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In October 2004, Surgeon General Richard H. Carmona issued an alarming report: within 15 years, half of the United States population over the age of 50 would be at risk for fractures from osteoporosis and low bone mass. Most of those at risk will not be aware they have the condition, even though 1.5 million Americans a year suffer an osteoporosis-related bone fracture and as many as 34 million suffer osteopenia of the hip—a lower-than-normal bone mass density considered a precursor for osteoporosis.
Osteoporosis-related bone fractures are a particularly acute problem among Caucasian women: those over 50 have a 40% chance of suffering a fracture over the course of their lifetime, compared to 13% for Caucasian men. Although the rate is lower for other ethnic groups and males, it is believed to be rising in some subgroups, particularly Hispanic women.
A hip fracture in an older person can be a devastating blow. The risk of mortality within the first 3 months of the event is up to four times greater than average, and 20% of elderly hip fracture victims either die or wind up in a nursing home within a year after the event. Given such morbidity, it is little surprise that the annual cost of treating osteoporosis in the United States is $18 billion a year and rising.
Radiological diagnostic tools for osteoporosis have been used since the 1950s, when radiographic absorptiometry (RA) testing of metacarpals and phalanges was first used to identify potential victims of osteoporosis and their fracture risk. In recent years, ultrasounds of the tibia and heel have become an inexpensive method of screening patients at risk for osteoporosis that can be performed in a physician’s office. However, questions have been raised about the complexity of the calculations required to determine bone mass density (BMD), as well as the accuracy compared to other technologies currently available. Ultrasound scans are currently popular in developing countries, such as those in Eastern Europe, according to Leon Lenchik, MD, section head of musculoskeletal radiology at Wake Forest University Baptist Medical Center in Winston-Salem, NC.
Quantitative computed tomography (QCT) is used to calculate the differential absorption of ionizing radiation by calcified tissue. It can be performed with a standard CT scanner, with attenuation measurements compared with standard references regarding bone masses in same-sex peers. However, QCT exposes patients to a relatively high dose of radiation, and its cost is prohibitive compared to other technologies.
THE GOLD STANDARD
In the United States, the radiological gold standard for diagnosing osteoporosis has been dual x-ray absorptiometry (DXA), confirms Harry Genant, MD, professor emeritus at the University of California San Francisco and founder of UCSF’s Osteoporosis and Arthritis Research Group.
DXA uses two x-ray beams—one low-energy and one high-energy—to diagnose BMD. Low-energy beams experience greater attenuation than high-energy beams, and bone attenuates x-rays more than soft tissue. Based on the discrepancies between the two beams, corrections for soft tissue can be made. It has proven the most effective diagnostic tool since it was introduced in the United States in the late 1980s, says Genant and Lenchik.
DXA scans of BMD are expressed as t-scores and z-scores. The t-score is the comparison of the patient’s bone mass with that of a young adult of the same gender with peak bone mass. The z-score reflects the amount of bone mass density of the patient compared to peers in their age group, and can also indicate whether the osteoporosis is a secondary symptom of another disease.
According to the World Health Organization, any t-score of -1 or above is considered normal. Any score below -1 but above -2.5 is considered a sign of osteopenia. A score below 2.5 is diagnosed as osteoporosis. The risk for bone fracture doubles with each drop of one tenth of a point on a t-score below the mean. It also doubles for each decade a patient is over the age of 50. Osteoporosis is typically caused by aging and menopause, but can also be related to a number of diseases, including cystic fibrosis, hyperparathyroidism, and porphyria.
Genant says there were three phases in the widespread use of DXA: the first was from its introduction in 1987 to the mid 1990s, when DXA was confined mostly to researchers conducting clinical trials. The second wave occurred in the mid 1990s, with the introduction of a class of antiresorptive therapeutic drugs known as bisphosphonates (ibandronate and risedronate are the leading medicines in this category). “That created an increased demand for the wider use of densitometry,” Genant says, moving DXA devices into the radiology departments of most hospitals. The last wave occurred at the beginning of the decade, when Medicare assigned a billing code for the use of DXA to test women over 65 for the onset of osteoporosis. “That drove the market even further, with [such equipment] being used by primary care physicians, endocrinologists, and rheumatologists,” Genant notes.
“Both ultrasound and QCT have been around for many years, so it’s not new technology as such, it is just a question of how clinically relevant the results are,” Lenchik says. “Most people believe data from the other machines are difficult to interpret.” Lenchik believes future protocols may be developed to integrate the use of ultrasound with DXA, but adds that no clear vision to integrate the two methods has emerged.
“With ultrasound, we thought it would be a good technology because it is cheaper and portable, but no one has taken the time to sort out the relevant issues,” Lenchik says. In the meantime, the use of DXA has become widespread.
“If I had to be optimistic regarding one clinical application of ultrasound, I would say it would be good in pediatrics, when there may be kids of an age where the dose of radiation is an issue, but that’s at least 5 or 10 years away,” Lenchik adds. There is also a substantial reimbursement issue regarding ultrasound; Medicare reimburses about $40 per procedure, less than a third of what it pays to employ DXA.
A NEW TWIST: VERTEBRAL FRACTURE
DXA does have its shortcomings: it has not proven to be particularly effective in diagnosing vertebral fractures, which occur in about one third of women over the age of 65. Only 30% of such fractures are diagnosed as the result of any radiology-based examination. The osteoporosis community is being urged to pay closer attention in terms of spotting such fractures, note both Genant and Lenchik. The most telling precursor remains self-reported height losses in patients of two inches or more.
Lateral x-rays remain the most effective method of diagnosing vertebral fractures. “The workhorse for identifying fractures is still plain film,” Lenchik says. A lateral form of DXA has been introduced in recent years to make such diagnoses, but, according to Genant, Medicare’s reimbursement for lateral DXA is a fraction of what is received for a central BMD DXA (about $40 versus $140). Although both a central and lateral DXA can be performed in a single session on some densitomers, it remains unclear whether the extra reimbursement is prompting radiologists to use both methods. Lenchik notes that there is less parallax present in a lateral x-ray, and as a result, about 15% of lateral DXA examinations are indeterminate for diagnosing vertebral fractures. But patient convenience in performing both procedures in one appointment is a consideration.
PATIENT COMMUNICATION
Improvements in DXA aside, it is often difficult to communicate to patients their t-scores and z-scores in a way that effectively lets them know of their elevated risk for bone fracture. Patients are usually notified that they have an elevated risk of bone fracture, but often without any hard statistics attached to that probability. Both Genant and Lenchik believe that BMD results will eventually be translated into what is called the absolute fracture risk method. Absolute fracture is considered a more holistic measurement method. It takes into account not only the DXA data but other relevant information, including the patient’s personal history of fracture as an adult; whether they smoke or drink; their physical activity; and whether they experienced estrogen deficiency at an early age.
“We will move in that direction,” Genant says. “The researchers in the field are generally supportive of using that method as opposed to t-scores.”
Lenchik believes it will eventually be customary for DXA devices to calculate an absolute fracture risk for each patient and include it in the printout for the physicians, expressed as a percentage of risk over a specific timeline: 1, 5, or 10 years.
“It makes a lot more sense to identify people with a high risk for fractures, and give them osteoporosis medication, eliminating the step of the t-score, which is hard [for primary care physicians and other providers] to grasp,” Lenchik says.
Codes Utilized for BMD Assessment
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According to a study cited by one vendor on employing absolute fracture risk, 70% of patients who received such an assessment following a free ultrasound BMD test followed up with their physicians, and 40% received osteoporosis medication. Among those patients who received just t-scores, only 60% followed up with their physician and just 20% received medication.
Still, many issues remain regarding the protocols to be used in determining absolute fracture risk, such as whether it would be pegged to hip bones, vertebrae, or a variety of locations, or just give a patient an overall risk assessment.
Also, absolute risk data would have to be carefully communicated to patients, because to a layperson, they may not sound statistically relevant.
“If you tell a patient they have a 1% risk of sustaining a fracture over the next year, they may not see it as a high enough risk to seek intervention,” Lenchik says. “They may see it as a 99% chance that nothing is going to happen to them at all.”
According to Lenchik and Genant, the World Health Organization is currently formulating protocols for the absolute risk fracture method and is leaning toward a risk assessment over 10 years, with a risk given for all sustaining any type of osteoporotic-related bone fracture.
TREATMENT RESPONSE
Radiological techniques such as DXA have also been used to monitor treatment of patients with osteoporosis, to determine whether BMD loss has been slowed or arrested. But with current research, they will eventually have a rapidly growing second duty: monitoring the accumulation of new BMD.
According to Genant, new treatments are being developed to add BMD, many of which involve clinical studies being conducted by a company he founded. One approved for current use, selective estrogen receptor modulators (SERMs), simulates the beneficial qualities of estrogen in maintaining and adding to BMD, without inflaming the uterus or other reproductive organs.
Another treatment involves specifically timed doses of synthetic parathyroid hormone, which can also arrest BMD loss and even cause regeneration.
A third drug, strontium ranelate, is a heavy metal that is approved for use in Europe. Like SERMs and parathyroid hormones, strontium ranelate also helps to restore BMD.
Greater Vigilance Called for in Diagnosing Vertebral FractureAccording to the National Osteoporosis Foundation, some 30 million women nationwide suffer osteoporosis or osteopenia, a precursor to the disease. Vertebral fractures pose one of the greatest threats for patient mobility and overall quality of life. Loss of function is comparable to that of hip fractures, with sufferers often having difficulty with daily activities such as rising from a chair, bathing, dressing, cooking, and walking. The risk for osteoporosis-related vertebral fractures among women begins to increase at the age of 45, with an incidence of 0.2 per 1,000 person-years, eventually increasing to 1.2 per 1,000 person-years after the age of 85. Studies of vertebral fractures in men and women in Europe indicate a rate of 10% to 24%, with rates as high as 50% among women between the age of 50 and 85. In the United States, the average is about 25%. Although the per-incident mortality and morbidity rates for vertebral fractures are not as high as for hip fractures, they quickly begin to climb as vertebral fractures multiply, rising from 23 per 1,000 person-years for a single vertebral fracture to nearly 45 among patients with five or more fractures. Yet vertebral fractures are among the most difficult of bone fractures to diagnose. According to the American Medical Association, only about 30% are accurately diagnosed using radiographic or other radiological techniques, with lateral chest x-rays remaining the most reliable method for an accurate diagnosis. Among the challenges posed in diagnosing vertebral fractures is the actual difficulty in visualizing them. In many instances, radiologists will conclude instead that phantom or pseudofractures exist. For example, a lateral projection that is really an oblique projection may lead to the appearance of fractured vertebrae. Similarly, lateral projections of patients with scoliosis may yield a similar diagnosis. And some abnormalities in vertebral shape can also mimic a fracture. Writing in the October 2004 issue of the American Journal of Roentgenology, Leon Lenchik, MD, Lee F. Rogers, MD, Pierre D. Delmas, MD, and Harry K. Genant, MD, issued a call for action to more accurately diagnose vertebral fractures. Among their recommendations: diagnosing vertebral fractures when there is a loss of height of the anterior, middle, or posterior dimension of the vertebral body that exceeds 20%. If there is ambiguity in the diagnosis, additional images or study views should be ordered. They also recommend that radiologists stick to a more uniform terminology, particularly when discussing potential fractures with patients. “A radiologic hedge can adversely affect patient care by preventing a patient who would otherwise benefit from pharmacologic therapy from receiving it,” they write (see Figure 1).
In addition to the Lenchik et al call to action, the International Osteoporosis Foundation and the European Society of Musculoskeletal Radiology have launched a “vertebral fracture initiative” in order to increase accurate diagnoses of the condition. Among its recommendations: combine bone mass densitometry examinations with vertebral fracture examinations, and report all borderline diagnoses as “fractured.” The initiative’s goal is to increase accurate reporting of vertebral fractures by as much as 30%. |
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—R. Shinkman |
Figure 1. Drawings illustrate the semiquantitative method of diagnosis and grading of vertebral fractures developed by Harry Genant, MD. Vertebral fracture is diagnosed when reduction of height in anterior, middle, or posterior dimension of vertebral body exceeds 20%. Approximate degree of height reduction determines assignment of grade to vertebra. Fractures are classified as wedge, biconcave, or crush, depending on whether anterior, middle, or posterior portion of vertebral body is most diminished in height. Reprinted with permission: Lenchik L, Rogers LF, Delmas PD, Genant HK. Diagnosis of osteoporotic vertebral fractures: importance of recognition and description by radiologists. AJR Am J Roentgenol. 2004 Oct;183(4):949-58. Ron Shinkman is a contributing writer for Decisions in Axis Imaging News.
