An upside-down cake: the EM differential diagnosis

An upside-down cake: the EM differential diagnosis

How we’re different

When I was rotating on surgery as a medical student, our attending once asked of our small group what may be concerning in the differential for right upper quadrant abdominal pain. A very eager and a somewhat brash student blurted immediately: “Echinococcal cyst!” The attending replied, “Well, that’s true, but if Echinococcal cyst is the first thing you think of as a surgical consultant, you’re crazy!”

On the other hand, take a practicing internal medicine physician like my Dad. He formulates his differentials with a very different strategy, which is: what is the most likely? A chronic cough is bronchitis (even with hemoptysis), pneumonia, GERD or postnasal drip. Shoulder pain is, of course, a sprain, bursitis, or some referred cervical impingement. And so on.

Unfortunately, neither hunting for zebras (an unofficial US name for exciting but rare diagnoses) nor settling for the most common works for emergency medicine. In fact, that is how true diagnoses may get missed and patients may start dying. 

Why we are different

The EM differential diagnosis is a pyramid tipped on its head. It is therefore different from how differentials are approached by many other specialties.

In EM, we first have to think of and rule out the most severe or threatening pathology. That’s a given. But our choices have to come from among the common killers, not Martian viruses or unheard of tumors from a medical encyclopedia. 

Amoebic meningitis is exciting to encounter in your practice. But guess what? Your patient won’t have it. At the same time, for EM physicians things like pulmonary embolus, aneurysm of the abdominal aorta, subarachnoid hemorrhage and necrotizing fasciitis are everyday icons on our cognitive desktops. While less common than a common cold, these things are by no means rare.

Why it is difficult

In EM, one can rest assured that common pathology will present atypically and not quite like the textbook.

Things are further complicated by confounders, mimics and the disjunction of concern.
 
Confounders are concurrent pathologic processes that the patient already has, which tend to get worse due to any new significant disease process or general body stress. CHF and COPD get exacerbated, kidneys become insufficient, anxiety and psychoses go florid and atrial fibrillation accelerates to rapid. How do you spot sepsis or an MI, which is the true cause of it all, underneath layers and layers of abnormal vitals and test results?
 
Mimics are things that pretend to be other diseases. PE presenting with a low-grade fever and a cough, carbon monoxide poisoning posing as geriatric altered mental status, and severe sepsis arriving as chest pain, dizziness and a bumped troponin. Such has happened many times in the past and continues to happen daily at all EDs globally.
 
The disjunction of concern is when your patient is not worried about what you are worried about. They don’t want to get cancer like their neighbor, but they have never heard of a TIA or an AAA. Kawasaki disease? Why don’t you just give my daughter better antibiotics? My uncle died of a heart attack at 35, not a “bisection” or whatever you called it…So I don’t want a CT scan!
 
An EM physician’s focus on ruling out worst-case scenarios may paradoxically contribute to a patient’s distrust at the end of the encounter. The patient’s agenda is to leave knowing what disease they have, while we are often satisfied knowing which horrible things a patient does do not have.

It may take years of practice to be able to persuade someone that you have done due diligence and your professional duty by excluding a whole lot of deadly things, while the exact diagnosis still remains elusive.

Secretly paranoid, openly confident and always nice

We are confident, but also afraid. We have to think of the worst yet possible scenario for any complaint, yet of course anticipate that the actual diagnosis will hopefully be something less severe and quite common – like a migraine. After all, after most CT scans and lumbar punctures, it is not a subarachnoid hemorrhage.

In EM, we are in this perpetual struggle with having to be professionally pessimistic and paranoid on the one hand, yet emotionally supportive and reassuring for the patient on the other. I always teach my students, even nursing trainees, that no one should be leaving an emergency department more scared or anxious than when they came in.

Your job as a rotating trainee in EM is to understand and learn this exact interplay.

Homework

For your attending, but more importantly for yourself and your patients, you have to be as concerned with sepsis from PID on a 16-year-old young woman with fever and abdominal pain as you are with appendicitis. The 86 year old grandmother with Afib but on no anti-coagulation, because she falls a lot is not just TIA or CVA prone. Her embolic clots may just as well be traveling downstream, causing that intermittent or out of proportion abdominal pain called mesenteric ischemia – for which you do not have a good lab test or imaging, by the way.

Here is a brief checklist:

  • For any anatomic complaint or a chief complaint type

    think of several real worst-case scenarios that are not zebras. Can something horrible yet by no means unheard of be presenting atypically? What steps can you take to prove or disprove it?

  • Think of confounders and mimics.

    What else could be going on? Like a stack of dominoes: what happened first, what happened next?

  • Address the patient’s concerns

    while carefully and patiently pursuing your own professional agenda.

  • When it turns out to be something common or benign,

    don’t forget to discuss worrisome signs for which to return. What if you’re still wrong?

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Cite this article as: Anthony Rodigin, "An upside-down cake: the EM differential diagnosis," in International Emergency Medicine Education Project, August 26, 2019, https://iem-student.org/2019/08/26/an-upside-down-cake-the-em-differential-diagnosis/, date accessed: November 11, 2019

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