Paget’s disease of bone causes affected bones to grow larger, thicker, and misshapen over time. The visible changes depend on which bones are involved, but the most recognizable signs include bowed legs, an enlarged skull, and a curved spine. Many people with Paget’s disease have no visible changes at all, especially early on, because the disease often affects bones hidden beneath muscle and tissue. When changes do become noticeable, they tend to develop slowly over years.
Where the Disease Shows Up Most
Paget’s disease doesn’t affect the entire skeleton. It targets specific bones, and those bones determine what you’ll actually see. In a large multicenter study, the most commonly affected sites were the pelvis (about 44%), the skull (44%), the spine (41%), and the thighbone (28%). The pelvis is the single most frequent location, but because it’s deep inside the body, pelvic involvement rarely produces visible changes on the outside. Skull and leg involvement are what create the most obvious outward differences.
Visible Changes in the Skull and Face
When Paget’s disease affects the skull, the bones gradually thicken and expand. Over time, this can noticeably increase head size. Hats that once fit become too tight. The forehead may appear more prominent, and the overall shape of the head can look broader or heavier than before.
In more advanced cases involving the facial bones, the upper and lower jaw can enlarge, creating a broadened facial appearance sometimes compared historically to a lion’s face. The jaw expansion can change tooth spacing, making dentures fit poorly or causing gaps between teeth. The bones around the sinuses and eye sockets can also thicken, which in severe cases changes the contour of the midface.
As skull bones grow inward, they can narrow the small channels where nerves pass through. This pressure on cranial nerves can cause facial numbness, difficulty with facial movement, or hearing loss if the bones around the inner ear are involved. Imaging in these cases shows the skull bones dramatically thickened, with the space between the inner and outer layers of the skull widened well beyond normal.
Leg Bowing and Limb Changes
The legs are where Paget’s disease is most visibly obvious. The thighbone and shinbone are both common sites, and because these bones bear the body’s weight, they gradually bend under the load as the disease softens and enlarges them. The result is a noticeable outward or forward bowing of one or both legs. The bowing develops slowly, sometimes over a decade or more, and tends to worsen without treatment.
This bowing isn’t just cosmetic. It changes your gait, puts abnormal stress on the knee and hip joints, and increases the risk of fractures. The affected leg may also look slightly larger in circumference than the unaffected side because the bone itself has expanded.
Warmth Over Affected Bones
One subtle but distinctive sign of Paget’s disease is that the skin overlying an affected bone feels noticeably warmer than the surrounding area. This happens because blood flow to the skin above the diseased bone increases significantly. Research has shown that blood vessels in the skin over Pagetic bone are already dilated, meaning they’re running at high capacity even at rest. In one study, blood flow in affected limbs measured roughly four times higher than in the same limb on the opposite side. If you or a doctor places a hand over an affected shinbone or skull, the warmth can be easy to feel.
Spinal Curvature and Height Loss
When Paget’s disease involves the vertebrae, the affected bones can flatten or widen, leading to increased curvature of the upper back (a stooped posture) or loss of height. Some people lose an inch or more over the course of the disease. The enlarged vertebrae can also press on the spinal cord or the nerves branching off from it, causing pain, tingling, or weakness in the legs. On imaging, an affected vertebra may appear denser and larger than its neighbors, sometimes described as an “ivory vertebra” because it looks strikingly white compared to normal bone.
What It Looks Like on X-Rays and Scans
Most people first learn they have Paget’s disease from an X-ray or blood test done for another reason. On X-rays, affected bones look distinctly abnormal in ways that change as the disease progresses. Early active disease can show dark areas where bone is being broken down faster than it’s being rebuilt. As the disease advances into its rebuilding phase, the bone appears thicker, denser, and expanded, with the outer shell (cortex) visibly widened. In many cases, you can see both destruction and overgrowth happening in the same bone at the same time.
In the skull, X-rays can show a patchy, mottled pattern of dense and less-dense areas sometimes described as a “cotton wool” appearance. This reflects the chaotic, disorganized way the bone has been remodeled.
Bone scans are particularly useful for mapping the full extent of the disease. In this type of imaging, a small amount of radioactive tracer is injected and collects wherever bone is actively turning over. In Paget’s disease, affected bones light up intensely compared to surrounding healthy bone, making it easy to identify every involved site in a single scan. The uptake is markedly increased across the entire affected bone, not just at the edges.
What the Bone Looks Like Under a Microscope
If a biopsy is taken, Paget’s bone has a characteristic “mosaic” pattern that pathologists can identify immediately. Normal bone is laid down in organized, parallel layers. Pagetic bone has been broken down and rebuilt so many times, in such a haphazard way, that the layers run in random directions, creating a jigsaw puzzle appearance. This disorganized structure is why the bone, despite being larger and denser than normal, is actually weaker and more prone to fracture.
How Blood Tests Reflect the Disease
Paget’s disease doesn’t have a visible “look” in blood work, but one marker runs consistently high: alkaline phosphatase, an enzyme released during bone formation. Normal levels typically fall between 38 and 113 U/L. In active Paget’s disease, levels climb above that range, sometimes modestly (around 150 U/L in mild cases) and sometimes dramatically in widespread disease. Doctors use this number both to confirm the diagnosis and to track whether treatment is working. A dropping alkaline phosphatase level generally means the abnormal bone turnover is slowing down.
Why Many Cases Go Unnoticed
Despite all these potential changes, most people with Paget’s disease never develop dramatic visible deformities. The disease is often limited to one or two bones, progresses slowly, and in many cases is caught incidentally on an X-ray or blood test before any outward change occurs. Bone pain, particularly a deep ache that worsens at night or with weight bearing, is frequently the first symptom rather than a visible change in shape. The classic bowed legs and enlarged skull represent advanced, long-standing disease that is less common today because of earlier detection and effective treatment that slows the abnormal bone remodeling.