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Paget's disease of bone affects 5 - 10% of the elderly male population
and is about half as common in women. Its cause remains a puzzle.
Paget's disease of bone has a higher incidence in some families
than in others. Clear statistics from around the world strongly
suggest that, during the last century, it has become less common
and less severe.
What is Paget's Disease?
It is a benign overgrowth of regions of bone. Classically, a number
of bones in the skeleton became involved, but in recent times patients
seem to present with a milder form of the disease often affecting
only a single site.
Normally the skeleton is maintained by a balance between slow breakdown
and formation of bone. The cell involved in bone breakdown, called
the osteoclast, is derived from the immune system. The bone forming
cells, called osteoblasts, are related to the cells that produce
fibrous tissue and also fat. In the region affected by Paget's disease,
the osteoclasts increase in number, size and activity, leading to
a zone of rarefaction. The osteoblasts nearby react to produce more
bone which leads to an overgrowth of bone tissue.
The new bone that is laid down is abnormal in several respects.
Its structure is disorganized and it does not go on to remodel to
normal bone. It usually has many small blood vessels. Overall, the
bone is bulky and irregular and, at the functional level, it is
weak. On x-ray the bone texture reflects these changes, with an
early stage (which may last for years) in which a zone of translucency,
typically in the marrow space, spreads within the affected bone,
to be followed gradually by the denser disorganized new bone.
Any bone in the body can be affected and often spread occurs across
joints to the adjacent bone. Common sites are the pelvis or the
long bones of the legs, bearing most of the weight of the body,
or the skull.
Consequences
There are three typical consequences. The weak bone is continually
remodeling and gradually distorts under load, as though the bone
has been bent. A fracture may occur with only minimal overload.
Secondly, the bony enlargement near joints leads to distortion of
the joint surface, causing a secondary osteoarthritis. Specifically
in the skull, the bony thickening may lead to deafness, either from
involvement of the hearing ossicles of the middle ear, or compression
of the nerves. Finally, the disorder may be associated with low
grade discomfort in the affected area. Rarely, malignant change
can develop, usually heralded by evolving localized pain.
Causes
The cause remains unknown.
Since Paget's disease has an apparent clustering in some families,
the search for an abnormal gene has been energetically undertaken.
Treatment
Treatment is with the bisphosphonate group of drugs. These inactivate
the bone-resorbing cells. Unfortunately, these drugs do not reverse
the existing distortion of the bone, though it is believed they
strengthen it.
Monitoring
The best measure of Pagetic activity remains the simple blood level
of alkaline phosphatase, a product of osteoblasts. An attempt should
be made to get this into the normal range. However, with the many
cases of single bone involvement, patients may present with an apparently
normal alkaline phosphatase level. In those cases, it is usually
necessary to measure the bone specific alkaline phosphatase. If
severe, localized pain develops, early radiology is required to
rule out the rare possibility of malignant change.
This information is part of an article written by:
Dr. M. Cochran
Endocrine Bone & Menopause Centre
(endo@endocrine.com.au)
2003
The information presented is not intended to replace the medical
advice of your doctor or health care provider. Arthritis SA recommends
that you consult your doctor about specific medical conditions.
Other information and resources available
from Arthritis SA
Paget's Fact Sheet
• Email advisors@arthritissa.org.au
(please include your postal address in email)
Paget's SA
Support Group
Click here "Branches & Support
Groups" for further information
Telephone Advisory Service
9.30am - 3.30pm, Mon - Fri
8379 5711 or country free call on 1800 011 041
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