What's with all the Zebras?

What's with all the Zebras?

Rare Disease Day is among us! On Thursday, February 28th, the rare disease world will ring loud for all to hear. Tell your friends! Tell your family! Tell the world to raise awareness for rare diseases.  Snap a pic and show us your #Perthesstripes

The iconic zebra and the rare disease…

You may have noticed rare diseases are often associated with the zebra. Why the zebra, you may ask. A unicorn is certainly more unique (and trendy at the moment). And if not limited to the animal kingdom, a blue moon usually signifies a pretty unique event, or a shooting star.

Well, in the medical field a rare disease, disorder, condition, or syndrome is termed a “zebra.” This slang which is now ubiquitous is credited to the teachings of a University of Maryland physician and professor “Physical Diagnosis,” Dr. Theodore Woodward who cautioned his interns, “When you hear hoofbeats, think of horses not zebras.”

Dr. Woodward (1914-2005) was a talented physician whose career included work in infectious disease worldwide as well as in medical education. He received accolades and awards President Roosevelt, the U.S. Army, the Japanese Ministry of Health, and the American College of Physicians just to name a few. Dr. Woodward continued seeing patients and teaching into his eighties. Being from Maryland, horses would have been common while zebras, less so.

The analogy of the Zebra…

Dr. Woodward was simply advising diagnosticians not to jump to bizarre conclusions when the most likely diagnosis is often the most common one. The human mind tends to jump to the more memorable events and code them as more common or more likely than they really are. This is a basic mental shortcut or bias and is termed the availability heuristic and it occurs in all of us all the time. Have you ever waited in line for the microwave at work as your coworker heated up a very fragrant salmon dish and thought “Ugh, Frank again; always stinking up the place with salmon.” That’s basically the availability heuristic at work.  

The differential diagnosis and the rare disorder…

Since we’re reading this relative to a rare disease, you might think erring on the side of caution isn’t a bad thing. It’s good for a practitioner to keep an open mind, or differential diagnosis. However, if every patient who walked in the door with a runny nose was worked up as if they had Tuberculosis, the patient’s common cold would resolve before all their tests came back ruling out TB. The patient and their family would encounter unnecessary stress as well as medical expenses. You might be thinking “why TB; no one has had that since Doc Holliday.” Great point. Did you know cerebrospinal fluid can leak from your brain out your nose (or ear)? Yep. It can. Lots of things and no reason to get all worked up over it because that runny nose is most likely a common cold.


Sometimes the diagnosis or treatment just doesn’t fit. That’s when perseverance on the part of the patient/parent and clinician is necessary. When the common diagnosis has been ruled out or the common treatment just isn’t helping, it may in fact be a rare disease. Patience and advocacy play a big part here. Many rare disorders are diagnoses of exclusion, meaning you have to suffer through proving that something “isn’t” before you can decide that it is. The process can be arduous and frustrating. You can help by advocating for your Perthes warrior and all those dealing with rare disorders by talking about these disorders. Advocate for those you love. Educate others on what it takes to manage a disease or disorder that no one knows much about. Explain what it means and how hurtful it can be to hear “you don’t look sick.”

Share a post! Take a pic! Explain to the world what it means to have a rare disease. Explain to the world what it means to be a zebra!  

Source and Photo Credit: Mackowiak PA. THEODORE E. WOODWARD: 1914–2005. Transactions of the American Clinical and Climatological Association. 2006;117:lxviii-lxxi.

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