Paget’s disease is a chronic bone disorder where the body’s normal process of breaking down and rebuilding bone goes haywire in specific areas, producing enlarged, misshapen, and weakened bones. It typically develops after age 55 and most often affects the spine, pelvis, leg bones, and skull. Global prevalence ranges from 1.5% to 8.3%, with the highest rates among people of European descent living in the United Kingdom, Australia, New Zealand, and North America. The condition is rare among Scandinavians, Africans, and Asians.
A completely separate condition called Paget’s disease of the breast also exists. It’s a rare form of breast cancer affecting the nipple and has no biological connection to the bone disease. This article focuses on Paget’s disease of bone.
What Happens Inside the Bone
Your bones are constantly being remodeled. Specialized cells called osteoclasts dissolve small amounts of old bone, and other cells called osteoblasts fill in new bone behind them. In Paget’s disease, the osteoclasts in one or more bones become wildly overactive. They grow larger than normal, contain more nuclei, and respond too aggressively to the chemical signals that normally regulate them. The result is excessive bone breakdown in patches.
The body tries to compensate by ramping up new bone formation, but the replacement bone is disorganized and structurally inferior. This represents the most exaggerated example of the coupling between bone-destroying and bone-building cells found anywhere in medicine. The new bone is often thicker and wider than normal yet paradoxically weaker, with a chaotic internal architecture instead of the orderly mineral pattern healthy bone relies on for strength.
Who Gets It and Why
Genetics play a meaningful role. Between 20% and 40% of people with a family history of Paget’s disease carry mutations in a gene called SQSTM1, which is involved in how cells recycle their internal components. Among people who develop the disease without a family history, about 5% to 10% still carry the same mutation. Researchers believe environmental triggers, possibly including viral exposure, interact with genetic susceptibility to set the disease in motion, but the exact combination remains unclear.
The condition is most common in the UK and among populations with British ancestry. It develops overwhelmingly in people over 50, with a typical onset in the late 50s, and is slightly more common in men.
Symptoms and Affected Areas
Many people with Paget’s disease have no symptoms at all. The condition is often discovered incidentally when blood tests or imaging are done for other reasons. When symptoms do appear, they depend on which bone is involved.
- Pelvis and spine: Deep, aching bone pain is the most common complaint. Spinal involvement can cause curvature and nerve compression.
- Leg bones (femur and tibia): The affected bone can bow outward over time, changing your gait and putting stress on nearby joints. Fractures become more likely because the disorganized bone is weaker than it appears on the outside.
- Skull: The skull may gradually enlarge, sometimes noticeably increasing hat size. Headaches are common. When the disease involves the temporal bone surrounding the inner ear, hearing loss can develop. Research on temporal bones from people with Paget’s disease shows this hearing loss comes from changes in bone density around the cochlea, the spiral structure of the inner ear, rather than from nerve compression. The altered bone dampens the finely tuned mechanics that transmit sound vibrations.
Arthritis in joints next to the affected bone is another frequent complication, because the misshapen bone changes how forces travel through the joint.
How It’s Diagnosed
A blood test measuring a marker of bone turnover called alkaline phosphatase is usually the first clue. In active Paget’s disease, levels are elevated because of the accelerated bone remodeling. The degree of elevation generally tracks with how much of the skeleton is involved.
X-rays reveal characteristic changes. In the early, active phase, a V-shaped or flame-shaped zone of bone destruction advances through the affected area. As the disease progresses into its mixed phase, you see a combination of bone loss alongside thickened outer bone walls and coarsened internal bone patterns. In the skull, the classic finding is a “cotton wool” appearance: fluffy, irregular patches of dense and less-dense bone scattered across the image. These imaging features are distinctive enough that additional testing is rarely needed, though a bone scan can help map all the sites involved throughout the skeleton.
Treatment and Long-Term Outlook
Not everyone with Paget’s disease needs treatment. If the condition is discovered incidentally and isn’t causing symptoms or threatening a critical area like the skull base or a weight-bearing bone, monitoring alone may be appropriate.
When treatment is warranted, a class of medications called bisphosphonates is the standard approach. The most effective option is a single intravenous infusion that takes about 15 minutes. This treatment works by slowing down the overactive bone-destroying cells, allowing the bone-building process to catch up with more organized, stronger bone. For most people, a single treatment produces a remission sustained for more than six years, and retreatment is seldom needed within five years. This makes it both convenient and cost-effective compared to older treatments that required daily pills for months.
Pain relief often follows within weeks to months of treatment as the frantic bone remodeling slows. Alkaline phosphatase levels in the blood drop toward normal, giving doctors a simple way to confirm the treatment is working.
Complications Worth Knowing About
The most serious, though uncommon, complication is malignant transformation. In about 0.7% of cases, Pagetic bone develops into a bone cancer called osteosarcoma. Warning signs include a sudden increase in pain, rapid swelling, or a fracture in a previously stable area of disease. This is rare enough that it shouldn’t cause alarm, but it’s the reason doctors continue to monitor people with Paget’s disease over time.
Other complications depend on location. Skull involvement can lead to progressive hearing loss that may not fully reverse with treatment, though slowing the disease can prevent further deterioration. Spinal disease can narrow the channels through which nerves travel, causing numbness, tingling, or weakness in the legs. Severely bowed leg bones alter walking mechanics and accelerate wear on the hip and knee joints, sometimes requiring joint replacement surgery independent of the Paget’s disease itself.
In very extensive disease affecting multiple bones, the heart has to work harder to supply blood to all the metabolically active bone tissue. This is rarely a problem unless the disease involves a large portion of the skeleton.