Dr. Woodward's Aphorism: Ode to Strange and Unfamiliar Hoofbeats

By Rick Rader, MD, FAAIDD, FAADM, Editor-in-chief, Helen Journal

''How fast does a zebra have to run until it looks gray?

Readers of HELEN Journal who follow my monthly ramblings know that I often get my inspiration from old rock-n-roll songs from the fifties as I am driving to work.

This morning, I'm driving to work and hear The Cadets and their 1957 song, ''Stranded in the Jungle.'' While it did cause my fingers to slap the sides of my steering wheel, it did not connect me to anything related to the disability community.

Later that morning I read a news article that sealed the connection.

It seems that a Chinese zoo had come under scrutiny after admitting to painting donkeys black and white to look like zebras in a bid to increase tourist visits. An article in the New York Post reported, “the Zibo City amusement park in Shandong province caught the ire of Chinese social medial users after they noticed that the donkeys looked rather odd.''

The idea that a zebra could serve to encourage me to provide some musings about ways in which we can improve the clinical outcomes of people with intellectual disabilities could have some of you scratching your heads.

But it wasn't the song or the newsclip that encouraged me to say, ''Oh yeah, the old zebra lesson.''

It was the clever aphorism coined in the late 1940s by Dr. Theodore Woodward, a professor at the University of Maryland School of Maryland, who instructed his medical interns: ''When you hear hoofbeats behind you, don't expect to see a zebra.'' Other versions of it were, ''When you hear hoofbeats, think of horses, not zebras.'' 

The anal retentive medical historian in me actually discovered his actual words:''Don't look for zebras on Greene Street,'' the street of the University of Maryland medical campus.

According to John Sotos in Zebra Cards; An Aid to Obscure Diagnoses (1991), ''by 1960, the aphorism was widely known in medical circles.  The saying is a warning against the statistical base rate fallacy where the likelihood of something like a disease among the population is not taken into consideration for an individual.''

“It was the clever aphorism coined in the late 1940s by Dr. Theodore Woodward, a professor at the University of Maryland School of Maryland, who instructed his medical interns: ‘’When you hear hoofbeats behind you, don’t expect to see a zebra.’’ ”

While the zebra dilemma is applicable to all patient populations, one could argue that in individuals with intellectual and developmental disabilities the ''stripes'' promote additional challenges, confusion, and consternation.

Our population may have difficulties in communicating, are prone to excessive diagnostic overshadowing, exhibit maladaptive expressions of pain and anxiety, have incomplete medical records, high staff turnover leading to inconsistent narratives, and physicians without the skills, experience, and confidence to treat people with IDD.  Add to that the recently revealed realization that physicians have a negative bias about the lives of people with disabilities, and you have the ''perfect storm'' to create a zebra stampede.

Disease presentations come in four flavors; each one offering an opportunity to questions about where the hoofbeats are coming from; and who is making them. We see Typical presentations of Typical diseases. Then, up the feeding chain, we see Atypical presentations of Typical diseases. Moving up the complexity ladder is the Typical presentations of Atypical diseases; and the big enchilada is the Atypical presentation of Atypical diseases, the one you hope will never land at your door.  All looking like a TV game show with four tiles to flip over.

Dr. A. McGehee Harvey, writing in Differential Diagnosis (3rd ed., 1979). reads us the diagnostic riot act, ''In making the diagnosis of the cause of illness in an individual case, calculations of probability have no meaning.  The pertinent question is whether the disease is present or not.  Whether it is rare or common does not change the odds in a single patient.  If the diagnosis can be made on the basis of specific criteria, then these criteria are either fulfilled or not fulfilled.''

ThriveAP, a company focused on educating advanced practice providers, contributes this to the lyrical saga of ''a horse is a horse, of course, of course, and no one can talk to a horse of course'' (thanks to the old TV Show about a talking horse named Mr. Ed).  ''As medical providers, we worry about missing zebras. Is your patient suffering from a migraine headache or do you have a case of pseudotumor cerebri on your hands?  Are you dealing with a simple case of a backache or multiple myeloma?  Your patient presents with persistent fever and all of the standard labs return labeled ‘normal.'  What could go wrong?''

Technology might help us decide if the hoofbeats are coming from a horse, a zebra, or often in the case of a patient with an intellectual disability, the dreaded unicorn. FindZebra is a promising search engine specializing in rare diagnosis.  Simply input the patient’s symptoms into the search bar, and a list of ''zebra'' diagnosis populates.

The astute clinician who questions ''normal'' lab results against the backdrop of the feeling that ''all is not right here,'' deserves to spend time in the Serengeti surrounded by a migrating herd of thousands of zebras; none of them feeling that they are either rare or puzzling. It is a game changer for sure.  It's in that setting that one can begin to wonder why the zebra developed stripes to begin with. Prevailing theories regarding the stripes include thermoregulation, camouflage that helps them hide from predators, and protection from biting flies.

While I wanted to share and celebrate the wisdom of Dr. Woodward's ''hoofbeats'' aphorism, there is another famous doctor who shared a valuable lesson we should all embrace: ''There's no limit to how much you'll know, depending how far beyond zebra you go.'' Thank you Dr. Seuss.

In celebration of the many zebras who have called attention to the notion of ''on the other hand,'' or ''could it be,'' and have inspired clinicians to trust their instinct and look closer, and look for more, we have designated January 31st as International Zebra Day.  In celebration of those African ungulates we might all want to wear stripes in their honor.

MEDICAL APHORISMS

While Dr. Woodward's ''Hoofbeats'' aphorism is a classic, here are some other medical aphorisms that could be of interest to clinicians, self-advocates, parents, educators and students.

SUTTON'S LAW - Perform first the diagnostic test expected to be most useful.

OCCAM'S RAZOR - Select from among competing hypotheses the one that makes the fewest new assumptions.

LEONARD'S LAW OF PHYSICAL FINDINGS - It is obvious or it is not there.

HICKAM'S DICTUM - ''Patients can have as many diseases as they damn well please.''

Rick Rader, MD, FAAIDD, FAADM, Editor-in-chief, Helen Journal