Increase in CT Scans Linked to Emboli Overdiagnosis

They found that ventilation-perfusion (VQ) scanning, introduced in the mid-1960s, was until recently the first line test for PE. But the introduction in 1998 of multidetector CT pulmonary angiography, which offers higher resolution and more definitive results, has resulted in a 14-fold rise in CT with a concomitant 52% decrease in VQ scanning.

But the combination of a large increase in incidence, reduced case fatality (in-hospital deaths among people with a diagnosis of PE), and a minimal decrease in mortality (deaths from PE in the population) suggests to the researchers that many of the extra emboli being detected are not clinically important. However, the harms from overdiagnosis are real, resulting from a substantial increase in complications from anticoagulation treatments and anxiety and inconvenience for patients following diagnosis and treatment.

The researchers added that the symptoms and signs of PE, i.e., shortness of breath, pleuritic chest pain, tachycardia, and signs of right heart strain, are neither sensitive nor specific, and have led to the creation of scoring systems to determine which patients should receive a scan, although many clinicians simply proceed with imaging to confirm or refute the diagnosis. The authors cautioned that the alternative to sensitive testing with overdiagnosis is not to test less, but to test and treat more selectively and to also consider alternative forms of testing, such as ventilation-perfusion scanning and ultrasonography. The study was published on July 2, 2013, in BMJ.

“Although there was an 80% increase in incidence of pulmonary emboli from 1998 to 2006, age-adjusted deaths from pulmonary emboli dropped by a third, suggesting that the extra pulmonary emboli being detected are less lethal,” concluded lead author Renda Soylemez Wiener, MD, of BUMC, and colleagues. “More nonfatal pulmonary emboli dilute case fatality but do not change mortality.”

The widespread availability of CT pulmonary angiography has encouraged doctors to lower their threshold for looking for PE, resulting in extra diagnoses that lead to testing even more patients because of the pervasive belief that finding even a tiny, subsegmental PE means you may have saved a life. Case finding has also increased as a result of the widespread use of nonspecific blood tests which raise suspicion of PE in patients in whom it would not otherwise have been considered. Concerns about accusations of malpractice may also increase the use of CT pulmonary angiography, as can commercial interests fuelling imaging rates.

Related Links:
Boston University School of Medicine
Dartmouth Medical School