Q&A: Underdiagnosis in Osteoporosis

August 10, 2015

This Q&A series explores radiology’s role in overdiagnosis in a variety of conditions. Here, we discuss osteoporosis.

Overdiagnosis is commonly discussed in areas like breast imaging, where screening is widely conducted and media interest is high. While it’s under the radar for other diseases, it’s a big enough topic in the medical world to warrant a dedicated issue in Academic Radiology. Its August 2015 issue is devoted to overdiagnosis, a term used for disease that’s correctly diagnosed, but at the earliest stages when treatment may not be necessary and might even be harmful to the patient. This is in contrast to false positives, when the diagnostic test incorrectly indicates the possible presence of disease.

Overdiagnosis is more prevalent in modern times because the definition of disease has expanded, said Saurabh Jha, MBBS, assistant professor of radiology at the Hospital of the University of Pennsylvania, and guest editor of the Academic Radiology issue. “The rationale is the very intuitive concept that if we catch disease early on, we’ll avoid morbidity and mortality, that prevention is better than cure.”

With more advanced technology, radiologists can see deeper into structures in the body, discovering new (but often innocuous) abnormalities. Another reason for a growth in overdiagnosis is cultural. The division between “diseased” and “healthy” is arbitrarily set.

“There’s always going to be disputes about where the boundary takes place,” said Jha, with nothing magically happening at that threshold where disease is defined. However, in the United States, that threshold is often set at a place where doctors won’t miss any disease, erring on the side of overdiagnosing a person who doesn’t need treatment. “We live in an extremely risk averse environment.”

This Q&A series looks at a number of diseases that may be overdiagnosed in the United States, where we might be “treating health as opposed to solving sickness,” according to Jha.

Here’s our Q&A on overdiagnosis in osteoporosis with Alexander T. Ruutiainen, MD, assistant professor of clinical radiology at the Hospital of the University of Pennsylvania.[[{"type":"media","view_mode":"media_crop","fid":"40174","attributes":{"alt":"","class":"media-image media-image-right","id":"media_crop_2088701871812","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"4089","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"float: right;","title":"Alexander T. Ruutiainen, MD","typeof":"foaf:Image"}}]]

Are reports of overdiagnosis of osteoporosis accurate or exaggerated?

They are quite exaggerated! Osteoporosis is a really serious disease; patients who suffer fragility fractures have an increased risk of death, disability, and loss of functional independence. Unfortunately, this public health threat remains underappreciated. Rather than overdiagnosing patients, our health care system is actually underdiagnosing them. For example, screening studies have shown that about one-third of ambulatory women over age 65 have undiagnosed osteopenia, and about 7% of them have frank osteoporosis! It would be dangerous to suggest that we should be doing less, rather than more.

Are DXA scans a waste or cost effective?

DXA is cheap, widely-available, and uses only a minimal amount of radiation. By contrast, the cost of treating a hip fracture can be over $11,000 in the first year alone, not to mention the emotional costs associated with hospitalization and the potential loss of independent living. Since the early detection and treatment of osteoporosis can prevent some of these fractures, screening for bone fragility using DXA is a really good deal-for both the health care payers and individual patients. 

Is osteoporosis defined too liberally or not liberally enough?

The definition of osteoporosis is based on a statistical cutoff that was set by the World Health Organization; it is simply a definition, and therefore neither liberal nor stringent. What really matters is a patient’s actual risk of fracture. To calculate that, you need to know the Bone Mineral Density (which is provided by DXA), and a few bits of clinical information (age, weight, smoking history, etc.). The University of Sheffield provides a great online calculator called FRAX to estimate the 10-year probability of a fracture.

Should the term osteoporosis only be used for postmenopausal women or men over age 50?

This is a great question, and a common source of confusion. DXA can only diagnose osteoporosis in just these groups of people. That is, it is inappropriate to talk about “osteoporosis” or “osteopenia” in younger populations-particularly children. Although we can still use DXA to help younger patients, we have to analyze the “Z-scores” (rather than the “T-scores”) that compare patient to age- and ethnicity-matched controls. For them, we report the bone mineral density as being “above” or “below” the expected range for age.

Does overdiagnosis (or underdiagnosis) vary based on ethnicity?

The diagnosis of osteoporosis is based on a statistical cutoff where patients are compared to young Caucasians from the NHANES III database. This means that it is defined in exactly the same way for everyone-which is good, because consistent definitions are important in medicine. On the other hand, we know that the actual fracture risk varies between ethnicities. That’s why calculating an individual patient’s absolute risk score using a tool like FRAX is so important; it incorporates the patient’s demographics into the risk assessment.

Does the World Health Organization’s definition of osteoporosis as a T level of -2.5 overdiagnose too many patients?

Not at all. These patients are at a high risk for fracture, and most of them would benefit from treatment to increase the strength of their bones (though individual treatment decisions should always be discussed with their doctor).

Should the T score cutoff of -2.5 be adjusted based on the measurement site?

In the past, there has been a misconception that a patient might have “osteoporosis in the hip,” but only “osteopenia in the spine.” That is incorrect. We know that osteoporosis is a systemic disease that affects all of the weight-bearing bones of our bodies. That’s why we assume the worst case scenario and report the lowest of the T-scores from the spine, the total hip, the femoral neck, and occasionally the one-third radius. To make that approach work, we have to use the same cutoff for each of these sites.

What advice do you have for radiologists reading DXA scans?

To generate a clinically useful DXA report, radiologists have to do much more than just copy numbers from a scanner. We need to actually interpret and critically analyze the provided images. This means being familiar with up-to-date recommendations on DXA reporting, which are available from the International Society for Clinical Densitometry. It also means conducting Quality Assurance on our scanners, technologists, and DXA images-such as with precision assessments. As a specialty, we need to start viewing densitometry not as an afterthought, but as a modality that is equally important to our radiographs, CTs, and MRIs.