Reviving Case Reports: Chasing Zebras or Solving Mysteries?

I am teaching a new course this week entitled “Turning your Clinical Cases into Scholarly Work.”  I hope to draw on my own experiences through the years mentoring students and residents in writing up several clinical cases, but also in making diagnoses.  In preparing for this course, I have also learned quite a bit about the controversy surrounding case reports and the challenges that they face in today’s healthcare system. 

Unfortunately, case reports have fallen out of vogue.  Many journals no longer accept case reports or they have relegated them to the 2nd class ‘online’ only publication since they are often not highly cited and lead to a lower journal impact factor.  Critics of case reports actually say they overemphasize the unusual at the expense of the ordinary and are not evidence-based.  Furthermore, in today’s era of cost consciousness medicine, chasing ‘zebras’ or unique diagnosis is often frowned upon due to the potential for inappropriate or overuse of tests, with the possible unintended consequences of working up incidentilomas

Despite these concerns, case reports have had a major impact on the discovery of new diseases, mechanisms of disease and even drug therapies.  The first cases of AIDS were reported as case reports.  Side effects of drugs are often discovered through case reports and can lead to changes clinical practice (MRI contrast and nephrogenic systemic fibrosis) to prevent harm.  Cases reporting potentially desired side effects can also prompt accidental discovery of new drugs that can change quality of life for many people, as is the case with Viagra

So, how can we promote the art of case reports without creating zebra chasers who drive up healthcare costs?  Well, the key may lie in Sherlock Holmes.  Medicine is often compared to detective work and it is well known that Sherlock Holmes used the power of observation to make informed deduction.  While Holmes was a fictional character, the invention of Sir Arthur Conan Doyle (a doctor turned writer), he was modeled after Dr. Joseph Bell, Doyle’s former physician-mentor.  To get his trainees interested in observation, Dr. Bell used the power of observation to deduce mundane things like occupation and recent activity in passersby.  In essence, the clues to making the diagnosis lie in careful understanding of the patient’s story and observation of the physical cues.    

Unfortunately, the powers of observation are declining these days due to the ease of ordering CT scans without thinking about a patient.  Fear of malpractice also drives the use of diagnostic testing over trusting one’s self.  To make matters worse, diagnostic tests are financially rewarded, while thinking about the right test to order to make the diagnosis is not.  If the art of diagnosis were more handsomely rewarded, more hospitals would actually have a “Department of Diagnostic Medicine” led by their own version of Dr. House (who is based on Holmes incidentally …and Chasing Zebras was considered as a title of the show).  As stated by Rapezzi and colleagues…

Current trend towards mass use of sophisticated diagnostic tools in routine practice—accompanied by a blind faith in technology and predefined diagnostic algorithms—is threatening to kill off the science and art of clinical reasoning. Besides burning a lot of public and private money to make diagnostic work rather superficial, doctors also risk losing the intellectual pleasure that comes from careful diagnostic reasoning.

So, in considering how to revive case reports and the art of diagnosis, its worth revisiting lessons dating back to the old adages that been used to teach generations of doctors before the proliferation of imaging.  While each of these rules has its faults, they represent a return to thinking about the diagnosis.   If only it was only as simple as, “It’s elementary, my dear Watson”…   

Occam’s Razor – “entities must not be multiplied beyond necessity” refers to the thought there is usually one unifying diagnosis.  The term razor is used to highlight shaving away unnecessary assumptions to get to simplest explanation. 

Hickam’s dictum – “Patients can have as many diseases as they well please” The counterfactual to Occam’s razor is credited to John Hickam, MD who highlights that it is statistically more likely for a patient to have several common diseases explaining a constellation of symptoms rather than a rare zebra.  The best example of this is Saint’s triad which consists of gallstones, hiatal hernia, and diverticulosis which don’t have anything to do with each other other than they are often common in patients.

Pasteur’s dictum  – ‘chance favors only the prepared mind’  This refers to the fact that to make the ‘leap’ of discovery, one must have the knowledge & skills to be able to make the connection.  In other words, you cannot find an interesting case if you are not reading and know what to look for.

Sutton’s lawFirst, consider the obvious.  In other words, conduct the test which will confirm (or rule out) the most likely diagnosis.  This phrase is named for bank robber Willie Sutton, who when asked why he robbed banks supposedly answered “because that’s where the money is.”



  1. I Firmly believe that case reports hold an important teaching aspect that cannot be garnered from reading RCTs or using algorithms. I don’t believe that religation of the case report to interesting side note in major journals is a good thing, but perhaps we should focus on the positives that forcing the publications into an electronic medium gives us. That is the ability to data mine the reports more efficiently and perhaps identify those rare but measureable events such ad drug side effects or new diseases. Perhaps in their haste to relegate to second tier, they actually will provide a better opprotunity, we simply need to “re-adjust” our observation to the information supplied. Perhaps the next great medical investigator will wield google analytics and hashtags instead of a twill cap or fist full of vicodin.

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