Can IBS ever be misdiagnosed?

Coeliac UK have had some success today in promoting this survey in the world press, and well done, I say. Coeliac disease is a disease that affects sufferers' lives in many unpleasant ways, not least by raising their risk of malignacies in the gut. It is relatively easy to screen for with tests that are increasingly sensitive and specific. Once diagnosed, it is easy to control, albeit with significant dietary restriction. Coeliac UK are doing a great job, and I applaud them for it. So, then. Why do you feel a rant approaching?

The problem I have is with the phrase "incorrectly diagnosed with irritable bowel syndrome"; the phrase is illogical, but those of you expecting a spirited defence of doctors in cases of medical error are to be disappointed. When irritable bowel syndrome is diagnosed, it is always a misdiagnosis, not because it doesn't cause genuine suffering, not because doctors always get it wrong, but because the condition, IBS, is not a diagnosis at all.

What is a diagnosis? Etymologically it doesn't take much to guess it's a Greek term, dia  meaning "apart" and gnosis meaning "recognition". It is a way we label or pidgeon-hole diseases to make them easier to understand, and to create a foundation from which we form a management plan. Often this is useful. No two heart attacks will ever be identical, but if one doctor says, "Acute Myocardial Infarction" to another doctor, the process of a plaque of cholesterol in the wall of a coronary artery cracking, leading to blood clot formation inside the artery which subsequently blocks a downstream branch of that artery and leads to death of a portion of the heart muscle is understood by both. Both also understand that the principles and to a large extent the details of management of such a condition is the same (at least in the initial stages). It is a recognised disease process, with recognised principles of treatment, and "acute myocaridal infarction" is adequate shorthand for this. It is a diagnosis. The same is true of Crohn's Disease, pyogenic granuloma, indirect inguinal hernia, primary syphilis, acute bacterial conjunctivits and, yes, Coeliac disease. So why not IBS?

If we examine the process by which a diagnosis is made, it relies on knowledge of the diasease processes of all possible diagnoses at any given point in the process - this is known as the differential diagnosis, or merely the "differential". My next patient already has a differential diagnosis, and I don't even know who that patent is yet. The differential is written in the index of all the medical textbooks on my shelf (except, obviously, one of the ones under "I"). When I see that patient's name I start refining that differential. If they are called Peter, I can discard the gynaecology textbook. If Peter is 76 I can also discard the paediatric one. Gradually, through parallel processes of asking questions, examining him and performing investigations, I refine the differential diagnosis until I have only a few items on the list. The last refinement usually comes with a trial of treatment, and a review if things don't go according to expectations. At any point I can decide what to do next only by considering the differential, and, with knowledge of the disease processes of all the items on that differential, working out what is the most discriminating step. So, again, why not IBS?

Well, IBS doesn't represent a single disease process. It is not even an umbrella term for a group of disease processes that are pathologically similar. The symptoms might be similar, but that by no means correlates with the disease processes being similar. A better known example is diabetes. There are three distinct diseases named diabetes because they make you wee a lot - diabetes is the Greek (again) for "fountain". They appeared similar to the Greeks, so got the same name. But they are very different at a biochemical level. So what is IBS?

Well the diagnostic pathway usually goes something like this:

- patient presents with bowel symptoms of some sort.
- doctor asks questions that might point to serious bowel disease, such as rectal bleeding, appetite or weight loss. All are answered negatively.
- doctor runs some blood tests (which definitely should include a tissue tranglutaminase and/or anti-endomysial antibody or their equivalents to test for Coeliac disease) and they come back normal.
- doctor begins to struggle and handles this by referring to a speicalist.
- specialists repeat the tests already done in case the bottles were labelled incorrectly.
- specialist inserts a long, thin, black camera into one or several orifices and finds no pathological process ongoing.
- patient is told they "probably have IBS". They are given some leaflets, and sent away to bloat unhappily.

This defines IBS; it is not a disease, but the cul-de-sac of medical knowledge about the gut. The known diseases have been exhausted. You have unpleasant symptoms which medicine cannot explain. But... but... we can't quite bring ourselves to say, "I don't know". We're not the sorts who like not to know. We are clever, see? And actually, if you're honest, you don't want us not to know either. You want certainty, because "if we don't know what it is, we don't know what it isn't, right?" So what do we do. We collude. We both tap our noses and say, "Ah, it's IBS". And if we're really cheeky, "That's what I thought all along".

You then ask what IBS is. We will evade that question by pointing you in the direction of a website, or a support group. We might offer you a leaflet. We may prescribe you a high fibre diet. We may prescribe you a low fibre diet. If you're constipated, we'll give you laxatives. If you've got diarrhoea, we'll give you Imodium. We will be sympathetic. We'll try different treatments if the first ones don't work. Just please, please, please, don't try and ask what IBS actually is. That will break the magic. We won't know, and if you don't accept the flannel straight away, you might get another one of those cameras inserted. You have been warned.

Beacuse IBS is a non-diagnosis. It defines your condition by what it isn't, not what it is. There are probably thousands of yet-to-be-discovered pathological processes which we currently call IBS. None of them are dangerous. None of them are curable, either, at least for the time being. Wouldn't it be better if we all stopped pretending that we know what we're talking about? What if we abandonded the term as a diagnosis, or, even better, altogether? That would be honest. That would be good.

Well I say good, but it may not feel it. You would have to trust a doctor who had admitted not knowing everything. You would have to accept the possibility that there are some conditions currently in the IBS umbrella which are mild, otherwise undetectable versions of real bowel diseases, which if we only wait will become diagnosable later. Yes, we might need to do that camera thing a second (or if you pushed it earlier, a third) time. Why would you want to do that?

Well it's because the process isn't perfect. Misdiagnoses do happen, becasue doctors' knowledge can never be perfect, because there isn't time to examine you fully every time we see you and becase disease hasn't read the textbook. If you are an IBS sufferer it means we don't know what is causing your symptoms. (By the way, that doesn't mean we think you're making them up either). You are in a holding stack, and when you are given that diagnosis, you are set up to manage your symptoms as and when they happen, but constantly to question new or changing symptoms to see if your condition can be taken off the holding stack and landed properly on a specific runway. For sure some people are destined never to land, to stay in the holding stack for ever. But some have undiagnosed Coeliac disease. Or Crohn's disease, or malignancy. And the problem with seeing IBS as a runway, not a stack - a diagnosis rather than a non-diagnosis - you stop looking for the real runway.