Pulmonary embolism
BMJ 2024; 384 doi: https://doi.org/10.1136/bmj-2022-071662 (Published 08 February 2024) Cite this as: BMJ 2024;384:e071662
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Dear Editor
In the vignette, increasing breathlessness was the "red flag" for raising the index of suspicion for pulmonary embolism (PE). However, in the context of coronary artery disease (also a feature in this case), pain-free myocardial infarction (giving rise to heart failure) could have been a plausible alternative cause of increasing breathlessness.
Ultrasonographic documentation of deep vein thrombosis (DVT) is the one feature that could distinguish between these two competing causes of increasing breathlessness. The more proximal the DVT, the greater the probability of its causal relationship with PE[1],[2], especially given the fact that DVT is associated with an Odds Ratio amounting to 1.9 (95% Confidence Interval, 1.23 to 2.95) in favour of the diagnosis of PE[3].
Whether or not the association of proximal DVT and breathlessness justifies a policy of prompt initiation of anticoagulant therapy without recourse to imaging with computed tomography and pulmonary angiography (CTPA)[4],[5] is a controversial issue justifying open debate, especially in view of the fact that, in the majority of patients characterised by the association of venous thromboembolism and a strong, transient, provoking factor, the duration of anticoagulant treatment is identical both for DVT and for PE[6]. On the one hand, however, there is a perception that we have a duty of care to mitigate exposure to radiation both for patients and for radiology staff[7],[8], especially in the childbearing age group. On the other hand, we have to recognise that the association of DVT and PE can be mimicked by the association of DVT and dissecting aneurysm of the aorta (DAA)[9], and that hypertension (which was also a feature in the vignette) can be a risk factor for pain-free worsening of breathlessness[10]. In the latter report transthoracic echocardiography was instrumental in the workup culminating in the diagnosis of DAA[10]. Accordingly, ultrasonography for DVT and echocardiography for suspected DAA should be included in the workup of suspected PE.
References
[1] Kohn H., Kooig B., Mostbeck A. Incidence and clinical feature s of pulmonary embolism in patients with deep vein thrombosis: A prospective study. European Journal of Nuclear Medicine 1987;13:S11-S15
[2] Tzoran I., Saharov G., Brenner B et al. Silent pulmonary embolism in patients with proximal deep vein thrombosis in the lower limbs. Journal of Thrombosis and Haemostasis 2012;10:564-571
[3] Miniati M., Bottai M., Monti S et al. Simple and accurate prediction of the clinical probability of pulmonary embolism. Am J Respir Crit Care Med 2008;179:290-294
[4] Konstntinides SAV., Torbicki A., Agnelli G et al. 2014 ESC Guidelines on the diagnosis and management of acute pulmonary embolism. The TASK force for the diagnosis and management of acute pulmonary embolism of the European Society of Cardiology. Eur Heart J 2014;35:3033-3080
[5] Hull CM., Hopkins CL., Purdy NJ., Lloyd RC., Harris JA. A case of unprovoked venous thromboembolism in a marathon athlete presenting atypical; sequelae; what are the chances. Scandinavian J Med Sci Sports 2015;25:699-705
[6] Duffett L., Castelucci LA., Firgie MA. Pulmonary embolism: update on management and controversies. BMJ 2020;370:m2177 doi:10.1136/bmj.m2177
[7] Gill MK., Vijayanathan A., Kumar G. Use of 100 kV in computed tomography pulmonary angiography in the detection of pulmonary embolism: effect on radiation and image quality. Quant Imaging Med Surg 2015;5:524-533
[8] Jolobe OMP. Palla's sign and the challenge of optimizing the imaging strategy in patients with high pretest probability of pulmonary embolism. QJMed 2021 doi.org/10.1093/qjmed/hcab322
[9] Moromoto S., Izumi T., Sakurai T et al. Pulmonary embolism and deep vein thrombosis complicating acute aortic dissection during medical treatment. Internal Medicine doi:10.2169/internalmedicine.46.6215
[10] Ayrik C., Cece H., Aslam O., Karcioglu O., Yilmaz E. Seeing the invisible: painless aortic dissection in the emergency setting. Emerg Med J 2006;23:e24
Competing interests: No competing interests
Positive predictive values do not inform comparative diagnostic exercises
Dear Editor,
I was interested to read Maughan and colleagues’ education piece on pulmonary embolism, particularly the factors that predict a delayed diagnosis and the impact of early anticoagulation.
I would like to draw attention to the use of positive likelihood ratios when describing elements from the patient history and examination in this article.
In a defined population, the positive likelihood ratio describes the proportion of patients with a positive finding (such as “patient has dyspnoea”) that are subsequently diagnosed with pulmonary embolism, divided by those with the finding who have an alternative diagnosis (1).
However, likelihood ratios consider all potential diagnoses, and cannot inform a comparative diagnostic exercise between the relatively few competing differentials that remain after history taking and examination. Furthermore, positive predictive values rarely allow us to exclude a diagnosis with confidence; a necessary part of the diagnostic process.
For example, even if the positive likelihood ratio is very high, a finding such as “syncope” may not help the diagnostician distinguish between differentials, such as pulmonary embolism and myocardial infarction.
Additionally, likelihood ratios apply only to a defined population. The parameters of this population are not defined in the article, though perhaps we may infer from author affiliations that these ratios apply to emergency department attendees. Such information should be clarified for the benefit of the reader.
1. Llewelyn H, Ang AH, Lewis K, Abdullah A. The Oxford Handbook of Clinical Diagnosis. 2nd ed. Oxford University Press, 2009:754-60
Competing interests: No competing interests