INTRODUCTION — Osteoporosis is characterized by a progressive decrease in bone density, causing bones to become brittle, weakened, and fracture easily. Osteoporosis and the fractures that result are a major public health concern; more than 1.3 million osteoporotic fractures occur annually in the United States. Early diagnosis of bone loss can reduce or eliminate the risk of fractures.
This topic review discusses the causes, risk factors, signs, and symptoms of osteoporosis, as well as the ways that it can be diagnosed. For information about ways to prevent and treat osteoporosis, see "Patient information: Osteoporosis prevention and treatment".
BONE METABOLISM — To maintain bone density and strength, the body needs a sufficient supply of calcium and phosphorus, normal production of hormones that help to regulate bone cell function (eg, the calcium-regulating hormones, parathyroid hormone, calcitriol, and calcitonin; thyroid hormone; glucocorticoids; the sex hormones estrogen and testosterone), and an adequate supply of vitamin D, which is essential for normal bone formation and calcium absorption.
Bone is constantly being turned over and replaced as a result of cells that break down and remove bone (osteoclasts) and cells that replace and rebuild bone (osteoblasts). The resorption and formation of bone are essential to repair tiny breaks (microfractures) and to "remodel" bone (ie, remove and replace bone) in response to stress, including injury.
Osteoporosis is the result of years of bone loss, due to a "mismatch" between bone formation and resorption. Osteoporosis may also be related to years of inadequate bone formation, especially during the teens and 20s, which are the most important years of bone building. When bone becomes abnormally thin (known as osteopenia) and porous, the risk of fracture increases. Osteopenia is
Cortical bone, the normally dense, compact bone that forms the outer part of skeletal structures, provides strength and protection. Trabecular bone is found inside the long bones, particularly at the ends, and helps to provide mechanical support, particularly within the vertebrae. In patients with osteoporosis, both cortical and trabecular bone may be affected (show figure 1).
The processes of bone resorption and formation vary with age. Although 95 to 100 percent of expected peak bone mass develops by the late teen years, the body continues to form more bone than it breaks down until approximately 30 years of age. Maximum bone density is attained between 20 years (hip) and 30 years of age (spine and forearm). Thereafter, bone mass is slowly lost in the spine and hip; the loss occurs more rapidly during perimenopause.
SIGNS AND SYMPTOMS — Osteoporosis usually causes no symptoms until a fracture occurs, but it can cause back pain or loss of height.
Vertebral fractures — Vertebrae are the bones that make up the spine, and vertebral fractures are the most common sign of osteoporosis. About two-thirds of these fractures occur without symptoms. In these cases, the fracture is found during a chest or abdominal x-ray done for other reasons. In some patients, vertebral fractures may lead to a sudden onset of back pain, usually when performing routine activities, such as bending or lifting. This pain usually resolves over several weeks and is replaced by a chronic dull ache or pain. However, the pain may sometimes persist for many months. Successive compression or crush fractures, in which there is collapse of affected bone, may lead to increased curvature of the spine (thoracic kyphosis). As a result, there is typically an abnormal rounding of the upper back, known as a "dowager's hump," and loss of height (show figure 2). Due to vertebral fractures and associated height loss, the abdomen may be compressed, causing it to bulge forward. Such patients may note that their abdomens appear larger than before, their clothes no longer fit, and their waists seem to have "disappeared" even though they have not gained weight. Patients with multiple vertebral compression fractures may also have hip discomfort. The pain may be due to a decrease in the distance between the bottom of the rib cage and the uppermost portion of the pelvis. This change may also result in difficulty breathing or digestive abnormalities, such as constipation or an early feeling of fullness while eating.
Other fractures — Hip fractures are relatively common in patients with osteoporosis, affecting 15 percent of women and 5 percent of men by age 80. Such fractures are a major cause of disability in the elderly and increase the risk of death, although conditions other than the fracture (such as surgical complications) may be responsible for this increase.
Osteoporosis may also lead to fractures near the wrist in the lower end of the radius (the bone on the thumb side of the forearm), causing backward displacement of the wrist and hand. This type of break is known as a Colles' fracture, and often results when the hand is outstretched to stop a fall.
CAUSES — As mentioned above, osteoporosis results from either accelerated bone loss or inadequate bone formation. The imbalance between the rate of new bone formation and breakdown may occur due to several underlying conditions, including the following:
Menopause-related loss of estrogen — Estrogen is a hormone that plays an important role in regulating bone formation. The rate of bone loss increases soon after the menopause, particularly in trabecular bone; this increased rate of loss lasts for approximately 10 years. At this point, the rate of bone loss slows to near the premenopausal rate, but the premenopausal rate of bone formation is absent.
Hyperthyroidism — Hyperthyroidism is a condition in which the thyroid gland is overactive in its production of thyroid hormones. It is associated with increased bone turnover, potentially leading to bone loss. (See "Patient information: Hyperthyroidism").
Hyperparathyroidism — Hyperparathyroidism refers to overactivity of the parathyroid glands. These glands produce parathyroid hormone, which helps to regulate calcium concentrations in the body. Increased secretion of parathyroid hormone increases the removal of calcium from bone, raising blood calcium levels (hypercalcemia) and potentially leading to osteoporosis. (See "Patient information: Primary hyperparathyroidism").
Age-related bone loss — This may result from decreased calcium absorption, which typically begins in the fourth or fifth decade of life. It is associated with a slow loss of cortical and trabecular bone in both women and men.
Hypogonadism — Hypogonadism is a decrease in activity of the ovaries or testes resulting in low amounts of estrogen or testosterone, respectively. This may be a result of aging, but it can also occur in younger men and women due to medications that cause hypogonadism (eg, chemotherapy agents), block estrogen synthesis (aromatase inhibitors), or induce testosterone/estrogen deficiency (GnRH agonists). It may also occur as a result of low body weight, excessive exercise, or pituitary abnormalities.
Men who have low or absent levels of the hormone testosterone are at increased risk of osteoporosis, and women who have a low level of estrogen are also at risk. Symptoms of hypogonadism in men include a decreased sexual drive (libido) or impotence. In young women, signs of hypogonadism include loss of menstrual periods, which may or may not be associated with hot flashes, night sweats, or vaginal dryness.
Medications — Prolonged therapy with certain medications, including glucocorticoids (also called corticosteroids), heparin, certain medications for seizure disorders (eg, phenytoin, carbamazepine, primidone, and phenobarbital), cyclosporine, medroxyprogesterone acetate and vitamin A may result in accelerated bone resorption as well as slowed bone formation, leading to bone loss.
Pregnancy and breastfeeding — Bone loss occurs during pregnancy and breastfeeding, although the loss is temporary and has no long term effect on a woman's bone density. In women who become pregnant and breastfeed, there is no increased risk of fracture after menopause. Using a calcium supplement while breastfeeding has no effect on the amount of bone lost.
Vitamin B12 deficiency — Vitamin B12 deficiency (also known as pernicious anemia) appears to increase the risk of osteoporosis, which can lead to an increased risk of hip and spine fractures.
RISK FACTORS FOR FRACTURE — Several factors are associated with an increased risk of osteoporotic fractures, including the following:
Age — In people aged 90 years or more, approximately one-third of women and 15 percent of men will have a hip fracture.
Sex — Osteoporosis is a serious problem in men, although women are affected more commonly. Women have a lower average peak bone mass and lose more bone after menopause. About 30 percent of women over age 50 have osteoporosis, and this percentage increases with age.
Race — Whites have a considerably higher risk of hip fractures than blacks. Blacks generally have a higher peak bone mass and a lower rate of bone loss after menopause.
Falls — Repeated falling can be a significant problem for older people with osteoporosis. Over 90 percent of hip fractures occur after a fall. Certain factors contribute to the risk of falls, including poor vision, certain medications (eg, tranquilizers, some anxiety medications, sleeping pills), and neurologic disorders such as dementia (confusion).
Other factors — A number of other factors increase the risk of fractures, some of which include the following: Previous fracture between the ages of 20 and 50 years History of fracture in a first degree relative Cigarette smoking (men and women) Inflammatory bowel disease Celiac disease Cystic fibrosis Sedentary life style Drinking large amounts of caffeine Medications for anxiety or seizures Low body weight or weight loss Above average height Type 1 or 2 diabetes mellitus
DIAGNOSIS — Osteoporosis is diagnosed based upon the patient and family history, physical examination, laboratory studies, and bone mineral density (BMD) testing. It is important to exclude other conditions that can cause bone thinning (osteopenia), such as osteomalacia (softening and weakening of bone) as well as other potentially treatable conditions (eg, hyperparathyroidism, hyperthyroidism, kidney disease).
History and physical examination — During a medical history, a healthcare provider will ask about life events (pregnancies, age at first menstrual period and menopause), past or present medical conditions, medications, calcium intake, exercise, and alcohol/tobacco use.
The physical examination will include measurement of height and weight and may include laboratory tests. Such studies may include a complete blood count, measurement of calcium, phosphorus, vitamin D, bicarbonate, creatinine, and hormones such as thyroid-stimulating hormone (TSH). The testosterone level may be measured in men, particularly if the man has decreased libido or impotence. (See "Patient information: Sexual problems in men").
Bone density measurement — Measurement of bone mineral density is the most common method to determine if a person is at risk for or already has osteoporosis. The goal is to recognize people who are at risk before a fracture occurs. Several methods are available to measure bone density.
Dual x-ray absorptiometry (DXA) — DXA testing is the most popular method for measuring BMD because it provides precise measurements at important bone sites (eg, spine, hip, forearm) with minimal radiation.
During DXA, the patient lies on an examination table. An x-ray detector scans a bone region, and the amount of x-rays that pass through bone are measured and displayed as an image that is interpreted by a radiologist. The test causes no discomfort, and usually takes only 5 to 10 minutes. The bone mineral density is then compared with the normal range for the patient's sex and race.
Other Quantitative computerized tomography — This is a type of CT that provides accurate measures of bone density in the spine. Although this test may be a good alternative to DXA, it is seldom used because it is expensive, less precise for following measurements over time, and requires a higher radiation dose. Ultrasonography — Ultrasound can be used to measure the bone density of the heel. This may be useful to determine a person's fracture risk. However, it is used less frequently than DXA because there are no guidelines that use ultrasound measurements to diagnose osteoporosis or predict fracture risk. In areas that do not have access to DXA, ultrasound is an acceptable way to measure bone density.
We recommend DXA of the hip and spine because measurements at these sites are effective for predicting osteoporotic fracture at any site.
Interpreting BMD results — The World Health Organization (WHO) has defined normal bone density as a value within one standard deviation (SD) from average peak bone mass. Standard deviation is a statistical measure that defines how much a patient's result vary from the "average" young adult. Normal bone density — Bone density that is between 0 and 1 standard deviation below the mean is considered to be normal. This may be reported as a T-score of 0 to -1. Treatment is not usually recommended for people with normal bone density, although preventive measures (eg, calcium supplementation, weight-bearing exercise) are recommended to prevent osteopenia and osteoporosis. (See "Patient information: Osteoporosis prevention and treatment"). Osteopenia — Bone density that is between 1 and 2.5 standard deviations below the mean is called osteopenia. This may be reported as a T-score of -1 to -2.4. A person with osteopenia does not yet have osteoporosis, but is at risk to develop it if not treated. Osteoporosis — Osteoporosis is defined as BMD more than 2.5 standard deviations (SD) below the mean of normal young women. This is reported as a T-score of -2.5 or less. The lower the bone density, the greater the risk of fracture.
When to measure BMD — Bone density testing can be used to diagnose osteoporosis, as well as to screen for it. The National Osteoporosis Foundation has issued recommendations for bone density testing that primarily apply to white women after menopause. Bone density should be measured in women: Greater than 65 years of age Under age 65 who have one or more risk factors for osteoporotic fracture in addition to menopause.
In addition to the recommendations above, the International Society for Clinical Densitometry (ISCD) recommends bone density testing for men over 70 years of age and for adults (including premenopausal women): With fragility fracture (a bone fracture that occurs after a fall from standing height or less) With disease associated with low bone mass (Cushing's syndrome, hyperthyroidism, hyperparathyroidism, rheumatoid arthritis, gastrointestinal diseases associated with malabsorption) Taking drugs associated with low bone mass (glucocorticoids, GnRH agonists, some chemotherapy drugs)
PREVENTION AND TREATMENT — All women should be educated about the risk factors for osteoporotic fractures. A provider may recommend certain lifestyle changes that can help to reduce fracture risk, such as stopping smoking, limiting alcohol consumption, and participating in regular weight-bearing and muscle-strengthening exercises. A full discussion of osteoporosis prevention and treatment is available separately. (See "Patient information: Osteoporosis prevention and treatment").
WHERE TO GET MORE INFORMATION — Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two patients are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.
This discussion will be updated as needed every four months on our web site (www.patients.uptodate.com). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.
A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable. National Library of Medicine
(www.nlm.nih.gov/medlineplus/healthtopics.html)
Osteoporosis and Related Bone Diseases National Resource Center (ORBD-NRC)
Toll-free: (800) 624-BONE (2663)
TTY: (202) 466-4315
(www.osteo.org)
National Osteoporosis Foundation
Phone: (202) 223-2226
(www.nof.org)
International Society for Clinical Densitometry (ISCD)
(www.ISCD.org)
National Women's Health Resource Center (NWHRC)
Toll-free: (877) 986-9472
(www.healthywomen.org)
Osteoporosis Society of Canada
Phone: (416) 696-2663 x 294
(www.osteoporosis.ca/)
The Hormone Foundation
(www.hormone.org/public/osteoporosis.cfm, available in English, Spanish, French, Italian, German, and Portuguese)
[1-4]
Use of UpToDate is subject to the Subscription and License Agreement. REFERENCES 1. Johnell, O, Kanis, JA, Black, DM, et al. Associations between baseline risk factors and vertebral fracture risk in the Multiple Outcomes of Raloxifene Evaluation (MORE) Study. J Bone Miner Res 2004; 19:764.
2. Raisz, LG. Clinical practice. Screening for osteoporosis. N Engl J Med 2005; 353:164.
3. Marshall, D, Johnell, O, Wedel, H. Meta-analysis of how well measures of bone mineral density predict occurrence of osteoporotic fractures. BMJ 1996; 312:1254.
4. Bainbridge, KE, Sowers, MF, Crutchfield, M, et al. Natural history of bone loss over 6 years among premenopausal and early postmenopausal women. Am J Epidemiol 2002; 156:410.
No comments:
Post a Comment