Zebra is the American medical slang for arriving at an exotic medical diagnosis when a more commonplace explanation is more likely.[1] It is shorthand for the aphorism coined in the late 1940s by Dr. Theodore Woodward, professor at the University of Maryland School of Medicine, who instructed his medical interns: "When you hear hoofbeats, think of horses not zebras".[2] Since horses are common in Maryland while zebras are relatively rare, logically one could confidently guess that an animal making hoofbeats is probably a horse. By 1960, the aphorism was widely known in medical circles.[3] 
 
 As explained by Sotos,[4] medical novices are predisposed to make rare diagnoses because of (a) the availability heuristic ("events more easily remembered are judged more probable") and (b) the phenomenon first enunciated in Rhetorica ad Herennium (circa 85 BC), "the striking and the novel stay longer in the mind." Thus, the aphorism is an important caution against these biases when teaching medical students to weigh medical evidence. 
 
 Diagnosticians have noted, however, that "zebra"-type diagnoses must nonetheless be held in mind until the evidence conclusively rules them out: 
 
 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. — A. McGehee Harvey, James Bordley II, Jeremiah Barondess[5] 
 
 The term for an obscure and rare diagnosis in medicine is fascinoma. 
 
 Examples [ edit ] 
 
 Necrotic skin lesions in the United States are often diagnosed as loxoscelism (recluse spider bites), even in areas where Loxosceles species are rare or not present. This is a matter of concern because such misdiagnoses can delay correct diagnosis and treatment.[6] 
 
 Counter usage [ edit ] 
 
 Ehlers–Danlos syndrome and hypermobility syndrome are both medical zebras and yet are commonly under diagnosed and misdiagnosed. The EDS and hypermobility syndrome awareness movements have adopted the zebra as the mascot for their campaigning.[7] 
 
 In popular culture [ edit ] 
 
 The television series Scrubs episode "My Balancing Act", focuses on this theme, and the medical veteran Dr. Cox uses the metaphor to explain to intern John "J. D." Dorian why he should first consider a simple diagnosis. 
 
 The television series House had the working title Chasing Zebras, Circling the Drain,[8] a reference to the show's recurring theme of hunting for obscure diagnoses while a patient is in a critical condition. The title character, diagnostic expert Dr. Gregory House rejects the aphorism, arguing that any cases with simple solutions would have been successfully diagnosed by someone else before reaching him. 
 
 The episode "Zebras" of the television series Law & Order: Special Victims Unit was named after this term and cites a version of the aphorism in the teaser. 
 
 Harvard Medical School and Harvard School of Dental Medicine's 2017 music video "IT'S NOT A ZEBRA!" depicts a group of first-year medical students erroneously trying to diagnose a patient with a rare and unlikely disease, when in fact she has the flu.[9] 
 
 Other medical aphorisms [ edit ] 
 
 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's obvious or it's not there [10] 
 
 Hickam's dictum – "Patients can have as many diseases as they damn well please" 
 
 References [ edit ] 
 
 Bibliography [ edit ] ||||| An animal handler from Universoul Circus walks with a zebra, Sunday Nov. 15, 2015, on Righters Ferry Road in Lower Merion, Pa., after two zebras escaped from the Universoul Circus in West Philadelphia. 
 
 Authorities safely corralled two zebras that escaped from a circus in West Philadelphia on Sunday afternoon. 
 
 The zebras "briefly went on the loose" from the UniverSoul Circus outside the Mann Center for the Performing Arts at 52nd Street and Parkside Avenue about 2 p.m., a circus spokesman said in a statement. The animals had just finished performing their act and were in the back lot of the site when they reportedly broke away. 
 
 One zebra was captured within 30 minutes; the second by 3 p.m., according to the spokesman, who was unable to say exactly where the animals were found. No injuries were reported. 
 
 Circus officials were investigating how the zebras were able to escape. 
 
 Before their capture, startled Philadelphians took to social media to post photos and video footage of the zebras running through the streets, with officers hot on their tails. Note: Some videos may contain strong language. 
 
 Just saw a zebra running down city ave... Never a dull moment in philly — Gina Oliveri (@GinBean13) November 15, 2015 
 
 Look here's a little video of them running �� pic.twitter.com/woLShf5lZV — .... (@JahMari_Couture) November 15, 2015 
 
 Zebra headed down City line avenue past the LA Fitness and St. Joes----Is it heading to the Bayou or heading to AI's TGI Friday's? — Justin (@jdjigga4885) November 15, 2015 
 
 Can't find a decent party at st joes but you could find a zebra on city ave pic.twitter.com/eIEsyY8FZR — Alyssa Cuccurullo (@lyscuccurullo) November 15, 2015 
 
 Zebra on the run pic.twitter.com/NwhDCCX8Ge — Matt Reg (@Mattman0007) November 15, 2015
– When you hear hoofbeats, the saying goes, you should think horses, not zebras. In Philadelphia on Sunday, you would have been wrong. A pair of zebras escaped from a circus and went running through the streets of west Philly before they were recaptured, police say. The two animals somehow fled the UniverSoul Circus outside the Mann Center for the Performing Arts at about 2pm Sunday. A circus spokesman told the Philadelphia Inquirer in a statement that the animals "briefly went on the loose." No injuries were reported. Witnesses took to social media to post photos and video footage of the animals running through the streets before police confirmed their recapture at about 3pm Sunday. "Zebras in custody," police tweeted. "They are already sporting old-timey prisoner getup ahead of trial and sentencing. Have faith, fellas." (Three elephants did a lot more damage after escaping from a circus in St. Louis.)