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Pulmonary Embolism: Jeffrey Ginsberg, MD, FRCPC, discusses the clinical examination for pulmonary embolism.
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Pulmonary Embolism: Jeffrey Ginsberg, MD, FRCPC, discusses the clinical examination for pulmonary embolism.
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Language: EN.
Segment:0 .
>> I'm Joan Stephenson, editor of JAMA's Medical News and Perspectives section. Today, I have the pleasure of speaking with Dr. Jeffrey Ginsberg about pulmonary embolism. Dr. Ginsberg, why don't you introduce yourself to our listeners? >> Hello, my name is Jeff Ginsberg. I'm a Professor of Medicine at McMaster University in Hamilton, Canada. >> Dr. Ginsberg, what do we know about the prevalence of pulmonary embolism in relation to the risk factors? >> The prevalence of pulmonary embolism in the general population is about zero to 1 per 1,000 per year.
About a third of patients will have PE that's provoked by a clinical risk factor, and these risk factors for PE include Hip surgery, knee surgery and neurosurgery, with an odds ratio of approximately 21, major trauma with an odds ratio of about 13; immobility, that is bed rest, complete bed rest, with an odds ratio of approximately 8, active cancer with an odds ratio of approximately 5, leg paralysis due to neurologic disease with an odds ratio of approximately 3, and hormone therapy, including the OCT with a birth control [inaudible] with an odds ratio of approximately 3.
About a third of patients will have a known thrombophilia. For example, Antithrombin deficiency, Protein C or S deficiency, Factor V Leiden, Prothrombin G mutation, or antiphospholipid antibodies. And approximately a third will have unprovoked pulmonary embolism. Presumably, some have yet-to-be-discovered thrombophilias. >> You place an emphasis on the Wells Criteria because this combination of findings has good reliability, it's easy to use in clinical practice, and it requires no laboratory or radiographs.
Can you describe the criteria for our listeners and convince them of its reliability as a score? >> The Wells scoring system is a system whereby points are assigned for certain characteristics, either clinical signs or symptoms, risk factors, or the way the patient presents. For example, clinical signs or symptoms of concomitant deep vein thrombosis with leg swelling and pain or palpation on the deep veins of the legs imparts a score of 3 points.
In addition, no alternative diagnosis that's likely or more likely than pulmonary embolism imparts a score of 3 points. Heart rate of greater than 100 beats per minute imparts a score of 1.5 points. Mobilization or surgery in the last four weeks imparts a score of 1.5. Previous history of deep vein thrombosis or pulmonary embolism imparts a score of 1.5. The presence of hemoptysis imparts a score of 1.0. And cancer actively treated within the last six months imparts a score of 1.0. The score is taken or is calculated by adding up the sum of each of the characteristics to come up with a summary score.
These can be categorized as low pretest probability with a score of less than 2, moderate with a score of 2 to 6, and high with a score of greater than 6. Now, the validity of this model has been tested in a number of scenarios in different studies in different centers and has been validated in each of the settings in which it's been looked at. It also has a very good intra-observer variability with Kappa scores in the range of 0.8 indicating excellent intra-observer agreement.
>> The D-dimer has an important role when interpreted together with the Wells criteria. Why is it important to apply the Wells criteria and estimate the probability of pulmonary emboli before reviewing the D-dimer result? >> Well, simply put, in the studies in which it's been evaluated, the Wells score has been used when calculated prior to the results of the D-dimer being available. The Wells score has some subjectivity. And so knowledge of the D-dimer results has the potential to influence the assessment of pretest probability and influence and perhaps bias results of the Wells score.
Therefore, the results of the study are only generalizable under these conditions, in which the D-dimer result is not known until after the Wells score is calculated. >> Are the sensitivity and specificity of the D-dimer constant across patients with different risk factors? >> No. The specificity tends to be lower in the [inaudible] patients, in patients with major trauma, patients who've undergone surgery, and cancer patients. Each of these is a risk factor for the development of pulmonary embolism.
And in fact, it tends to produce falsely positive results in and of themselves. >> Tell us in what setting the Wells criteria and D-dimer actually rule out pulmonary emboli. >> This depends very much upon the sensitivity of the D-dimer assay that's being used. In general, we think of D-dimers as being either highly sensitive or moderately sensitive. Highly sensitive would be 95% or more, and moderately sensitive would be less than 95%.
And so with a moderately sensitive or highly sensitive assay, in the presence of a low pretest probability, a normal D-dimer assay excludes pulmonary embolism with high reliability. In the presence of a moderate or a high pretest probability according to the Wells criteria, only a highly sensitive D-dimer assay reliably excludes the diagnosis of pulmonary embolism. >> What are the pragmatic reference standard tests for clinicians to diagnose pulmonary emboli?
>> Historically, adequately performed contrast pulmonary angiogram with big films has been considered the reference standard. However, it's rarely performed now. And so a lot of radiologists have lost the expertise in performing the task. And so now we tend to use constant reference standards, which are quite common. And they include combination of CTPA or computerized tomographic pulmonary angiography, [inaudible] ultrasonography, pretest probability, and D-dimer results.
For example, pulmonary embolism can be reliably diagnosed if an intraluminal filling defect is seen on a conventional pulmonary angiogram with big films. Or if there's a segmental or greater intraluminal filling defect on CTPA or in the presence of a high-probability lung scan with a moderate or high pretest probability, or in any situation where there's an abnormal and diagnostic compression ultrasound for deep vein thrombosis because presence of deep vein thrombosis in a patient with suspected pulmonary embolism is sufficient to make a diagnosis of pulmonary embolism.
On the other hand, excluding pulmonary embolism can be performed by normal pulmonary angiogram, a normal perfusion lung scan, a normal CTPA, and/or a moderate or non-diagnostic CTPA or ventilation perfusion lung scan with normal serial and [inaudible] ultrasonography or a normal D-dimer assay combined with a low pretest probability of pulmonary embolism.
>> Is there anything else JAMAevidence users should know about diagnosing pulmonary embolism? >> Yes, I think the history of the diagnosis of pulmonary embolism is interesting in the sense that in the '70s and '80s, 1970's and 1980's, we relied quite heavily upon [inaudible] to make a diagnosis or refute diagnosis of pulmonary embolism. And then in the late 1980's and early 1990's, we threw away the clinical diagnosis because individual signs and symptoms were considered unreliable for the diagnosis of pulmonary embolism.
So it was considered analogous to flipping a coin. We've now come to realize and come 360 degrees and realize now that the pretest probability assessment, when used either with conditions gestalt or via a validated clinical prediction rule, such as the Wells prediction rule, has quite a bit of clinical utility as an adjunct to the diagnosis of pulmonary embolism. It can be used in combination with other diagnostic tests to make or refute the diagnosis of pulmonary embolism when it's suspected.
I think, finally, I would make comment that the range of symptoms and signs of pulmonary embolism are nonspecific and also insensitive. And so a patient can have no symptoms and have pulmonary embolism. So the key to reducing mortality from pulmonary embolism is to have a high index of suspicion when a patient presents with symptoms that are compatible with pulmonary embolism. >> Thank you, Dr. Ginsberg, for this overview of pulmonary embolism.
For additional information about this topic, JAMAevidence subscribers can consult the online chapter on pulmonary embolism in the Rational Clinical Examination. This has been Joan Stephenson of JAMA talking with Dr. Jeffrey Ginsberg for JAMAevidence.