A phrase that every medical student has heard during their training is, “When you hear hoofbeats, don’t expect to see a zebra”.  This basically mean you should try to focus on the “obvious”, and not chase rare diseases if the “obvious” makes sense. In medicine, there can sometimes be a tendency to chase and diagnose rare pathology because it’s “sexy”.  We are trained against this because we can cause harm by over-testing and if your final diagnosis makes sense, and fits the overall clinical picture — then you shouldn’t go looking for a zebra.

But when you can’t find a diagnosis that fits the overall clinical picture — it can be difficult to find the zebra.  Often you have to rely on case reports on PubMed or use Google Scholar.  Finding articles using these two methods can be arduous and take a significant amount of time.

Enter Radu Dragusin and colleagues from the Technical University of Denmark, who have created the aptly titled Search Engine — “FindZebra”.  Dragusin and colleagues have indexed specially selected sets of curated databases on rare diseases, such as Orphanet, Online Mendelian Inheritance in Man (OMIM), and even sections of Wikipedia.

Below is their table 1 explaining the resources used to compile the dataset of rare diseases.



Using an open source information retrieval tool, they search this index and the result is FindZebra.com.

I used the FindZebra to look for a zebra diagnosis that was one of my favorites of Residency — Hemophagocytic lymphohistiocytosis (HLH).  Significantly elevated ferritin levels are one of the hallmarks of this rare disease, and when I typed in “high Ferritin”, I did not get HLH in the top 20 diagnoses. But when I added anemia and neutropenia (associated findings), HLH was one of the top 20 diagnoses.

This search engine is exciting.  Obviously, there is still a lot of work that needs to go into Find Zebra as it just launched, but the researchers who created this search engine should be applauded.

FindZebra.com is a novel idea and I certainly think it can be used by Physicians if they are having difficulty with a patient’s diagnosis.  The diagnoses listed by FindZebra can help Physicians expand their differentials and could help shorten the time a rare disease goes undiagnosed.


PDF of research article on FindZebra

Source: Technology Review