Osteoporosis Diagnosis

  • Diagnosis

    Osteoporosis is the loss of bone density and strength Figure 01. A normal skeleton is made up of two major types of bone. One type, called cortical bone, is the dense, stiff bone that is the major component of the long bones of the legs and arms and other sites. Another type of bone, called trabecular bone (or “spongy” bone), occurs in areas such as the spine, hips, heels, and wrists, where flexibility and shock absorption are required. Trabecular bone contains many small holes (pores) through which blood circulates. Within these small pores, special cells called osteoclasts break down bone, and other special cells called osteoblasts build bone back up.

    The constant process of breakdown and re-formation is called remodeling. One cycle of remodeling takes up to six months. In fact, your entire skeleton is slowly replaced by remodeling every four to five years. Osteoporosis happens when osteoclasts break down bone more quickly than the osteoblasts form new bone. When this happens, your bones will lose strength and density. Trabecular bone loses density more readily than cortical bone.

    Early bone loss is just thinning of the bone around the already porous areas (osteopenia) Figure 02. At this early stage, bone loss may be fully reversible. If the process of bone loss is not reversed, however, it may eventually lead to severe osteoporosis. Osteoporotic bone contains much larger holes connected only by thin strips of weakened bone. This weakened bone is less dense, and is much more prone to fractures. Sites containing more spongy (trabecular) bone tend to fracture first, which is why hip, spine, and wrist fractures are more common than fractures at other sites. People with more severe osteoporosis have a greater risk of fracturing the ribs and the long bones of the arms and legs.

    Click to enlarge: Scanning electron micrograph of A) normal bone density and B) decreased bone density characteristic of osteoporosis

    Figure 01. Scanning electron micrograph of A) normal bone density and B) decreased bone density characteristic of osteoporosis

    Click to enlarge: Fracture sites in osteoporosis

    Figure 02. Fracture sites in osteoporosis

    As you age, your bones break down faster than they can build back up. The primary cause of osteoporosis is increasing age. Most women reach their maximum bone density by the age of 35—most men reach their maximum bone density by age 40. After you reach your peak bone density, your bone mass is maintained by a process whereby cells break down and re-form bone (remodeling). As you get older, however, your bones break down more quickly than they re-form. Therefore, your bones become thinner and more likely to break. Age-related losses of balance and muscle strength also increase your risk of falling and breaking a bone.

    Poor nutrition and lack of physical activity contribute to decreased bone density. It is important to consume calcium and vitamin D during adolescence and young adulthood. During this time your bones are still building mass, and calcium and vitamin D help to make them as strong as possible. It is also important to get regular physical exercise during this time; especially weight-bearing exercise.

    A poor diet and a sedentary lifestyle can hinder bone-building and contribute to brittle bones in later age. Drinking caffeine and soda on a regular basis, in particular, is thought to increase the rate of calcium loss from bones. This is particularly disturbing since many young people now drink soda and coffee instead of milk.

    It remains important to get exercise and consume calcium and vitamin D as you age to slow bone loss.

    Osteoporosis can occur without any symptoms Figure 03. You may not realize that your bones are becoming brittle until you get a fracture. Even regular x-rays cannot detect osteoporosis until you have lost more than 20% of your bone density.

    There are, however, some late signs of osteoporosis. A collapsed bone in your back (vertebra), for example, may cause severe back pain, loss of height, or a stooped posture (kyphosis) Figure 03. If you have lost more than 1½ inches of height since the age of 35, you are at increased risk for osteoporosis.

    Click to enlarge: Stooped posture (kyphosis)

    Figure 03. Stooped posture (kyphosis)

    Women are at a greater risk for osteoporosis than men Table 01. One out of two women and one out of eight men will break a bone because of osteoporosis after the age of 50. Women have a greater risk of osteoporosis because they have bones that are smaller and less dense than those of men. In addition, women tend to participate in fewer weight-bearing activities, and also tend to lose more bone mass than men. Women who have irregular menstrual cycles or no menstrual periods (amenorrhea) and women who have gone through menopause have a greater risk of osteoporosis. During the years just before and after menopause, women can lose about 20% of their bone mass.

    Low estrogen levels contribute to brittle bones. Estrogen helps prevent bone breakdown, but doesn't build bone. Therefore, if you have low estrogen levels, you may experience bone loss that is not replaced, even if your estrogen levels return to normal. Estrogen-related bone loss usually tends to occur earliest in the spine, with the hip and wrist losing bone somewhat later on.

    Some female athletes stop having their periods (amenorrhea) because the physical exertion changes their levels of reproductive hormones. These women are at risk for osteoporosis because their lack of estrogen causes them to lose bone mass. They may experience stress fractures that are very difficult to treat. This risk does not decrease if they exercise less or take calcium supplements.

    Osteoporosis isn't just a disease of the very old. Some women may lose half their bone mass by age 65 because of prematurely low estrogen levels.

    Young women with eating disorders (such as anorexia nervosa) are at risk for dramatic bone loss and stress fractures.

    If you are close to or have reached menopause, you are at an increased risk for having osteoporosis. During the time around menopause, some women lose bone as they begin to skip periods and have other menopausal symptoms. Some may have as much as 50% bone loss during the five to seven years before their periods stop and true menopause begins. Women who have reached menopause are at a particular risk for osteoporosis as their estrogen levels further decline.

    If you are a woman who has had her uterus removed (hysterectomy), you have a greater risk of osteoporosis.

    A total hysterectomy at any age results in rapid bone loss. Even when both ovaries remain following a partial hysterectomy, there is usually a significant decline in estrogen production following removal of the uterus that results in menopause and increased bone loss in about five to eight years.

    Osteoporosis from hormone loss also happens to men. Men who have low testosterone levels have a much higher risk for osteoporosis than other men. Osteoporosis related to low testosterone levels has a similar pattern to osteoporosis in women, and can cause significant bone loss in the spine and hip. Low testosterone levels can occur in men at any age; a decrease in sexual function and hair loss are the most common symptoms. All men over the age of 60 experience a decline in testosterone levels. Men who are treated for prostate cancer have a particularly high risk of osteoporosis.

    Of the men who have osteoporosis, 20% have a type known as "idiopathic," a type that has no cause. Idiopathic osteoporosis can occur at any age. As a result, men who have major fractures or fractures with very little trauma, or who have curvature of the upper spine (kyphosis) or unexplained height loss should be screened for osteoporosis.

    Insufficient vitamin D intake increases your risk of osteoporosis and decreases response to any osteoporosis treatment plan. Adequate levels of vitamin D are required in order to absorb calcium and to build bone. It is estimated that more than 70% of the population in the northern half of the U.S. are vitamin D-deficient. This significant bone loss is directly related to inadequate levels of vitamin D and sun exposure. This is true for all age groups, but is even more severe in the elderly. In addition, after age 50, there is a progressive decline in the absorption, metabolism, and effectiveness of vitamin D in both men and women. After about age 50 it is essentially impossible to get enough vitamin D from sun exposure alone. Vitamin D is not readily available in the diet, so supplements are usually required.

    Insufficient calcium intake increases your risk of osteoporosis and decreases your response to any osteoporosis treatment plan. Calcium is required to build and maintain bone density at all ages. After the age of about 50, your ability to absorb calcium decreases, which is often made worse if you don't get enough vitamin D. As a result, you should increase your intake of calcium after age 50. However, you should take your calcium in several smaller doses to optimize absorption.

    Having a small-boned frame or being tall increases your risk for osteoporosis. There is a direct relationship between increased height combined with low body weight and osteoporosis in both men and women. In women, body weight of less than 128 lbs has been shown to significantly increase risk of osteoporosis. Low body mass index (BMI) in men or women dramatically increases osteoporosis and fracture risk, as well as increasing risk of falls. In addition, small-boned women have an increased risk of fracture irrespective of bone density due to the decrease in bone mass.

    Having either a parent or sibling who has had osteoporosis, a spine or hip fracture, or another fragility fracture increases your risk of getting osteoporosis.

    Smoking, drinking alcohol to excess, or leading an inactive lifestyle puts you at risk for osteoporosis. These modifiable risk factors are often major contributors to early osteoporosis in both men and women. In women, tobacco use causes menopause three years earlier than it would occur in a nonsmoking woman. In both men and women, tobacco inhibits normal bone metabolism. Alcohol abuse is a major contributor to osteoporosis (especially in men) because it results in abnormal bone metabolism and is associated with malnutrition. In addition, alcohol abuse carries with it an increased risk of injury and falls, which is dangerous for a person with weakened bones.

    Some ethnic groups are more at risk than others. Although risk is higher among Caucasian and Asian women, African-Americans as well as Hispanic-Americans are also at risk for osteoporosis. Among African-American women, for example, 10% over the age of 50 have osteoporosis, and another 30% have low bone density.

    Table 1.  Risk Factors for Osteoporosis

    Things you can't change Things you can change
    Age (women: over 50; men: over 60) Stop smoking
    Female gender Drink no more than 2 alcoholic drinks per day, and no more than 6 drinks per week
    Being tall, having a small frame, or a slender build (weight under 128 lbs or BMI below average) Get enough exercise, but not so much as to induce amenorrhea (women)
    Family history (mother, father, or sibling) of osteoporosis or hip or spine fracture Get adequate calcium and vitamin D
    Race (Caucasian or Asian ancestry at greater risk than Hispanic. African?American at lower risk than previous groups; however, all groups have elevated risk with increased age or other factors) Avoid certain medications (see Table 2)
    Menopause ?
    Certain diseases (see Table 3)
    History of previous fracture?especially after age 50
    Confusion or dementia and/or unsteady gait and frequent falls that cannot be reversed with treatment.

    Certain drugs increase your risk for osteoporosis by decreasing calcium absorption and vitamin D metabolism, and/or by directly affecting bone formation and breakdown Table 02.

    Table 2.  Drugs that Increase Your Risk for Osteoporosis

    Major culprits
    Corticosteroids at all ages, and also inhaled corticosteroids in the elderly (Prednisone, Medrol, etc.)
    Phenytoin (Dilantin), Phenobarbitol (possibly other, newer anticonvulsants as well)
    Aluminum?containing antiacids (not the more common magnesium containing ones)
    Warfarin (Coumadin), Heparin
    Excessive thyroid hormone replacement (often taken to shrink a thyroid mass)
    Benzodiazipines (Valium, etc)
    Any treatment for prostate cancer.
    Most (possibly all) chemotherapy agents (including interferon, etc.)
    Methotrexate (possibly other, newer rheumatoid arthritis drugs as well)
    Other drugs/medications also associated with decreased bone density
    Insulin
    More than five years of continuous tetracycline use or excess vitamin A or use of oral vitamin A derivatives for acne treatment.
    Gonadatropin?releasing hormone treatment for endometriosis
    Caffeine (also contained in many headache medications)
    Certain diuretic medications (?loop diuretics? such as Lasix, Demidex, Bumex)
    Cholestyramine use for more than five years (used to lower cholesterol)

    Some diseases increase your risk of osteoporosis by affecting bone metabolism Table 03.

    Table 3.  Diseases Associated with Decreased Bone Density

    Overactive parathyroid glands
    Overactive thyroid gland
    Inflammatory bowel disease (Crohn's or other colitis; not irritable bowel)
    Severe chronic lung disease (emphysema, pulmonary fibrosis, etc.)
    Intestinal sprue, surgery to remove part of the stomach or small intestine, or other causes of malabsorption in the upper intestinal tract
    Cystic fibrosis
    Renal tubular acidosis or chronic renal dialysis
    Chronic immunosupression for any type of organ transplantation
    Osteogenesis imperfecta
    Insulin-dependent (type 1) diabetes
    Cushing's disease
    Grand mal seizure disorder
    Rheumatoid arthritis (not osteoarthritis)
    Dementia of any type
    Any disease resulting in muscle weakness or paralysis
    History of any previous fracture, especially after age 50
    Dramatic increase in fracture risk with history fracture of either the spine or hip
    Scoliosis

    There are some factors that have been shown to result in increased bone mass Table 04.

    Table 4.  Factors that Increase Bone Mass

    Morbid obesity (weight over 250 lbs or significantly elevated BMI) without increased risk of falls
    Delayed menopause and/or continuous hormone replacement therapy
    More than three pregnancies combined with adequate calcium and vitamin D intake
    Lifetime high intake of milk products (average three or more servings per day)
    Use of thiazide diuretics for more than five years (decreases calcium excretion)
    Use of statin lipid-lowering medications (Zocor or Pravachol or Mevacor) for more than three years
    Lifetime history of extremely heavy weight-bearing activity (involving regular, continuous lifting of more than 40 lbs)

    Your doctor will perform a complete physical exam, and will review your medical history when diagnosing osteoporosis. Diagnosis can be elusive among people with brittle bone disease, mainly because its symptoms are silent. Your doctor should go over your medical history, including your family history, and give you a full physical exam that includes your height, weight, x-rays, and blood and urine samples.

    Your doctor may run tests to determine bone density and fracture risk. Anyone who has significant risk factors for osteoporosis, especially older women, should undergo bone density tests. These tests measure bone density in different areas of the body; specifically the hips, wrists, and vertebrae, where osteoporosis-related fractures may appear. Such tests can detect osteoporosis before a fracture occurs, and can assess your odds of sustaining a fracture. Also, frequent testing may help to determine your rate of bone loss through the years.

    There are different types of tests to measure bone density.

    Dual energy x-ray absorptiometry of the hip and spine (DEXA) testing measures bone density of the spine, hip, or total body (when necessary, this method may also be used to measure bone density in the wrist). At present, DEXA of the hip and spine is the preferred test for diagnosis and monitoring of osteoporosis because it is the most precise and reproducible. It is also the only test readily available that can accurately measure bone density in the hip, which is one of the most important diagnostic sites. DEXA tests usually take no more than 10 minutes, and give off much less x-ray irradiation than a mammogram. This test is recommended by most experts as the only dependable diagnostic method for women under age 50, or for men of any age.

    CT bone density testing of the spine is used less commonly due to the high x-ray exposure and the inability to measure bone density in any other site than the spine. This test may be used if there are no other options available to you.

    Peripheral dual x-ray absorptiometry (DXA) measures bone density of the wrist, heel, or finger. However, this test may miss osteoporosis that has started in the spine and is not yet evident in the extremities (osteoporosis often begins in the spine in women, sometimes years before it is evident in other sites). Peripheral bone density tests have been shown to miss osteoporosis in up to 30% of cases in women younger than 65 years of age.

    Ultrasound bone density testing is the most recent diagnostic method approved by the U.S. Food and Drug Administration. This method assesses the risk of osteoporosis in one minute, and uses no x-rays. Bone density is determined by measuring the absorption of high-frequency sound waves by the bone in the heel of your foot. By placing your foot into the device, which is shaped like a box, a picture of the heel bone is taken. The sonometer is less costly than other tests, and may serve as a preliminary screening tool for some high-risk populations, or for those who cannot have a DEXA scan. In women over 65 years old this test is fairly specific for osteoporosis, but still may miss up to 20% of cases that would be found on DEXA. In men or younger women, however, there can be a very high false negative rate.

    To prevent osteoporosis, it is critical to take steps to maximize bone growth in childhood and young adulthood. After your bones reach their peak density, it is equally important to take further preventive measures to avoid the gradual loss of bone that can result in low bone density and osteoporosis later in life.

    Maintain healthy eating habits and levels of activity throughout life. Because peak bone mass continues to develop from childhood on through adolescence, parents should pay close attention to the eating and lifestyle habits of their children. Parents should continue to set examples and encourage good eating and lifestyle habits as their children grow to become teenagers and young adults. It is most important to eat a balanced diet with plenty of calcium and vitamin D each day. You should not smoke, and you should limit your intake of soda and caffeine. Other key lifestyle routines that help build stronger bones include doing weight—bearing activities such as lifting weights and walking. Young women in competitive sports (especially swimming or track) should be monitored closely for normal menstrual cycles, and a physician should evaluate any significant changes. Young women should also be monitored closely for signs of eating disorders, as these have become more and more frequent and can result in significant bone loss.

    A bone density test helps to determine your chances of a future fracture. The National Osteoporosis Foundation recommends that all women over age 65 undergo screening. They also recommend that women less than age 65 who have gone through menopause and have at least one risk factor should also undergo screening.

  • Prevention and Screening

    To prevent osteoporosis, it is critical to take steps to maximize bone growth in childhood and young adulthood. After your bones reach their peak density, it is equally important to take further preventive measures to avoid the gradual loss of bone that can result in low bone density and osteoporosis later in life.

    Maintain healthy eating habits and levels of activity throughout life. Because peak bone mass continues to develop from childhood on through adolescence, parents should pay close attention to the eating and lifestyle habits of their children. Parents should continue to set examples and encourage good eating and lifestyle habits as their children grow to become teenagers and young adults. It is most important to eat a balanced diet with plenty of calcium and vitamin D each day. You should not smoke, and you should limit your intake of soda and caffeine. Other key lifestyle routines that help build stronger bones include doing weight—bearing activities such as lifting weights and walking. Young women in competitive sports (especially swimming or track) should be monitored closely for normal menstrual cycles, and a physician should evaluate any significant changes. Young women should also be monitored closely for signs of eating disorders, as these have become more and more frequent and can result in significant bone loss.

    A bone density test helps to determine your chances of a future fracture. The National Osteoporosis Foundation recommends that all women over age 65 undergo screening. They also recommend that women less than age 65 who have gone through menopause and have at least one risk factor should also undergo screening.

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