What is Paget’s disease of bone? What causes Paget’s disease?

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MNT Knowledge Center

After osteoporosis (brittle bones), Paget’s disease is the second most common type of bone disease. The disease is named after Sir James Paget, the British surgeon who first described it in 1877.

Paget’s disease is known as a bone remodeling disorder. Bone may seem like a very inactive tissue, but bone is constantly undergoing ‘turnover’ or replacement. New bone is formed, and old bone is absorbed. This process is known as bone remodeling.

In most people this remodeling process occurs without problems. However, the process can go awry and create abnormalities of the bone. In Paget’s disease, the bone remodeling process is disregulated. New bone is placed where it is not needed, and old bone is removed where it is needed. This disregulation can distort the normal skeletal architecture. The excessive breakdown and formation of bone tissue that occurs with Paget’s disease can cause bone to weaken, resulting in bone pain, arthritis, deformities, and fractures.

Paget’s disease is more common in certain geographical locations, specifically England, Western Europe, and the United States. It is very uncommon in Scandinavia, China, and India. Paget’s disease is most commonly diagnosed in the sixth decade, and increases in prevalence as age increases. Paget’s disease is very uncommon in individuals under 40 years of age. It is estimated that 1-2% of white adults who are over 55 years of age have Paget’s disease. This figure rises to 5-8% for white people who are over 80 years of age.

In most cases, Paget’s disease is a mild disease that does not cause any problems or complications. In fact, about 80% of individuals are diagnosed with Paget’s disease following an x-ray performed for an unrelated reason.

What are the symptoms Paget’s Disease?

A symptom is something the patient senses and describes, while a sign is something other people, such as the doctor notice. For example, drowsiness may be a symptom while dilated pupils may be a sign.

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.

In individuals who do experience symptoms from Paget’s disease, the most common complaints relate to bone or joint pain. Other common symptoms include swelling of joints, tenderness or redness over the affected areas, and occasionally individuals will not know of Paget’s disease until experiencing a fracture through a weakened area of bone.

The most common bones affected by Paget’s disease are the pelvis, femur (thigh bone), spine, skull, and tibia (shin bone).

Many of the major nerves in your body run through or alongside your bones. Therefore, abnormal bone growth can result in a bone compressing, ‘pinching’ or damaging a nerve.

What are the causes of Paget’s Disease?

The cause of Paget’s disease is not entirely known, but it is thought to be caused in part from a childhood virus. A virus particle, known as a paramyxovirus nucleocapsid, has been identified within the bone cells of individuals with Paget’s disease. This virus particle is not found in normal bone. While this relationship has been identified, a clear connection between the virus and the cause of Paget’s disease is not known.

An estimated 15% of people who have Paget’s disease have a close family member who also has the condition. If one has a first degree relative with Paget’s disease, such as a parent, brother or sister, risk is elevated and a person is seven to eight times more likely to develop the condition.

The evidence that environmental factors may play a role in Paget’s disease is based on the fact that the number of people who are affected by the condition has fallen sharply over the last 50 years. If Paget’s disease was only caused by genetic mutations, the number of new cases that are recorded by the authorities each year would either stay relatively stable or would increase.

One suggested environmental factor is the measles virus. The virus may lay dormant for many years before being ‘re-activated’ and attacking the osteoclast cells, causing them to malfunction. Therefore, the fall in the number of cases of Paget’s disease could be because of a corresponding fall in the number of measles infections owing to the measles vaccination programmes.

Diagnosing Paget’s Disease

Diagnosis of Paget’s disease is made by physical examination, x-rays, and laboratory studies. The physical examination may show abnormalities of the skeletal shape or bone deformities. X-rays commonly show abnormalities of bone turnover, including areas of increased and areas of decreased bone deposition. Laboratory studies will invariably show an increased level of alkaline phosphatase, a byproduct of bone formation. Calcium levels within the body are usually normal.

What are the treatment options for Paget’s Disease?

In general, patients with Paget’s disease should receive 1000-1500 mg of calcium, adequate sunshine, and at least 400 units of vitamin D daily. This is especially important in patients being treated with bisphosphonates; however, taking oral bisphosphonates should be separated from taking calcium by at least two hours, because the calcium can inhibit the absorption of the bisphosphonate. Patients with a history of kidney stones should discuss calcium and vitamin D intake with their physicians. Both these Paget’s disease treatment medications prevent the weak parts of bone that cause deformity and are at high risk for being fractured.

Sometimes surgery is needed if there is a significant bone deformity or if there is a break in the bone. Fractures are most common in the femur (thigh bone) and tibia (shin bone), and are usually treated with an intramedullary rod, a rod that is inserted within the marrow cavity in the center of the bone. Unfortunately, fractures often take a long time to heal in patients with Paget’s disease because of the abnormalities in bone turnover.

Another common surgery in patients with Paget’s disease is called an osteotomy. In this procedure a wedge of bone is removed to correct a malalignment. This procedure 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 treatment is given before major changes have occurred in the affected bones. Treatment can control Paget’s disease and lessen symptoms but is not a cure.

Preventing Paget’s Disease

Paget’s Disease is unavoidable in most cases, however exercise is very important in maintaining skeletal health, avoiding weight gain, and maintaining joint mobility.

Since undue stress on affected bones should be avoided, patients should discuss any exercise program with their physician before beginning.

Sources: National Health Service (NHS), UK, The Mayo Clinic, Wikipedia, HHS (Department of Health and Human Services USA), NIH (National Institutes of Health, USA).