Monday, 30 March 2015

Overdiagnosis: in relation with pulmonary embolism

The introduction of computed tomographic pulmonary angiography (CTPA) for the diagnosis of pulmonary embolism, according to a study published in JAMA Internal Medicine (US data), has been associated with an increase of 80% in the incidence of pathology (from 62.1 to 112.3 per 100,000 population p<0.001), with a reduction in hospital mortality of 35% (from 12.1% to 7.8% p<0.001), which lamentably only has led to a decrease in mortality rates of 3% (from 12.3 to 11.9 deaths per 100,000 p=0.02) and also lamentably, an increase in presumed complications of anticoagulation therapy of 71% (from 3.1% to 5.3% per 100,000 p<0.001).

In the graph below, taken from the article, you can see the behaviour of the incidence of pulmonary embolism in relation to mortality, both population-based, comparing the 1993-1998 period, prior to the introduction of CTPA, with the subsequent one. The overall incidence (bright blue) includes all patients admitted to the hospital for any medical or surgical circumstance. The percentages represent average increases for each year (APC: Annual Percentage Change).

A recent article published in BMJ by the same authors of the JAMA Internal Medicine states: "For decades doctors have learned that pulmonary embolism is a very significant event in the life of patients and therefore they know to be very careful. The doctors always want to avoid allowing the silent murderer to escape and for this reason, CTPA has become a very popular diagnostic tool to more effectively inspect the hidden iceberg territories. Therefore, the willingness of physicians with the indication of CTPA is excellent, to which we must add that radiologists also like the technique, let alone the device designers and pharmaceutical anticoagulant manufacturers."

More elements in favour of the overdiagnosis thesis (suspect, although not definitive data)

The "casual" findings in studies using CT angiography for other purposes give the following results of pulmonary embolism cases found unintentionally: 16% in mechanically ventilated patients, 17% in hospitalized patients older than 80 years, 20% in trauma patients and up to 60% in autopsy studies.

A study of 192 patients with subsegmental pulmonary embolism found no difference in recurrences, nor in complications nor in mortality in the group of 65 untreated patients compared to the group of 127 anti-coagulated patients. We must clarify that this study was not a clinical trial because the decision was discretionary on the part of physicians.

I have not said it before, but the BMJ article title is: "When a test is too good; when CTPA discovers pulmonary embolism that would have been better ignored". I think that this header defines very well the change of mentality that we doctors are facing today and for which we are not prepared.

Unresolved issues: the fight against overdiagnosis should go beyond the "complaint". We must create a new way of thinking and doing, for which we must develop specific clinical guidelines to alleviate the phenomenon as the researchers in the cited articles are doing, but we also have to learn to pose "relevant" questions for new research such as: What is the natural course (and forecast) of subsegmental pulmonary embolism?

Jordi Varela


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