Thread by @AdamRodmanMD

Time for a Tweetorial! Though this will only be partially #histmed and mostly about philosophy. Inspired by @chrischiu -- so let’s talk about Occam’s Razor and Hickam’s Dictum!

But before we get going, let’s start with a little pre-test. Case #1. A young man presents with acute onset of severe fevers and chills, rhinorrhea, headache, confusion, and neck stiffness. What does he have?

And case #2, a middle aged woman presents to clinic with a nocturnal cough which she has had for a number of years. What is the most likely diagnosis?

Assuming you got those two questions right, congratulations! You’re using Occam’s razor! Occam’s Razor is classically stated as “Entia non sunt multiplicanda sine necessitate” -- entities are not to be multiplied without necessit

William of Ockham (NOTE: Occam is NOT his last name -- should technically be “William’s Razor”) was a Franciscan monk and Oxford lecturer in the early 14th century who invented his Law of Parsimony

An “entity” is a hypothetical construct. Therefore, if you have two competing ideas and one relies on extra hypothetical ideas, the simpler is better. He used his Law of Parsimony to savage many theological and philosophical ideas.

Which naturally led him to getting expelled from Oxford, dragged before the Pope, and excommunicated.

Occam’s Razor, as it became known in the late 19th century, has been adopted by scientists, mathematicians, atheists, and even prison reformers.

Einstein used it in justifying special relativity, and later said:

“Everything should be as simple as possible, but not simpler”

(like many Einstein quotes, though, it's paraphrased)

Of course, I'm more interested in medicine than special relativity, where Occam’s Razor has two major manifestations:

The first is “diagnostic parsimony” -- that is, if a patient’s symptoms can be explained by one unifying diagnosis, rather than several, that diagnosis is most likely to be correct.

Take Case #1. The constellation of fevers, HA, rhinorrhea, and neck stiffness can all be explained by a single diagnosis -- acute bacterial meningitis. Therefore, this would be preferred over the two diagnoses of influenza and torticollis.

The second manifestation is the famous saying, “When you hear hoofbeats, think horses, not zebras.” Or as it’s generally put, “Common things are common.”

In Case #2, all diagnoses can cause a nocturnal cough. However, esophageal reflux is by far and away the most common.

Occam’s razor was controversial in its own day, and there have been any number of “anti-razors” developed since. The most famous is from William’s contemporary, Walter Chatton.

Chatton’s anti-razor states, "If three things are not enough to verify an affirmative proposition about things, a fourth must be added, and so on."

In medicine, this takes the form of Hickam’s dictum (which appears to be apocryphal rhyming with Occam, though some have tried to attribute to John Hickam):

"A man can have as many diseases as he damn well pleases."

The other famous argument against “diagnostic parsimony” is Saint’s Triad, identified by South African surgeon CFM Saint --the fact that hiatal hernia, gallbladder disease, and diverticulosis often occur together.

He argued that there was no identified underlying cause of this triad; the patients truly appeared to have three different diagnoses.

So let’s take a quick poll -- which is more relevant to practicing medicine in the 21st century?

This will shock you, I'm sure, but I’m on Team C. Both Occam’s razor and Hickam’s dictum are useful mental heuristics in certain circumstances. A brief example:

Case #3. A 65 year-old man presents with a month history of a productive cough, and over the past three days, fever, chills, and now confusion and lethargy. What’s the most likely diagnosis?

Now case #4 -- exactly the same, except your 65 year-old patient has newly diagnosed HIV/AIDS with a CD4 of 14, and incredibly high viral load.

You can use both these contrary principles to help us approach similar patients. There are some patients where you would first use Ockham (like case #3), and others where you would first use Hickam (case #4).

Okay, I hope that was helpful! If you want to hear more about Occam’s Razor and Hickam’s dictum, I talk about it more in the latest episode of my podcast about Pierre Louis’ famous bloodletting trial: bedside-rounds.org/episode-38-blo…

(I also talk about Newton's Flaming Laser Sword -- if that tempts you more!) philosophynow.org/issues/46/Newt…

And if you’re interested in medical history and its intersections with culture and society, I host a medical podcast about that very topic. You can find it on iTunes, Stitcher, Spotify, or basically any podcast service. itunes.apple.com/us/podcast/bed…