Check this article about early ileal ulcers

1. Mild symptoms AND abnormalities in the terminal ileum when they first got the mild bowel symptoms.Not ALL patients with mild symptoms and totally normal biopsies.

In the present study, lesions that on follow-up proved to be idiopathic and clinically insignificant were morphologically similar to lesions that eventually proved to be early Crohn disease and to those caused by NSAIDs. It was not possible to distinguish the subset of lesions that were early Crohn disease. Most of the patients with isolated nonspecific ileal erosion in this study (57%) had idiopathic and clinically insignificant lesions.[24] This result is similar to those of earlier studies that collectively report that in 44% to 48% of patients with isolated ileal disease, typical Crohn disease eventually develops

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So if you had lesions in the ileum when you were first evaluated or you start seeing blood in the stool or other symptoms of autoimmune disease go back and get re-evaluated.What I think they were looking for were markers of early crohn's so the high percentage of patients in this study was because they picked out the people that had a something on the initial colonoscopy (and you get the same little bit of something if you take NSAIDS and stopping that makes it go away) and did a follow up on them.That should be much less scary than they looked at all people the vast majority who had nothing abnormal in the biopsies and almost all of them ended up in a bad place. Considering most people with IBS have mild symptoms for decades and it is never anything else that should help calm you down a bit.Looks like in finding early crohns if you have symptoms and a small something on the biopsies you need more follow up for the first few years after that happens to catch things IF they happen when they start up.At minimum get your annual physical and make sure they do a complete blood count because if your sedimentation rate goes up that means you probably should get your insides looked at again.I mean a LOT of diseases start off pretty mild and while there are some minor abnormalities they are also in the range of people who never go on to have any future problems. Not everything starts with a bang. Most start off fairly mild. This is why I always say if your symptoms change, or get worse than your usual go back and get checked out again and not pretend everything that ever happens after an IBS diagnosis must just be IBS. Sometimes people have other things and it takes awhile for it to really get going or you get something else after a few years.One problem is if you continually examine every symptom every time all the time to try to freak yourself out that this particular pain (which was pretty low in these patients) or stool shape or color or volume is the one that proves you really are going to be seriously ill you will make your IBS a lot worse than it has to be.Medical students go through this when they get into the which diseases cause which symptom part of their education. It is really common for them to find something insignificant they can blow up into a full blown panic that they have something really gruesome. However there isn't any more disease in medical students than any other group of 20 somethings. Anyone that starts trolling the medical literature is likely to get a bit of medicalschoolitis because eventually you will find something you can use to scare the bejeezus out of you. If you are prone to that sort of anxiety I would avoid looking for trouble.

IBD is an autoimmune disease. The usual suspects for triggers is a usual immune response to something you should have a response to, but for some people a part of what is used to identify what is you vs what is not you is a bit too close to the whatever you were fighting off legitimately. People who have certain genes in that "self vs not self" system are more prone to autoimmune problems than others.The problem is something cross-reacts to the self and then you start attacking that part as if it were foreign. So most of the treatments aim at reducing that inappropriate immune system response.IBS is a functional disease. From studies of people who have a GI infection and looking at them 1 year out compared to other people who didn't have a GI infection during that year you find the people who have a GI infection have a much greater chance of having IBS. Inflammation in the colon like what you would see from fighting off a GI infection has been shown to damage the nervous system of the gut and they find some problems in the nervous system of the gut in people with IBS and generally the drugs that treat it best tend to work on the nervous system (both drugs approved for IBS work on specific serotonin receptors in the gut). You do find some functional problems in people with IBD (so when all signs of inflammation in the blood and in the colon/small intestine are back to appearing normal they have IBS symptoms) and it is thought that the nerves can be damaged from that immune response just as they can be from an appropriate immune response to something like Salmonella.