Osteopetrosis and Paget’s Bone Disorders
One of our members asked a very interesting question on our Q&A board, also called (Ask a Question), about having high bone density, and how her Doctor was concerned about her above than average scores. Since we rarely get this question, I thought we'd discuss bone disorders that can cause an excess build up of bone. Normally we hear about low bone density, as we see in osteoporosis or osteopenia; however there are other metabolic bone disorders that are of importance to many.
Even though high bone density disorders are different than low, most of these disorders are treated similarly to osteoporosis, with often the same medications.
The World Health Organizations (WHO) definition on bone mineral density is as follows:
Normal Bone Density: Any score above -1.0
Osteopenia: Any score between -1.0 and -2.5
Osteoporosis: Any score at or below -2.5
The above scores tell us about normal, osteopenia and osteoporotic scores; however the other diseases of high bone density are discussed below.
Here are two of the metabolic bone disorders that can cause an excessively high bone density score, which would be a score above -1.0. There are other disorders that can cause this high bone density, but we'll limit the discussion to two of the most prevalent.
According to Dr. Carolino et al. from Saint Mary Hospital, Hoboken, New Jersey, "Osteopetrosis is a rare bone disease that may present in one of three distinct forms Osteopetrosis tarda, the most benign form, presents in adulthood and is often diagnosed incidentally on routine radiographs, whereas the two more malignant variants, osteopetrosis congenita and marble bone disease, present in infancy and childhood. In all three forms, the main features are pathologic alteration of osteoclastic bone resorption and thickening of cortical and lamellar bones ."
Causes of Osteopetrosis:
The causes of all forms of osteopetrosis are a failure of the mechanism involved in osteoclastic bone resorption. Osteopetrosis results in hardened, deformed and overly dense bones.
Treatment for Osteopetrosis:
Osteopetrosis tarda rarely requires treatment unless there are surgical or medical complications to repair degenerative joint disease.
Osteopetrosis congenita is managed with a bone marrow transplant due to failure of the patients' bone marrow.
Marble bone disease is treated with alkaline therapy. The more severe forms of osteopetrosis can cause mental retardation and failure to thrive.
According to the Merck Manual "Paget's disease is a rare bone disorder in which the cells that help build and destroy bone, go into overdrive, resulting in enlarged weakened bone. The Merck Manual states that this disease is usually found incidentally when looking at x-rays. The areas most commonly affected are the spine, pelvis and long bones of the arms and legs. The bone becomes larger and appears denser, but it is actually not as strong as regular bone ."
Causes of Paget's Disease:
In Paget's disease, both osteoclast's and osteoblast's become over active and produce bone that is enlarged, but also abnormally weak.
Treatment for Paget's:
Due to the enlargement of bone and possible nerve impingement, pain medications are given, like nonsteriodal anti-imflammatory (NSAIDs) and other analgesics like acetaminophen. Prognosis is generally good unless the patient develops bone cancer. Intravenous bisphosphonates are generally used for treatment for pain, prior to orthopedic surgery, to prevent arthritis, to slow weakness and deformity, and to reverse the elevation of alkaline phosphatase which occurs in these individuals. Bisphosphonates are also used for the associated hearing loss, bone deformity and to reduce bleeding during surgery.
Bed rest should be avoided in those with Paget's, except at night, to prevent hypercalcemia (high serum calcium).
Hopefully this explanation on two other types of metabolic bone disorders will help with those dealing with this type of bone disease which is different than osteoporosis.
- American Academy of Family Physicians Osteopetrosis March 15, 2008 Carolino et al. http://www.aafp.org/afp/980315ap/carolino.html
- Merck Manual, Paget's Disease of the Bone December 2007: Roy D. Altman MD http://www.merckmanuals.com/home/sec05/ch061/ch061a.html