Paget's Disease.
Last updated Monday, December 27, 2004
Causes and effectsCauses The cause of Paget's disease is unknown. One of the most accepted
theories points to an early viral infection of the bone. It is thought
that this infection lies inactive for many years, only to surface later
in life as Paget's disease.Effects To understand what happens in Paget's disease, it is helpful to
understand the difference between normal bone cell activity and Pagetic
bone cell activity. Bone is active and living tissue that constantly is
being remodeled in a three-stage process. First, old bone is resorbed
(broken down) by cells called osteoclasts to make way for new bone.
Next, cells called osteoblasts lay down an orderly framework for new
bony tissue. Finally, the bone hardens when calcium is added to the
framework laid down by the osteoblasts.
Normal bone cell activity is a very controlled process that is
necessary for bone development and repair throughout life. The bone
turnover process slows somewhat after puberty and continues at a slower
rate through adult life. (This is why an older person's bones break
more easily.)
Bone affected by Paget's disease is broken down faster than usual.
Consequently, new bone formation increases. Because the new bone forms
so rapidly, its structure becomes jumbled and disorganized. Extra blood
vessels appear, and the new formation becomes bulky and somewhat softer
than normal bone. This can result in joints near the affected area
developing arthritis.
Because the bones are weaker than normal, they may break or fracture
more easily. The thigh or leg can become bowed. If the vertebrae (bones
of the spine) are involved, they may collapse, making the spine curve
forward.
A person may experience other forms of discomfort as well. The
increased flow of blood through the bone may cause a feeling of warmth
over the affected areas. Thickened bones in some locations can pinch
nerves. For example, pinched nerves in the spine may cause sciatica, a
syndrome of radiating pain from the back into the buttocks and down the
legs. Paget's disease of the bones inside the ears also can cause
ringing or a decrease in hearing.
Eventually, the rapid bone breakdown and disorganized bone formation
slows down, and Paget's disease appears to "burn out." Symptoms may
come and go. However, any bone enlargement or bowing that has occurred
will remain.
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