. Calcium levels within the body are usually normal.
Treatment can control Paget's disease and lessen symptoms, but there is no cure.
Not all patients with Paget's disease will need treatment, but if there are symptoms, or if laboratory tests show that treatment is necessary, the first line of treatment will normally be bisphosphonates. Vitamin D and calcium are given to supplement.
Bisphosphonates will help to reduce the breakdown of disordered bone. Patients who are receiving bisphosphonates also need to maintain adequate levels of vitamin D and calcium.
The Institute of Medicine of the National Academy of Sciences recommends that, to keep bones healthy, all women aged 50 and older and men aged 70 years and older should consume 1,200 mg of calcium and at least 600 IU (International Units) of vitamin D a day. From 70 years, they recommend increasing vitamin D intake to 800 IU a day.
Exposure to sunlight is also recommended, to enable the synthesis of vitamin D.
Oral bisphosphonates and calcium should be taken at least 2 hours apart, because the calcium can reduce the absorption of bisphosphonate.
Bisphosphonates and calcium can protect the weak parts of bone that cause deformity and are at high risk for being fractured.
If a patient has previously had kidney stones, they should talk to their physician before increasing their intake of calcium and vitamin D.
Surgery for Paget's disease
Surgery may be necessary if there is a significant bone deformity or a break in the bone.
Fractures are most common in the femur, or thigh bone and the tibia, or shin bone.
They are usually treated with an intramedullary rod. This is a rod that is inserted into the marrow cavity in the center of the bone.
Another common surgery in patients with Paget's disease is an osteotomy. In this procedure, a wedge of bone is removed to correct a malalignment. It is often necessary when the bones of the legs become misshapen in the later stages of this disease.
The outlook with Paget's disease is generally good, particularly if patients receive treatment before major changes occur in the affected bones.
Preventing Paget's disease
Paget's Disease is unavoidable in most cases, but exercise can help to maintain skeletal health, avoid weight gain, and maintain joint mobility.
People with the disease should talk to their physician before starting any exercise program, because they should not put more stress than necessary on affected bones.