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Deep Vein Thrombosis: Philip S. Wells, MD, MSc, discusses the clinical examination for deep vein thrombosis.
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Deep Vein Thrombosis: Philip S. Wells, MD, MSc, discusses the clinical examination for deep vein thrombosis.
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>> I'm Joan Stephenson, Editor of JAMA's Medical News and Perspectives section. Today I have the pleasure of speaking with Dr. Philip Wells about deep vein thrombosis. Dr. Wells, why don't you introduce yourself to our listeners. >> Okay. Hello there. My name's Dr. Phil Wells. I'm Professor, Chair and Chief of the Department of Medicine at the University of Ottawa. >> And, Dr. Wells, what do we know about the prevalence of deep vein thrombosis, and are there important demographic characteristics? >> So I guess more commonly we talk about incidents rather than prevalence, so the incidents is about one in a thousand per year, which interestingly, is about one in 150 per year in patients who are over 70 years of age.
With respect to prevalence, that depends on the population that's being studied, but in general, in an ultrasound department, about 15% of patients who are referred for a query of deep vein thrombosis will have that diagnosis made. The important demographic characteristics I would say are that it is more common in older people, it's more common in males, cancer patients and patients who are post-major surgery or after major trauma. >> Which symptoms increase the probability of deep vein thrombosis?
>> Well, it's a constellation of symptoms and signs and history that are really most important, but I think some of the symptoms that are particularly important to be aware of are to start with the fact that it's generally unilateral in the symptoms, and the specific ones that are of importance are probably mostly edema, a duskiness to the extremity, swelling, of course, which goes along with the edema, a description of pain which fits in a distribution of the deep vein pathway within the leg, and sometimes you actually will see, and the patients will complain of the formation of new veins, which we call collateral veins on the surface of their skin.
>> Which history and physical examination findings are helpful when detecting deep vein thrombosis, and which findings are not helpful? >> Well, you know, I'd say really all findings are helpful. The critical message is that it's very important to do the history and physical and do it properly on patients who present with unilateral leg symptoms. There are some findings that have been incorporated in the clinical prediction rules which have had more importance than others, but it's important to elicit all the history and physical findings because this will lead you to determine whether an alternative diagnosis might be more likely.
So, for example, a Baker's cyst or cellulitis or a musculoskeletal injury or superficial phlebitis. So really, everything is helpful. It's putting them altogether which is the critical thing for making a proper diagnosis, and for that we usually use a clinical prediction rule. >> What factors go into the simplified clinical prediction rule? >> Well, there are a few rules that have been published. The one that our group has published, which has been described as the Wells model, has the following characteristics; active cancer, which would score a point in the model; paralysis, paresis, or recent plaster immobilization of the lower extremity, which scores a point; recently bedridden for three or more days or a major surgery within the previous 12 weeks scores a point; localized tenderness along the distribution of the deep venous system is another point; the entire leg being swollen scores a point.
And it's important here to note that this shouldn't be just observation, but the leg actually should be measured because it's very difficult to know by just looking at a leg whether there's swelling or not. Calf swelling measured 10 centimeters below the tibial tuberosity that demonstrates at least 3 centimeters increase in circumference compared to the asymptomatic extremity scores a point; pitting edema scores a point; the formation of collateral superficial, and I'm talking about non-varicose veins, so new veins that are formed on the extremity as basically bypassing an obstruction score a point; and from a history point of view, previously documented deep vein thrombosis scores a point.
But very important in the model as well, and which is what I was alluding to above, or before, is that an alternative diagnosis at least as likely as deep vein thrombosis scores minus two. So it's important to put all of these things into context, add up the patient's score and then you assign a probability assessment. >> How do you use the rule to assign patients to high, moderate or low probability groups? >> Well, in the original description of our rule, what we used was a score of zero or less would be low probability; one or two would be moderate, and three and above is high probability, but we've also used a designation of likely and unlikely, and unlikely is a score of one or less, and likely, a score of two or more.
>> I understand that there's a table in the chapter on deep vein thrombosis in the Rational Clinical Exam, table 18-7, that illustrates this quite well? >> That's correct. >> Do the D-dimer results without regard to the prediction rule ever change the probability of thrombus so much that further imaging becomes unnecessary? >> Well, I guess the simple answer to that is no, D-dimer should not be used in isolation without clinical assessment. >> Are there caveats to the decision to order a D-dimer in the first place or in the way clinicians should interpret the results?
>> Yes. The D-dimer, it's important for clinicians to appreciate that the D-dimer is a diagnostic tool, so it should not be used as a screening test. The clinical assessment should be made first, the history and physical, which we've been discussing, and then if in the physician's estimation it's still possible that the patient might have a deep vein thrombosis, so after that assessment they consider that a diagnostic possibility, then the clinical model should be applied and then a D-dimer is appropriately performed. But what's happening in some clinical situations is patients come through the door with leg symptoms, for example, in emergency departments, and the D-dimer is done automatically before the patient is even evaluated.
That's the incorrect way to use that diagnostic test. It should only be performed once the physician has made a determination they think deep vein thrombosis is a diagnostic possibility. >> What are the reference standard tests for deep vein thrombosis? >> Well, all of our textbooks describe contrast venography as the reference standard test, but in reality, that test is rarely done now. It's invasive, it requires the use of dye, expensive equipment. And the standard test has really become compression ultrasound.
>> Is there anything else you would like to tell our listeners about diagnosing deep vein thrombosis? I know one thing that might occur to people is we often hear about having had a recent long airplane flight might be related to developing a DVT. >> There are risk factors which people talk about that do slightly increase risk for deep vein thrombosis. Air travel is one, but it's a very minor risk factor when you think about the numbers of patients who travel. I think the latest data suggests that one patient in every 6,000 flights will develop a deep vein thrombosis as a consequence of that flight.
So it's a minor risk factor. Oral contraceptive pill has been considered a risk factor. But again, in the context of other risk factors, it's not as big a factor and it shouldn't sway the physician's decision one way or another. You should head more on these other factors that I mentioned above. The other thing I just implore physicians to do is to listen carefully to the patient, and then you apply these rules properly. And the other thing that I always try to make a point of is make sure that the ultrasound findings, when patients have gone for an ultrasound, make clinical sense.
These are diagnostic tests and false positives can occur, especially in patients who are at low or unlikely probability, and so when you see a patient with a low probability or unlikely probability with a positive ultrasound, think twice about whether that ultrasound result might be a false positive. So, for example, if it's a really small blood clot, keeping in mind that most DVTs are quite extensive and fill the entire vein up, that may be an old clot or a physiological clot after a catheter had been inserted, say, in the femoral vein. So ultrasound findings which suggest a clot may be a false positive include isolated small DVTs, nonocclusive DVT, a clot that has not started in the calf veins, except in the case of pregnant women, where it will start not infrequently in the iliac veins.
Or if the clot is highly echogenic on ultrasound. All these should point to the possibility that this may not be a fresh, acute DVT and the physician should delve into the problem a little more carefully and have a discussion with the diagnostic imaging expert. >> Thank you, Dr. Wells, for this overview of deep vein thrombosis. >> My pleasure. >> And for additional information about this topic, JAMAevidence subscribers can consult the online chapter on this topic in the Rational Clinical Examination.
This has been Joan Stephenson of JAMA talking with Dr. Philip Wells about deep vein thrombosis for JAMAevidence.
Segment:0 .
>> I'm Joan Stephenson, Editor of JAMA's Medical News and Perspectives section. Today I have the pleasure of speaking with Dr. Philip Wells about deep vein thrombosis. Dr. Wells, why don't you introduce yourself to our listeners. >> Okay. Hello there. My name's Dr. Phil Wells. I'm Professor, Chair and Chief of the Department of Medicine at the University of Ottawa. >> And, Dr. Wells, what do we know about the prevalence of deep vein thrombosis, and are there important demographic characteristics? >> So I guess more commonly we talk about incidents rather than prevalence, so the incidents is about one in a thousand per year, which interestingly, is about one in 150 per year in patients who are over 70 years of age.
With respect to prevalence, that depends on the population that's being studied, but in general, in an ultrasound department, about 15% of patients who are referred for a query of deep vein thrombosis will have that diagnosis made. The important demographic characteristics I would say are that it is more common in older people, it's more common in males, cancer patients and patients who are post-major surgery or after major trauma. >> Which symptoms increase the probability of deep vein thrombosis?
>> Well, it's a constellation of symptoms and signs and history that are really most important, but I think some of the symptoms that are particularly important to be aware of are to start with the fact that it's generally unilateral in the symptoms, and the specific ones that are of importance are probably mostly edema, a duskiness to the extremity, swelling, of course, which goes along with the edema, a description of pain which fits in a distribution of the deep vein pathway within the leg, and sometimes you actually will see, and the patients will complain of the formation of new veins, which we call collateral veins on the surface of their skin.
>> Which history and physical examination findings are helpful when detecting deep vein thrombosis, and which findings are not helpful? >> Well, you know, I'd say really all findings are helpful. The critical message is that it's very important to do the history and physical and do it properly on patients who present with unilateral leg symptoms. There are some findings that have been incorporated in the clinical prediction rules which have had more importance than others, but it's important to elicit all the history and physical findings because this will lead you to determine whether an alternative diagnosis might be more likely.
So, for example, a Baker's cyst or cellulitis or a musculoskeletal injury or superficial phlebitis. So really, everything is helpful. It's putting them altogether which is the critical thing for making a proper diagnosis, and for that we usually use a clinical prediction rule. >> What factors go into the simplified clinical prediction rule? >> Well, there are a few rules that have been published. The one that our group has published, which has been described as the Wells model, has the following characteristics; active cancer, which would score a point in the model; paralysis, paresis, or recent plaster immobilization of the lower extremity, which scores a point; recently bedridden for three or more days or a major surgery within the previous 12 weeks scores a point; localized tenderness along the distribution of the deep venous system is another point; the entire leg being swollen scores a point.
And it's important here to note that this shouldn't be just observation, but the leg actually should be measured because it's very difficult to know by just looking at a leg whether there's swelling or not. Calf swelling measured 10 centimeters below the tibial tuberosity that demonstrates at least 3 centimeters increase in circumference compared to the asymptomatic extremity scores a point; pitting edema scores a point; the formation of collateral superficial, and I'm talking about non-varicose veins, so new veins that are formed on the extremity as basically bypassing an obstruction score a point; and from a history point of view, previously documented deep vein thrombosis scores a point.
But very important in the model as well, and which is what I was alluding to above, or before, is that an alternative diagnosis at least as likely as deep vein thrombosis scores minus two. So it's important to put all of these things into context, add up the patient's score and then you assign a probability assessment. >> How do you use the rule to assign patients to high, moderate or low probability groups? >> Well, in the original description of our rule, what we used was a score of zero or less would be low probability; one or two would be moderate, and three and above is high probability, but we've also used a designation of likely and unlikely, and unlikely is a score of one or less, and likely, a score of two or more.
>> I understand that there's a table in the chapter on deep vein thrombosis in the Rational Clinical Exam, table 18-7, that illustrates this quite well? >> That's correct. >> Do the D-dimer results without regard to the prediction rule ever change the probability of thrombus so much that further imaging becomes unnecessary? >> Well, I guess the simple answer to that is no, D-dimer should not be used in isolation without clinical assessment. >> Are there caveats to the decision to order a D-dimer in the first place or in the way clinicians should interpret the results?
>> Yes. The D-dimer, it's important for clinicians to appreciate that the D-dimer is a diagnostic tool, so it should not be used as a screening test. The clinical assessment should be made first, the history and physical, which we've been discussing, and then if in the physician's estimation it's still possible that the patient might have a deep vein thrombosis, so after that assessment they consider that a diagnostic possibility, then the clinical model should be applied and then a D-dimer is appropriately performed. But what's happening in some clinical situations is patients come through the door with leg symptoms, for example, in emergency departments, and the D-dimer is done automatically before the patient is even evaluated.
That's the incorrect way to use that diagnostic test. It should only be performed once the physician has made a determination they think deep vein thrombosis is a diagnostic possibility. >> What are the reference standard tests for deep vein thrombosis? >> Well, all of our textbooks describe contrast venography as the reference standard test, but in reality, that test is rarely done now. It's invasive, it requires the use of dye, expensive equipment. And the standard test has really become compression ultrasound.
>> Is there anything else you would like to tell our listeners about diagnosing deep vein thrombosis? I know one thing that might occur to people is we often hear about having had a recent long airplane flight might be related to developing a DVT. >> There are risk factors which people talk about that do slightly increase risk for deep vein thrombosis. Air travel is one, but it's a very minor risk factor when you think about the numbers of patients who travel. I think the latest data suggests that one patient in every 6,000 flights will develop a deep vein thrombosis as a consequence of that flight.
So it's a minor risk factor. Oral contraceptive pill has been considered a risk factor. But again, in the context of other risk factors, it's not as big a factor and it shouldn't sway the physician's decision one way or another. You should head more on these other factors that I mentioned above. The other thing I just implore physicians to do is to listen carefully to the patient, and then you apply these rules properly. And the other thing that I always try to make a point of is make sure that the ultrasound findings, when patients have gone for an ultrasound, make clinical sense.
These are diagnostic tests and false positives can occur, especially in patients who are at low or unlikely probability, and so when you see a patient with a low probability or unlikely probability with a positive ultrasound, think twice about whether that ultrasound result might be a false positive. So, for example, if it's a really small blood clot, keeping in mind that most DVTs are quite extensive and fill the entire vein up, that may be an old clot or a physiological clot after a catheter had been inserted, say, in the femoral vein. So ultrasound findings which suggest a clot may be a false positive include isolated small DVTs, nonocclusive DVT, a clot that has not started in the calf veins, except in the case of pregnant women, where it will start not infrequently in the iliac veins.
Or if the clot is highly echogenic on ultrasound. All these should point to the possibility that this may not be a fresh, acute DVT and the physician should delve into the problem a little more carefully and have a discussion with the diagnostic imaging expert. >> Thank you, Dr. Wells, for this overview of deep vein thrombosis. >> My pleasure. >> And for additional information about this topic, JAMAevidence subscribers can consult the online chapter on this topic in the Rational Clinical Examination.
This has been Joan Stephenson of JAMA talking with Dr. Philip Wells about deep vein thrombosis for JAMAevidence.
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