Aortic Dissection: Still the Great Masquerader

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 Aortic Dissection: Still the Great Masquerader

Ask any trainee in emergency medicine for a list of rapidly fatal conditions, and it is almost certain that acute aortic dissection (AAD) will be near the top. In acute care medicine, AAD is a condition we think about multiple times per day.

Emergency medicine training is focused on such life threats; we are taught to think of the worst conditions first. Yet, AAD is still misdiagnosed frequently and it becomes a source of litigation on a regular basis. I take part in only a handful of legal case consultations annually, but I see cases of missed AAD heading for litigation every year.

The “classic” presentation of AAD is quite dramatic: sharp, ripping chest pain that is abrupt, with maximal intensity at its onset, radiating to the midscapular region. The classic patient at risk has the same risk factors as those for coronary artery disease, especially hypertension, and the patient typically presents quite hypertensive with pulse deficits and unequal blood pressures in the upper extremities. The chest radiograph shows a wide mediastinum. Patients with Marfan syndrome or other connective tissue diseases are also at risk. With such obvious presentations and risk factors, how can we be missing this condition?

A recent review in the British cardiology journal Heart very nicely summarized many of the reasons why AAD is difficult to diagnose in many cases. In this summary, I won’t review the basic aspects of pathophysiology, diagnosis, or treatment, but instead I’ll focus on why AAD is such a diagnostic conundrum.

The authors of this excellent review identify several main causes of diagnostic pitfalls:

  • Symptoms are variable and can be minimal. The “classic” presentation noted earlier is actually not typical. The pain with which patients present is often vague and poorly localized, and it may be localized to any location in the torso without the radiation to the mid-scapular region. Pain may also be minimal in intensity. Patients frequently do not present with excruciating pain, and in fact, studies indicate that patients who present walking into the emergency department are more frequently misdiagnosed. On the other hand, patients who present in extremis often cannot provide a good history, further confounding the diagnostic process.

  • The chest pain of AAD can mimic that of other, more common acute conditions, such as acute coronary syndrome, pulmonary embolism, pericarditis, and esophagitis; these are common initial misdiagnoses.

  • The symptoms of AAD often develop rapidly and evolve or change. As the intimal tear propagates, the intensity of the pain can wax, wane, and even migrate in location.

  • The typical first-line investigations, such as vital signs, chest radiograph, and ECG, are poorly sensitive and poorly specific. The “classic” pulse deficits and upper-extremity blood pressure differences are often absent. The mediastinum on x-ray is often normal in size, and the ECG may show signs of ischemia leading to a misdiagnosis of acute coronary syndrome.

  • There are no biomarkers specific to AAD. In fact, AAD may produce elevated troponin levels or D-dimer levels and mislead the practitioner into working up acute coronary syndrome or pulmonary embolism, respectively.

  • “Malperfusion syndromes” produced by AAD can easily lead practitioners to alternative diagnoses. Malperfusion refers to aortic branch vessel blockage from the dissection flap, producing ischemia to other areas of the body. For example:

    • If the dissection causes carotid occlusion, the patient can present with neurologic deficits, resulting in a misdiagnosis of stroke.

    • If the dissection propagates in a retrograde direction toward the heart, ECG findings of coronary ischemia can occur, including ST-segment depression or elevation, resulting in a misdiagnosis of acute coronary syndrome.

    • If the dissection causes occlusion or ischemia of visceral vessels, the patient may present with abdominal pain, resulting in a misdiagnosis of an abdominal condition.

    • If the dissection produces occlusion of an iliac vessel, the patient may present with lower limb ischemia, leading to a workup for arterial occlusion.

    • If the dissection causes occlusion of a renal artery, it may produce elevations in creatinine level, leading to a workup for acute kidney injury.

Patients can present with isolated symptoms of malperfusion (eg, isolated stroke symptoms, isolated abdominal pain, isolated syncope, isolated limb ischemia, and so on) in the absence of thoracic pain. In any of these cases, the practitioner may initiate a workup that leads them away from AAD.

Viewpoint

When speaking of thoracic aortic disease more than 100 years ago, William Osler stated that “there is no disease more conducive to clinical humility.” In contemporary times, AAD is often referred to as “the great masquerader” because it so frequently mimics other conditions, largely because of the malperfusion syndromes noted above.

Misdiagnosis is also common because of the absence of the “classic” symptoms and signs that we all learn in training. Given the lethality of this disease and the many reasons for initial misdiagnosis, it is no surprise that AAD frequently makes its appearance in the medical malpractice arena.

The authors of this article promote the use of an AAD risk score to assist in making this diagnosis, similar to the decision instruments that are often used in the evaluation of acute coronary syndrome and pulmonary embolism. These authors also endorse the use of D-dimer testing in the evaluation of AAD, despite its low specificity.

On the other hand, the 2015 American College of Emergency Physicians Clinical Policy in the Evaluation and Management of Adult Patients does not endorse the use of D-dimer testing or risk scores because of insufficient accuracy. Instead, it leaves the decision regarding whether to initiate the workup to clinician judgment. So, what is the bottom line?

After having read dozens of articles on AAD in search of a definite workup plan, I don’t have a simple, foolproof answer about who needs the workup. However, recalling that AAD frequently does not present classically, I would offer these few take-home points:

  • Consider the possibility of AAD in patients with pain in any area of the torso, not just those with pain in the chest or upper back.

  • Remember that the malperfusion syndromes of AAD will cause some of the unusual presentations described.

  • Accept the fact that we will miss some cases of AAD no matter how good we are.

  • For those practitioners who work in litigious environments, in patients with any type of torso pain, consider AAD in your differential diagnosis and document an appropriate history indicating that you considered the possibility of AAD.

In honor of William Osler, I’ll add one final take-home point: Be humble about this disease!

Amal Mattu, MD, is a professor, vice chair of education, and co-director of the emergency cardiology fellowship in the department of emergency medicine at the University of Maryland School of Medicine in Baltimore.

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