Crohn's work with his own patients as well as research on 1,500 similar cases helped correct the thinking that the ailment was actually a form of tuberculosis rather than an inflammatory disease of the gastrointestinal tract.

Some of Crohn's initial research into the causes of the Crohn's disease was centered around his personal conviction[citation needed] that it was caused by the same pathogen, a bacterium called Mycobacterium paratuberculosis (MAP), responsible for the similar condition that afflicts cattle called Johne's disease.

However, he was unable to isolate the pathogen—most likely because M. paratuberculosis sheds its cellular wall in humans and takes the form of a spheroplast, making it virtually undetectable under an optical microscope.

This theory has resurfaced in recent years and has been lent more credence with the arrival of more sophisticated methods of identifying MAP bacteria.

[7] For most of his long career, Crohn had a private practice in New York City and was associated chiefly with Mount Sinai Hospital.

[8] He received numerous awards and professional honors, wrote extensively for doctors and the general public, and was asked to consult on high-profile patients from all over the U.S. and abroad.

[10] In addition to practicing medicine, Crohn enjoyed painting and studying the history of the American Civil War.

[1] Crohn practiced medicine until he was 90, splitting time in his later years between the Upper East Side of Manhattan and a country home in New Milford, Connecticut.