Crohn's disease after gastroenterologist Burrill Bernard Crohn, who, in 1932, together with two other colleagues at Mount Sinai Hospital in New York, described a series of patients with inflammation of the terminal ileum of the small intestine, the area most commonly affected by the illness. Many people with Crohn's disease have symptoms for years before the diagnosis. The usual onset is between 15 and 30 years of age, but can occur at any age. Because of the 'patchy' nature of the gastrointestinal disease and the depth of tissue involvement, initial symptoms can be more subtle than those of ulcerative colitis. People with
Burrill Bernard Crohn 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. Crohn noted that it can be difficult for physicians to correctly differentiate neuroses from diseases of the organs.