BONE DISORDERS AND OSTEOPOROSIS IN CD
Extraintestinal Complications: Bone Loss
Although bone seems as hard as a rock, it's actually living tissue. Throughout your life, old bone is removed and new bone is added. This is bone resorption and bone formation -- a process of continuous bone turnover known as bone remodeling.
If bone resorption and formation occurred at exactly the same pace, bone mass would remain the same. But this isn't the case. After age 35 or so, bone resorption outpaces formation and bone density begins to decline. Some loss of bone density is normal. Only when the process accelerates does osteoporosis -- a condition that literally means "porous bones" -- become a threat.
Considerable information points to osteoporosis as yet another extraintestinal complication of IBD. Recent evidence indicates that as many as 30-60 percent of IBD patients have low bone density. Although affected individuals may notice some back pain or a change in stature, there are generally no symptoms of this disorder until the bone has become weakened to the point that fractures occur. Bone fractures due to osteoporosis most commonly occur in the spine and hips. This is why screening tests for bone loss (bone density testing) and prophylactic measures to prevent bone loss are so important.
In addition to osteoporosis, other common bone abnormalities are osteopenia (low bone density) and osteomalacia (poor mineralization of bone). Although these abnormalities should not be overlooked in people with ulcerative colitis, they are more common in Crohn's disease. In fact, many individuals with Crohn's have osteoporosis at just the age when they should be at peak bone strength (age 20 for women and age 30 for men).
The Impact of Corticosteroids
Bone loss in IBD patients is due to both the inflammatory disease process and some of the medications (especially long-term use of corticosteroids) used to treat IBD. It is believed that 30-50 percent of people who take corticosteroids on a long-term basis develop osteoporosis, and the effects are cumulative. Your chances of developing osteoporosis increase depending on the dose and length of time that you are on these agents. One specific complication of corticosteroid therapy is osteonecrosis. This is caused by a loss of blood supply to a particular part of the body -- usually the wrists or hips -- resulting in bone cell death. Corticosteroid medications impair the formation of new bone by:
Decreasing the amount of calcium (an essential bone -- building mineral) absorbed from food
Increasing the excretion of calcium in the urine
Stimulating cells that break down bone
Reducing the production of estrogen, which contributes to strong bones
Diagnosis of bone loss is generally made with a special X-ray technology called dual-energy X-ray absorptiometry (DEXA). Results of the test -- which measures bone mineral density in the spine, hip, and other bones -- indicate the risk of suffering a bone fracture. A diagnosis of osteopenia (weak bones) doubles the risk of fracture; osteoporosis increases the risk by four or five times. It is recommended that all patients with Crohn's disease have a DEXA test as a baseline screening for early bone loss. Those with ulcerative colitis should be screened only if they have used steroids on a long-term basis.
Treatment of Osteoporosis
Corticosteroid-induced osteoporosis has no specific treatment but now the bisphosphonates, Actonel and Fosamax, have shown themselves to be helpful. However, preventive measures include reducing the controllable risk factors that contribute to bone loss -- such as cigarette smoking, lack of exercise, and excessive use of alcohol. (Other risk factors that can't be controlled include a positive family history of osteoporosis, menopause, age, and race -- with Caucasians and Asians at greater risk.) Eating a diet rich in calcium can also help avoid osteoporosis, as can the use of calcium supplements (1,500 mg per day).and vitamin D ( 400 u daily).
Extensive small bowel involvement with Crohn's disease may lead to vitamin D deficiency. This, in turn, may result in bone loss due both to reduced calcium absorption and to poor bone mineralization. That is why people who have undergone surgery to remove much of their small bowel are at increased risk of developing osteoporosis. The intestine that remains may not be adequate to absorb necessary quantities of calcium and vitamin D, which is a key ingredient for the absorption of calcium. In fact, if you don't get enough natural exposure to sunlight, which works to synthesize vitamin D in the skin, then dietary sources of the vitamin are essential. These include fortified milk, fish oils, and liver. If you already have osteoporosis, you should take 400 units daily of supplemental vitamin D, which can be found in many multivitamins.
Although they will not stop further bone loss once it has begun, both calcium and vitamin D supplements are safe and should not interfere with any medications you might be taking for IBD. Reducing steroid use (under your doctor's supervision) may help to minimize further bone loss. Hormone replacement therapy also appears to halt bone loss in postmenopausal women with IBD.
The Role of Inflammation in Bone Loss
It is not only long-term steroid use and small bowel surgery that may affect bone loss. The inflammation itself that marks Crohn's disease seems to play an important part in the breakdown and formation of bone. Investigators reached that conclusion after noting that many people with Crohn's who never had bowel surgery or received steroid therapy developed osteopenia or osteoporosis. The reasons are still not clear, but it appears that the answer may lie with cytokines, special proteins whose balance is disrupted in Crohn's disease. This disruption may well disturb the entire process of bone remodeling. It also appears that people with more active forms of Crohn's may be at increased risk of developing osteoporosis because their cytokine activity is greater. The cytokine connection might also explain why people with ulcerative colitis suffer less bone loss than those with Crohn's disease. Although the two diseases have many similarities, they do differ when it comes to cytokine balance. Even people who have had ulcerative colitis for years may still enjoy good bone health. Those who do show evidence of bone loss tend to be individuals who have used corticosteroids for some time.
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