Paget disease of bone is a chronic disorder of the skeleton in which areas of bone undergo abnormal turnover, resulting in areas of enlarged and softened bone.
Paget disease can affect any bone, but the most commonly affected bones are the pelvis, thighbone (femur), skull, shin (tibia), spine (vertebrae), collarbone (clavicle), and upper arm bone (humerus).
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. Many people have no symptoms.
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 (bone remodeling—see Osteoporosis) 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. The disorder tends to run in families, and recent information suggests that a group of genetic defects possibly contributes. Also, some evidence suggests that a virus is involved. However, there is no evidence that the disorder is contagious.
Overgrown bone may compress nerves and other structures passing through small openings. The spinal canal may become narrow and compress the spinal cord. Osteoarthritis (see Joint Disorders: Osteoarthritis (OA)) may develop in joints near the involved bone.
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 if subjected to surgery. The affected bone becomes cancerous in fewer than 1% of people who have Paget disease. People whose disease progresses to bone cancer (see Bone and Joint Tumors: Primary Cancerous Bone Tumors) usually develop an osteosarcoma.
High blood levels of calcium (hypercalcemia—see Electrolyte Balance: Hypercalcemia) occasionally occur in bedridden older people with Paget disease or in anyone with severe Paget disease who becomes immobilized or dehydrated. These high levels of calcium can result in many problems, such as high blood pressure, acute kidney injury, muscle weakness, constipation, and stones in the urinary tract.
In some people, the parathyroid gland becomes overactive, resulting in a need to consume more calcium. If too little calcium is consumed, low blood levels of calcium can occur, occasionally resulting in problems such as confusion, poor memory, and muscle aches and twitches.
Paget disease usually causes no symptoms, although 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. 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. The vertebrae may enlarge, weaken, and buckle, resulting in a loss of height and a hunched posture. Damaged vertebrae may pinch the nerves of the spinal cord, causing pain, numbness, tingling, weakness, or, very rarely, even paralysis in the legs. People may have bowing of the upper arm, thigh, or leg bones. People with bowed thighs or legs may take short, unsteady steps. Affected bones are more likely to break.
Paget disease is often discovered accidentally when x-rays or laboratory tests are performed for other reasons. Otherwise, the diagnosis may be suspected based on the symptoms and a physical examination. The diagnosis can be confirmed by x-rays showing abnormalities characteristic of Paget disease and by a laboratory test indicating elevated blood levels of alkaline phosphatase, an enzyme involved in bone cell formation. A bone scan (a radionuclide test 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 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.
Commonly used 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.
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:
The newer bisphosphonates (such as zoledronate) seem to slow the progression of Paget disease for a longer period of time.
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.
Doctors encourage weight bearing (such as standing and walking). Bed rest (except for sleeping at night) should be avoided, if possible, to prevent hypercalcemia. If severe hypercalcemia does develop, intravenous fluids and a drug called furosemide are given to increase the excretion of calcium.
Dietary intake of calcium and vitamin D (necessary for calcium absorption) should be sufficient to ensure that the incorporation of calcium into bone (bone mineralization) is adequate, because bone is being remodeled rapidly (see Biology of the Musculoskeletal System: Bones). Otherwise, poor bone mineralization (osteomalacia) may occur.
Last full review/revision August 2012 by Roy D. Altman, MD