Paget's disease of bone was first described by Sir James Paget in 1846. It is a rare disease affecting only 2-3 percent of the population over 60 years. It is slightly more common in men.
To understand the disease better, you need to understand the following terms:
Bone remodelling: This refers to the normal continuous process in our bones, in which bony tissue is broken down or resorped by osteoclasts, followed by the formation of new well-structured bony tissue by the osteoblasts.
Osteoclasts: Those cells in the bone which secrete very strong enzymes that break down and remove/absorb bony tissue.
Osteoblasts: The "b" in osteoblast reminds us of the building function of this cell. Osteoblasts secrete bony tissue that forms a strong matrix which becomes ossified (calcified) to form the rigid and strong bones in our body.
Bisphosph onates: The group of drugs that inhibits bone resorption by inhibiting the osteoclast cells.
What is Paget's disease?
It is a localised disease where there is an increase in bone resorption followed by abundant new bone formation. This newly formed bone has a very rich blood supply and a weak structure, leading to bony deformities and easy fracturing of the bone. These deformities of the bone and destruction of bony architecture around joints leads to early degeneration of joints. Interestingly, the Paramyxo virus (causing measles) has been implicated as a causative factor.
The majority of patients have no symptoms. If they have any, it is usually localised bone pain. Proposed reasons for the pain include increased blood flow, the pressure effect of new volume bone, or pain from joints (degenerative arthritis).
Some other symptoms that could present in more advanced disease are generally a result of bone overgrowth and the resulting pressure effects. In the spine, the pressure on the spinal cord or the spinal nerve roots could lead to severe pain in the arms or legs. Overgrowth of the skull can lead to deformities of the head and even deafness, if the hearing nerve gets compressed in its bony tunnel. In some cases severe headaches are caused by cranial nerves that get compressed.
More often a patient will present with a pathological fracture through the area of affected bone, caused by minimal impact which would otherwise not cause a fracture in normal bone.
Suspicion of the disease is raised with abnormal X-rays once a painful limb is viewed radiographically. A bone scan is a more sensitive test to diagnose pagetic bone lesions. The bone scan looks at the whole body and radio-isotopes shows a hot spot in areas where new bone is formed. Serum (referring to the blood) alkaline phosphatase is an enzyme that is released when bone is broken down and could be measured by a simple blood test. It correlates well with the extent of skeletal involvement. Although it is sensitive to correlate the extent of disease, it is not specific for Paget's disease, and could be raised in many other conditions like some liver conditions.
Most patients will not require any treatment other than normal anti-inflammatory tablets. In more severe cases like severe bone pain and neurological involvement, special therapy will be introduced. The mainstay of treatment remains drug therapy. The most common and first line of treatment is bisphosphonates, the group of drugs that inhibits bone resorption. A human hormone called calcitonin, which too inhibits bone resorption, may also be used.
The prognosis is generally good and the course of the disease is well controlled by drug therapy. Most patients will go into remission (bringing disease under control) but might suffer the complications of the poor-quality bone (like pathological fractures). In less than 1 percent of people suffering from Paget's, a cancer lesion can form.
Can Paget's be prevented?
It is a rare disease and no preventative measures have been identified.