THE DISEASE COMPUTING OSTEOPOROSIS RISK MEASURING BONE MASS WHO SHOULD BE TESTED? FRACTURE PREVENTION OPTIONS FOR OSTEOPOROSIS PREVENTION

In the fast-moving field of women's health, few areas have evolved more rapidly than the detection, prevention, and treatment of osteoporosis. A generation ago, osteoporosis was characterized as "a silent disease." The term made sense at the time; osteoporosis wasn't commonly recognized until a broken vertebra or hip signaled its presence. Today, it no longer has to go unnoticed. The widespread availability of technology to measure bone density has made it possible to identify women who are at risk for osteoporosis long before fractures are imminent.

THE DISEASE

"Osteoporosis," literally translated, is "a condition of porous bones." The term provides a pretty good description of the swiss-cheese appearance of osteoporotic bone seen under a microscope.

Bone is composed of a meshwork of collagen fibers that is inlaid with calcium and phosphate. The minerals are mixed with water to form a hard, cement-like substance called hydroxyapatite. Sodium, magnesium, and potassium are also present in smaller amounts.

Calcium's importance extends far beyond the bone. It circulates throughout the body to regulate heart rate, muscle contractions, blood pressure, and other systemic functions. When blood levels of calcium drop below the level necessary to execute these functions, it is replenished from bone.

Resorption, the release of calcium from the bone into the blood, is coupled with another process, formation, in which bone is rebuilt. The continuous resorption /formation cycle is known as bone remodeling. When formation outpaces resorption, bone density increases; when resorption takes place faster than formation, bone loss occurs. If bone loss continues over time, osteoporosis may develop.

COMPUTING OSTEOPOROSIS RISK

Today, osteoporosis is defined in terms of bone density, a measurement of bone in grams per square centimeter. The number is meaningless out of context. However, like the figure that represents serum cholesterol level, it can be used to place us somewhere on a population spectrum. Researchers have evaluated the bone densities of thousands of women, and have determined who have had osteoporotic fractures and who have not. Because women who were in their 30s, when bone mass is generally at its peak, are at the lowest risk for fractures, their average bone mass is used as a reference point.

Osteoporosis is now defined in terms of standard deviations from the average peak bone mass, also called a T-score. Standard deviation is a statistical term used to express the average amount by which an individual varies from the norm. For example, if the average weight of nine women is 125 pounds and one standard deviation is 12.5 pounds, then those who weigh between 112.5 pounds and 137.5 pounds are one standard deviation from the mean, and those who weigh between 100 and 150 pounds are within two standard deviations from the mean. A 100-pound woman is said to be -2 standard deviations and a 150-pound women is said to be +2 standard deviations from the mean. The first woman's T-score would be -2, the second woman's, +2.

The World Health Organization (WHO) has suggested a classification system based on these values. By that system, people with a T-score of greater than -1 are considered to be at low risk for fractures. Those with T-scores of -1 to -2.5 are considered to have osteopenia (low bone mass) and are at greater risk for fractures. Those who have T-scores of -2.5 or lower are defined as having osteoporosis, even though they may not have broken a bone.

However, a T-score isn't the only measure of fracture risk. Other factors such as low muscle mass, balance problems, poor eyesight, and use of antianxiety medications can increase the risk of falls and therefore fractures. Because such problems tend to increase with age, a 70-year- old woman with a T-score of -2 is at greater immediate risk of breaking a hip than is a 50-year-old with the same T-score, even though their lifetime risk may be the same.

MEASURING BONE MASS

In recent years, dual-energy x-ray absorptiometry (DXA), which delivers only a fraction of the radiation dose of a chest x-ray, has become the gold standard for assessing bone density. Although DXA can measure bone density at any point in the body, it is usually used to take measurements at the hip and spine -- the areas where serious osteoporotic fractures are most likely to occur. The procedure takes 10-15 minutes, during which the patient lies on a table while the imager passes over her body. A computer calculates the density of the patient's bones and delivers the results in grams per square centimeter and as a T-score.

A modification of this technique, peripheral DXA or pDXA, measures bone density in the arm. This procedure is performed in about 5 minutes with a scanner the size of a desktop computer, which enables pDXA to be used in clinicians' offices, workplaces, and shopping centers.

Another portable technology, the clinical bone sonometer, became available in 1998. The Sahara, the first bone sonometer to be approved by the Food and Drug Administration, is a compact, 22-pound device that employs ultrasound (high-frequency sound waves) to measure bone density at the heel and a computer to record the speed of the waves and the degree to which they are diminished as they pass through the heel. The procedure takes less than a minute to complete. The device issues a printout providing an estimate of bone density in grams per square centimeter and as a T-score.

Medicare, and presumably other insurers, cover any of the above methods because all are FDA-approved for bone measurement. However, the three aren't interchangeable. DXA is the preferred procedure because it measures bone density at the spine and hip, where bone loss occurs more rapidly. It is possible for a newly postmenopausal woman to have a DXA measurement indicating bone loss at the spine and hip even though her score on pDXA or bone sonometry is normal. There is evidence that heel and arm measurements are more reliable indicators of overall bone density in women over 65 than in younger women. However, they are still not as precise as DXA.

Because DXA isn't universally available, pDXA or sonometry may be the only options for initial screening. Women in their 50s who have a normal T-score on a heel or arm are probably not at high risk for fracture in the immediate future. For women over 60, a good result on pDXA or sonometry is even better news. By the same token, a T-score of -1 or lower on either pDXA or sonometry is reason for referral to DXA testing. Because bone loss can occur rapidly in postmenopausal women, it is probably wise to be retested within 2 years.

WHO SHOULD BE TESTED?

Experts are still debating who should receive bone-density screening, but groups are getting closer to a consensus. Bone density screening for all women over age 65 is covered by Medicare, and the National Osteoporosis Foundation has suggested guidelines for testing younger postmenopausal women.

The Medicare Bone Mass Measurement Coverage Standardization Act, which went into effect in 1998, covers bone mass measurement for estrogen-deficient women (in essence, all postmenopausal women); people with vertebral abnormalities; patients undergoing long-term steroid therapy, which often leads to osteoporosis; and people with primary hyperparathyroidism -- a condition that results in the excessive release of calcium from the bone. It also covers bone-mass measurement to monitor response to drug therapy for osteoporosis. Medicare will pay for repeat measurements every 2 years.

The National Osteoporosis Foundation's guide for physicians also suggests a bone density test for every woman 65 and older. In addition, the foundation recommends bone measurement for postmenopausal women under age 65 who have sustained a bone fracture in adulthood, who have a family history of osteoporosis, who are thin, and who smoke.

Such guidelines are developed from research conducted primarily in Caucasian women, but a study of 48,000 postmenopausal women, the National Osteoporosis Risk Assessment, has been mounted to collect data on women in other ethnic groups. Early reports indicate that osteoporosis may be more prevalent in Hispanic, Native American, and Asian women, and that almost one third of African American women, a group once believed to be exempt, may be affected.

FRACTURE PREVENTION

Three options -- estrogen, alendronate (Fosamax) and raloxifene (Evista) are FDA-approved for osteoporosis prevention. The three plus calcitonin (Miacalcin) are available for treatment. All should be accompanied by 1,200 mg calcium and 400 IU vitamin D each day. Weight bearing exercise is also recommended. The doses and effects of the preventive approaches are summarized below.

OPTIONS FOR OSTEOPOROSIS PREVENTION

The following chart reads as follows:

Row 1: ESTROGEN

Row 2: FOSAMAX

Row 3: EVISTA

Dose                       0.3-0.625 mg/day, prevention and
                             treatment

                             5 mg/day, rpevention 10 mg/day,
                             treatment

                                      60 mg/day, prevention

Effectiveness after 2 years    0.3 mg Estratab increased bone
in women taking adequate     density in lower spine by 1.76%, in
calcium and vitamin D           hip by 1.48%; 0.625 mg Premarin
                                        increased bone density in lower
                                        spine by 3.5%, in hip by 2.5%.

                             5 mg/day increased bone density in
                             lower spine by 2.7%, in hip by 1.3%

                             Increased bone density in lower
                             spine by 1.6%, in hip by 1.6%

Fracture prevention          0.625-mg dose decreased hip
                             fractures by 50-60% over 6 years

                             5 mg/day for 2 years, then 10
                             mg/day for 1 year reduced hip
                             fractures by 51%, spinal fractures
                             by 47%

                             Reduced spinal fractures by 52%
                             over 2 years

Side effects                 Breast tenderness, swelling. May
                             increase risk of uterine cancer (if
                             not taken with a progestogen),
                             breast cancer, gallblader disease,
                             deep-vein blood clots, and
                             pulmonary embolism.

                             Inflammation of esophagus,
                             heartburn, abdominal pain,
                             diarrhea, nausea. Esophageal ulcers
                             in patients who do not follow
                             instructions to take with 8 ounces
                             of water on an empty stomach and
                             remain upright for at least 30
                             minutes thereafter

                             Hot flashes, leg cramps, increased
                             risk of deep-vein blood clots and
                             pulmonary embolism