The Medical History as an Exposure Narrative: A Didactic for Medical Students and Young Physicians

I just received an email from a medical student on the other side of the pond asking for my advice for junior doctors for learning the practice of medicine.  I will oblige.  When students are taught how to take a medical history, they are taught a rote sequence and its components, but are not taught what the point really is, why we ask certain questions, how we string the answers together, which components need more or less emphasis in a given case.  Here I will present a framework for that understanding, which may make history taking more meaningful and useful for those learning and refining it.

What we are really trying to do with history taking is to make a narrative of the patient's exposures in his or her environment.  This exposure narrative allows us to use Bayes' Theorem to determine the most likely causes for a given chief complaint.  Bayes Theorem should be reviewed for its own sake in order to understand its use here and elsewhere, but simply understanding that the base rate of a disease in a certain population is the "prior probability" of that disease in a patient will suffice for now.  So, if I asked you what mammal you are likely to see on your hike in the Rocky Mountains, you will list squirrel and deer and elk before mountain lion and badger.  It's just common to see deer and elk there.  In the jungle, or the desert, the answers would be different - because different animals have different probabilities in different environments.  Likewise, when a 70-year-old comes with pain in the joints, osteo- and rheumatoid arthritis are more likely than lupus and juvenile rheumatoid arthritis, which would have higher probabilities in younger patients.  Thus, age is an exposure, perhaps one of the most important ones, and this is why a student's presentation often begins with something like "Mr. Jones is a 78-year-old man..."  (It is also why I frequently interrupt physicians who call me to admit a patient or consult on one, because I can't begin to order the probabilities until I know the age of the patient, which they frequently omit because of indolence.)  The older person has been exposed to wear and tear on the body for a longer time, and this figures prominently in the probabilities of the diseases that s/he is likely to have.

Antifragile but Exposed: A Framework for Understanding Disease that Can Improve Diagnostic Decision Making

Ruination IPA by Stone

It is said that the history reveals the diagnosis 90% of the time, but it is not stated why this is so.  Herein I will explain the logic behind this aphorism.

I used to tell residents that most of the time, the diagnosis is something common, or something related to something we already know the patient has.  In addition, when teaching history taking, I told the medical students to view history taking as an exercise in determining what the patient is exposed to in his or her environment, for these exposures weigh on the probabilities of potential diagnoses.  These principles explain the basis of the history aphorism.

Nassem Nicholas Taleb was right in his book Antifragile - evolution has made our species beyond robust - antifragile, a term which he coined.  We resist disease, we repair injury, we get stronger when exposed to stress (the antifragile principle).  But there are ailments that humans suffer for which evolution has not worked out a defense or a solution, or those which result because evolution is helping the same organisms which attack us become antifragile just as it selects us for antifragility.  This is why infectious maladies are at the top of the list for adult (and I suspect pediatric) internal medicine admissions.  Pneumonia, UTI, URI, etc.