February 11, 2014
1 min read

History is a diagnostic test

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A teenage boy entered our hospital in respiratory distress. He was chronically ill due to an underlying medical disorder, leaving him with decreased respiratory reserve. He was febrile and tachypneic, with bilateral infiltrates on chest radiograph and chest CT. His CRP was highly elevated with a left-shifted white blood cell count. He rapidly progressed from needing nasal cannula to high-flow nasal cannula followed by CPAP. For any physician who relies on pattern recognition, this patient had bacterial pneumonia. Antibiotics were initiated, and he was admitted to the ICU.

On consultation, however, his history gave away his diagnosis. The patient had been afebrile and quite well that morning. He boarded a bus to school, and the bus stopped short. He had underlying bone disease, so he suffered fractures of his tibia, fibula and femur from falling during this bus accident. Within 4 hours of his fracture, he developed respiratory distress. He had no preceding upper respiratory infection, rhinorrhea, cough or congestion. Over his first 24 hours of admission, his chest radiograph blossomed into diffuse bilateral fluffy infiltrates. He had drops in his hemoglobin and platelets. He had a classic case of fat emboli, not community-acquired pneumonia.

However, his antibiotics were not stopped. Some clinicians felt that while fat emboli was his most likely diagnosis, we could not rule out bacterial pneumonia, so we were obligated to treat based on his chest X-ray. I would argue, somewhat facetiously, that we almost NEVER rule out bacterial pneumonia with diagnostic tests on patients with abnormal chest X-rays, yet we have been willing to diagnose those patients with viral pneumonitis, chronic lung disease or peribronchial thickening due to asthma. Why did physicians lack confidence in the diagnosis here?

I suspect that it is because the diagnosis of fat emboli is rare. We work in a children’s hospital, and we almost never see this condition. However, we have to remember that history is frequently a sufficient diagnostic test that allows you to rule out common conditions, like bacterial pneumonia. The rarity of this patient’s true condition does not negate the reliability of the history. And, conveniently, taking a history is basically free.