The breakdown and formation of bone increase, resulting in bones that are thicker, but weaker, than normal.
Symptoms may be absent or may include bone pain, bone deformity, arthritis, and painful nerve compression.
X-rays show the bone abnormalities.
Pain and complications are treated, and bisphosphonates may be given.
Paget disease can affect any bone, but the most commonly affected bones are the pelvis, thighbone (femur), and skull. The shin (tibia), spine (vertebrae), collarbone (clavicle), and upper arm bone (humerus) are affected less commonly.
Paget disease rarely occurs in people younger than 40. In the United States, about 1% of people older than 40 have the disorder, and the prevalence increases with age. However, the prevalence of the disease seems to be decreasing. Men are 50% more likely than women to develop it. Paget disease is more common in Europe (excluding Scandinavia), Australia, and New Zealand.
Normally, cells that break down old bone (osteoclasts) and cells that form new bone (osteoblasts) work in balance to maintain bone structure and integrity. In Paget disease, both osteoclasts and osteoblasts become overactive in some areas of bone, and the rate at which bone is broken down and rebuilt (called bone remodeling) in these areas increases tremendously. The overactive areas enlarge but, despite being large, are structurally abnormal and weak.
The cause of Paget disease is unknown in most people. The disorder tends to run in families. Specific, identified gene abnormalities contribute in about 10% of people who have Paget disease, and other genetic abnormalities probably contribute in others. Also, some evidence suggests that a virus is involved. However, there is no evidence that the disorder is contagious.
The most common complication of Paget disease of bone is
Osteoarthritis (a joint disorder)
Osteoarthritis develops in up to 50% of people and may develop in joints near the involved bone.
Fractures tend to occur more easily than normal at involved bones because these bones are weakened by Paget disease. Such fractures are called pathologic fractures.
Overgrown bone may compress nerves and other structures passing through small openings. The spinal canal may become narrow and compress the spinal cord.
Rarely, heart failure develops because the increased blood flow through the affected bone puts extra stress on the heart. Because blood flow through affected bones is unusually high, those bones may bleed excessively during surgery. The affected bone becomes cancerous in up to 1% of people who have Paget disease. People whose disease progresses to bone cancer usually develop an osteosarcoma (a cancerous bone tumor).
High blood levels of calcium (hypercalcemia) may very rarely occur in bedridden people with Paget disease.
Paget disease usually causes no symptoms. However, bone pain, bone enlargement, or bone deformity may occur. Bone pain may be deep, aching, and occasionally severe and may worsen at night. The enlarging bones may compress nerves, causing more pain. If osteoarthritis occurs, joints become painful and stiff.
Other symptoms vary depending on which bones are affected.
The skull may enlarge, and the brow and forehead may look more prominent (called frontal bossing). A person may notice this enlargement when a larger hat is needed. Enlarged skull bones may damage the inner ear (cochlea), which can cause hearing loss, and dizziness. The enlarged skull bones can compress nerves, which causes headaches. The veins on the scalp may bulge, possibly because of the increased blood flow through the skull bones.
Bones the upper arm, thigh, or calf may appear bowed and are more likely to break because the bone is weakened by Paget disease. The vertebrae may enlarge, collapse, or both because bones affected by Paget disease are weak. Weakened vertebrae could result in a loss of height, a hunched posture, or pinching of the nerves of the spinal cord, causing pain, numbness, or weakness.
Paget disease is often discovered accidentally when x-rays or laboratory tests are done for other reasons. Otherwise, the diagnosis of Paget disease may be suspected based on the symptoms and a physical examination.
The diagnosis of Paget disease of bone can be confirmed by x-rays showing abnormalities characteristic of Paget disease and by a laboratory test to determine blood levels of alkaline phosphatase (an enzyme involved in bone formation), calcium, and phosphate.
A bone scan (a radionuclide scan using technetium) shows which bones are affected.
The prognosis for people with Paget disease is most often very good. However, the few people who develop bone cancer have a poor prognosis. People who develop other rare complications, such as heart failure or compression of the spinal cord, may also have a poor prognosis, unless treatment of these complications is timely and successful.
A person who has Paget disease needs treatment if the symptoms cause discomfort or if there is a significant risk or suggestion of complications, such as hearing loss, osteoarthritis, and deformity. People who do not have symptoms may not need any treatment.
Commonly used pain relievers (analgesics) such as acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs) help reduce bone pain. If one leg becomes bowed and shortened, heel lifts can help make walking easier. Sometimes surgery is needed to relieve pinched nerves or to replace a joint that has become arthritic from Paget disease.
Bisphosphonates are drugs that inhibit bone turnover. One of several bisphosphonates—alendronate, etidronate, pamidronate, risedronate, tiludronate, or zoledronate—can be used to slow the progression of Paget disease. Except for pamidronate and zoledronate, which are usually given by vein (intravenously), these drugs are given by mouth. These drugs are given for the following:
Before orthopedic surgery to prevent or reduce bleeding during surgery
To treat bone pain caused by Paget disease
To prevent or slow the progression of complications (such as hearing loss, bone deformity, arthritis, weakness, or paralysis), especially in people who cannot have surgery
To people with a blood level of alkaline phosphatase twice the normal level or higher
Calcitonin is occasionally injected under the skin or into muscle. It is not as effective as the bisphosphonates and is used only when the other drugs cannot be given. Denosumab may be another alternative for people who cannot take bisphosphonates.
Doctors encourage weight bearing (such as standing and walking). Excessive bed rest (except for sleeping at night) should be avoided, if possible, to prevent hypercalcemia.
Because bone is being remodeled rapidly, people should consume adequate amounts of calcium and vitamin D in their diet. Vitamin D helps the body absorb calcium and add it to bone (a process called bone mineralization). Vitamin D and calcium supplements are often needed. Otherwise, poor bone mineralization and bone weakening (osteomalacia) may occur.