Questions about Paget's disease (usually referenced in the medical literature as Paget disease) and osteoporosis come up over and over again. If I have osteoporosis, will I suffer the even more devastating consequences of Paget's disease? The reassuring answer is no. Here are the reasons why.
What is Paget's disease?
Paget's disease is a condition that leads to fractures of the bone. Understanding how Paget's disease relates to the much more common osteoporosis requires a little understanding of how bones repair themselves.
Healthy bone is constantly remodeling itself to heal microscopic microfractures that occur as stress and strain is applied to it. An unusual impact to the bone, or a change in exercise habits toward the more vigorous, will trigger a group of bone cells known as osteoclasts. These cells break down damaged or obsolete bone to make way for new, stronger bone. When they have dissolved old bone, another group of bone cells known as osteoblasts attaches tiny mineral crystals to a scaffold of collagen to create a new, strong structure. That's an oversimplification, but the picture is not far from the reality.
In osteoporosis, the osteoclasts and osteoblasts get out of sync. Maybe old bone is broken down too quickly, faster than new bone can be constructed. Maybe new bone is made too slowly, and can't keep up with bone recycling. Or maybe, as in senile osteoporosis, the bone remodeling process as a whole just can't keep up with the various kinds of metabolic and mechanical processes that break down bone. The result is bone that is fracture-prone.
In Paget's disease, the bone-destroying building and bone-rebuilding processes are not so much out of sync as they are out of proportion to the needs of healthy bone. First there is excessive resportion, the breakdown of bone. Then there is excessive remodeling, the rebuilding of bone, to compensate for it. Old bone is removed too quickly and replaced too quickly. The newly formed bone lacks the collagen framework that holds it together tightly. Bones get larger, filled with more blood vessels, and weaker than they should be. This makes them prone to still more fractures that repeat the process.
What are the differences between osteoporosis and Paget's disease?
That isn't where the differences between osteoporosis and Paget's disease stop. There are many more:
- Osteoporosis can occur in any bone, but is most common in the wrist, spine, and hip. Paget's disease can occur in any bone, but it is most common in the spine, pelvis, femur, sacrum, and skull, in order of descending frequency.
- Osteoporosis may occur in multiple bones. Paget's disease does not spread from bone to bone, but becomes progressively worse as it extends from a single site.
- In women, Paget disease may also affect the breast and vulva. Osteoporosis does not.
- Osteoporosis and Paget's disease both occur most frequently in the second half of life. Paget's disease, however, seems to be related to exposure tomeasles virus and respiratory syncytial virus in childhood, infections that may set up a hyperactivity reaction in osteoclasts.
- Osteoporosis and Paget's disease can both cause bone pain. However, Paget's disease can also cause a feverish feeling where bones are enlarged with excessive numbers of blood vessels. It can cause arthritis when it deforms joints. It can result in the formation of bony deformities when broken bones don't join back together after a fracture. It can cause neurological complications when excessive bone presses on nerves. Bone pain in Paget's disease usually does not respond to non-steroidal anti-inflammatory medications (NSAIDs) such as acetaminophen and ibuprofen. Paget's disease pain usually requires narcotics for effective control.
- Both osteoporosis and Paget's disease are sometimes treated with bisphosphonates (medications like Actonel, Fosamax, and Reclast) and salmon calcitonin. In both osteoporosis and Paget's disease, the success of bisphosphonates is measured by laboratory testing of C-telopeptide or N-telopeptide. (Sometimes in Paget's disease the doctor will order labs to measure BSAP, a bone breakdown marker, or deoxypyridinoline.) Unlike osteoporosis, Paget's disease is not treated with medications that replace or modify the bones' response to estrogen.
- Both osteoporosis patients and Paget's disease are encouraged to take at calcium and vitamin D supplements.
- Paget's disease can cause loss of site when bony growths interfere with the optic nerve.
- Paget's disease can cause kidney stones as the osteoclasts pump too much calcium out of bone and into the bloodstream, where it circulates to be excreted with urine.
- Osteoporosis does not lead to cancer. Paget's disease can lead to bone sarcoma, which can be deadly.
It is possible for people who have Paget's disease also to have primary or secondary osteoporosis. About 16 percent of Paget's disease patients do. However, it is rare for people who have primary or secondary osteoporosis also to have Paget's disease. The risk of being diagnosed with Paget's disease after being diagnosed with osteoporosis is only about 0.5 to 0.9 percent.