I have been doing quite a bit of research about Crohn's since my son was diagnosed. I found, quite by accident, during my own investigation that there is a not very highly publicised condition which has the same symptoms as Crohn's - stomach distress, diarrhea, et al.
It's called "Celiac Disease" and is an intolerance (allergy? or autoimmune response?) to the protein in wheat called 'gluten', and a few other grains. Gluten is naturally occuring in wheat. However, it's also the protein that makes bread dough stretchy and so these days it is added to commercial bread products in addition to what's already in the wheat flour.
Researchers are just beginning to associate Celiac with Crohns and I wouldn't be surprised if they found out the intestinal damage caused by Celiac (due to addl amts of gluten put into modern bread) in fact lead to Crohns. --My own postulation.
Ayway, the two diseases present with the same symptoms as I stated above. But, Celiac can be controlled by adhering to a life-long gluten free diet alone.
Much better to ask your doctor for the simple test for Celiac than be misdiagnosed or underdiagnosed (as in having both), and the possiblility for multitudes of toxic drugs that Crohn's requires if it's Celiac in addition/instead.
It is possible to have both as my son does. A gluten-free diet has much improved his condition though. If more people are diagnosed with both (as I suspect) there will be more research and possible changes.