The DDx app was conceptualized by my frequent thought: “I think this looks like “X”. In cases where experts also had “X” high on their DDx list, what were some of the final diagnoses observed/discussed? I liken this to a “reverse DDx” question, where we are looking for all cases where a given Dx was on the DDx. This app facilitates that search. Reading these cases helped me better understand how to think about cases similar to my patients case.