Finally published. Made with Deepseek, Claude, and OpenEvidence. I think it's the most exhaustive list you can find on IBS mimics. Christensen (1994) and Camilleri and Boeckxstaens (2023) served as starting papers, and then I added a few more entities that I remembered. u/Robert_Larsson, if any diagnosis is missing, please let me know. I've been wanting to make this post for quite some time.
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u/ariaxwest
This is awesome! I've also thought about this a lot as I've had at least two diagnoses missed and been diagnosed with IBS. I wasn't diagnosed with celiac disease until I was 30 years old, despite being in constant pain and suffering from reduced nutrient absorption since I was a baby.
Under inflammatory and immunologic entities, you should include food allergies and hypersensitivity to metals and chemical compounds.
My daughter had been diagnosed with IBS-C, but in reality she had casein allergy. Dairy free diet ended her constipation. I don't think we ever would have figured this out if she hadn't had allergy testing.
Starting a few years after going gluten-free due to celiac disease, I again had severe diarrhea over a long period of time. This time I became so ill that I almost died, and again of course was diagnosed with IBS-D. This time it was due to nickel hypersensitivity. I was finally diagnosed by a dermatologist. Nickel hypersensitivity in particular causes so much intestinal inflammation and symptoms identical to IBS. One study I read found previously unknown and undiagnosed nickel hypersensitivity in almost 40% of patients who had been diagnosed with IBS.
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u/jmct16
Missed some (by Grok)
Trehalase deficiency: Malabsorption of trehalose (found in mushrooms and certain insects), causing fermentation and IBS-like symptoms after specific ingestion.
Biomarker: Trehalose hydrogen breath test or genotyping.
Status: Rare but under-recognized; in active separation in centers performing expanded disaccharidase testing.
Dyssynergic Defecation (also called pelvic floor dyssynergia or anismus): Impaired coordination between abdominal push and pelvic floor relaxation during defecation, leading to straining, incomplete evacuation, and symptoms indistinguishable from severe IBS-C.
Biomarkers: High-resolution anorectal manometry + balloon expulsion test (BET); defecography.
Status: Fully separated in guidelines for refractory constipation. Rome IV now allows diagnosis alongside IBS-C. Biofeedback therapy is highly effective (success rates >70%), often curative, and is recommended before labeling patients as having refractory functional constipation or IBS-C. This entity exemplifies how "IBS" can be an artifact of incomplete physiological testing.
Persistent post-viral or post-COVID gastrointestinal symptoms: Low-grade inflammation, dysmotility, or barrier dysfunction following acute viral gastroenteritis (including SARS-CoV-2). Shares biology with classic post-infectious IBS (PI-IBS) but has surged post-pandemic. Status: Nosological debate ongoing (similar to PI-IBS); some propose "reactive gut disorder" or "long gut" as distinct labels. History of infection plus exclusion of other causes is key.
Symptomatic uncomplicated diverticular disease (SDD): Chronic abdominal pain, bloating, and altered bowel habits in the presence of diverticula without overt inflammation. Status: Largely consolidated separation (already noted by Christensen in 1994), yet still frequently mislabeled as IBS in older patients.
Cantu syndrome-related GI dysmotility (mutations in KCNJ8/ABCC9 — KATP channels): Gain of function leads to intestinal contractility dysfunction. Status: rare, but an elegant example of channelopathy beyond SCN5A/GUCY2C; reported in humans and murine models with severe cold.
Dyssynergic defecation (ou pelvic floor dysfunction / anismus): Contradição na coordenação do assoalho pélvico durante evacuação, mimetizando IBS-C grave. Biomarcadores: manometria anorretal + teste de balão de expulsão. Status: fully separated em guidelines (ACG recomenda testes fisiológicos em refratários); biofeedback é tratamento curativo em muitos casos. Prevalência alta em IBS-C refratária.
Eosinophilic activation in IBS-D (without frank eosinophilic gastroenteritis): Increased activated eosinophils in the jejunal/colon mucosa, correlated with severity in IBS-D. They produce CRF and contribute to hypersensitivity. Biomarker: eosinophil count/immunohistochemistry in biopsy + activation markers. Status: in advanced research; not fully isolated, but explains subgroup with low-grade inflammation.
Dyssynergic defecation (or pelvic floor dysfunction/anismus): Contradiction in the coordination of the pelvic floor during defecation, mimicking severe IBS-C. Biomarkers: anorectal manometry + expulsion balloon test. Status: fully separated in guidelines (ACG recommends physiological testing in refractory cases); biofeedback is curative treatment in many cases. High prevalence in refractory IBS-C.
Giardia lamblia (giardiasis) a classic — yet frequently under-appreciated — example of a condition that migrates out of the broad IBS diagnosis, particularly in the context of post-infectious IBS (PI-IBS) and chronic diarrhea workups.
Dientamoeba fragilis: Causes chronic diarrhea, abdominal pain, and IBS-like symptoms; known for propensity to cause prolonged infections. Frequently overlooked because standard labs may not perform the required stained smears. Biomarker/Diagnosis: Microscopy of stained fecal smears or PCR. Status: Emerging recognition as a treatable cause of chronic symptoms misdiagnosed as IBS.
Cryptosporidium spp.: Waterborne parasite causing prolonged diarrhea, especially in outbreaks or immunocompromised patients. Strongly associated with PI-IBS development, with symptoms persisting long after clearance. Biomarker/Diagnosis: Stool antigen or PCR. Status: Well-documented trigger for PI-IBS; separable with specific testing in chronic diarrhea workups.
Cyclospora cayetanensis: Similar to Cryptosporidium; causes watery diarrhea and fatigue, often linked to contaminated produce. Can lead to prolonged or post-infectious symptoms. Biomarker/Diagnosis: Stool microscopy or PCR.
Entamoeba histolytica (non-dysenteric amebic colitis): In endemic areas or travelers, it mimics IBS-D with chronic diarrhea and pain without overt dysentery. Non-invasive forms are particularly hard to distinguish from functional disorders. Biomarker/Diagnosis: Stool antigen/PCR (distinguish from non-pathogenic E. dispar). Status: Classic mimicker; guidelines recommend testing in appropriate risk groups.
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u/VisiblePlatform6704
Another one that may need to be included: A1 Casein intolerance:
A1 casein intolerance is a condition where digestion of the A1 beta-casein protein found in most European dairy cattle releases beta-casomorphin-7 (BCM-7), a peptide that activates opioid receptors in the gastrointestinal tract and causes symptoms mimicking lactose intolerance. Unlike true lactose intolerance, which stems from insufficient lactase enzyme activity, A1 intolerance is linked to the A1 beta-casein variant produced by a mutation that occurred in European cattle roughly 5,000–10,000 years ago, whereas A2 beta-casein (found in Asian/African cattle and some modern breeds) does not release significant amounts of BCM-7
I've got a VERY strong case of this, so much that even eating something like chips that have "milk powder" would provoke swollen intestines, diarrhea and other stuff. Meanwhile, drinking/eating A2 casein milks is completely fine.
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u/Gastronomicus
All of them. That's what IBS is - a collection of GI issues without a diagnosis of disease. Every one of them has a disease behind it, but they're sometimes difficult to detect.
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u/ariaxwest
Another possible missed diagnosis: congenital anatomical differences. Possibilities include intestinal hypermobility, common in people with HEDS, Hirschsprung’s disease, and intestinal malrotation.
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u/Ambitious-Ad-4301
I have to say, I often wonder how easy it would be to miss that you may have colon cancer due to some of the effects of IBS and what is normal for you is also what is sometimes the first signs of cancer.
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u/Robert_Larsson
What I can come up with from memory only:
SLC5A1 Gene causing Glucose-Galactose malabsorption (carb enzyme category)
DGAT1 mutation causing diarrhea
Stem cell proliferation (covered by the original causes above in part)
Cystic Fibrosis (doesn't mask IBS but GI issues and EPI are common and forgotten)
Adrenal Insufficiency (GI issues often forgotten and labelled functional)
We could probably expand this list by going more into detail on some categories like the neuropathies or immune activation, not to speak of the intestinal microenvironment where dysbiosis, parasites and infections can be of so many origins. The problem is that we are diving in from meta to minutia so quickly and frequently, it becomes hard to keep track.
Nice work buddy, we should be doing more of this to keep it moving in future.
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u/magskii
Excellent.
Another one not on the list, from the UK: My mum was initially diagnosed with IBS when what she actually had was a huge gallstone. No one bothered to offer any tests other than basic bloodwork. They only figured it out when she had an ultrasound for a completely different reason. The technician spotted and mentioned it, assuming my mum already knew because it was so obvious!
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u/jmct16
u/BulkySquirrel1492 Finally, a detailed review. It considers mimickers to be rare. There are many entities to be considered beyond a 'positive IBS diagnosis'.
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u/frankwittgenstein
It's a useful summary which goes on to show the political and economic dimensions of diagnosing people with "severe DGBI".
I'd say it's a more difficult task to organize this topic into fully distinct entities than in this table, as there is some inevitable overlap, e.g. some of the congenital diseases here will also be neuropathies (Hirschprung's), some of the metabolic/neurological may also be congenital/hereditary (mitochondrial diseases), and so on. Another thing is that in some cases etiologies are listed alongside diseases/phenotypes, e.g. myenteric plexitis is likely etiology of some cases of enteric neuropathies, like CIPO. Apart from that, the immune system may also be a driver of mitochondrial diseases (Hanaford and Johnson 2022, for instance).
Which brings us to another point, that there will also be some overlap in etiologies within a single disease, i.e. GI symptoms in some autoimmune diseases will likely be a mixture of mitochondriopathies, connective tissue autoimmunity and neuropathy. Within diseases with neuropathy, etiologies can span both large- and small-fibers, or be limited to small-fiber neuropathy of ENS and/or PNS.
You could also add autoimmune/rheumatic diseases into the table (in fact, I have an entire book on gastrointestinal manifestations of rheumatic diseases) — Sjogren's, RA, Enteropathic Arthritis, Ankylosing Spondylitis, Psoriatic Arthritis, SLE, Scleroderma, Myositis, Vasculitis. Again, they will often have a mixed etiology, e.g. in Sjogren's, GI symptoms being the outcome of a mix of xerostomia, small-fiber neuropathy and probably connective tissue autoimmunity, which will also inevitably vary between patients. On a more microscopic scale, mitochondria will likely be affected too. IBS diagnosis probably won't mask them, but some clinicians like to refer to GI symptoms of people already diagnosed with those rheumtic diseases as IBS, FD and so on, which is obviously incorrect (this opens another discussion on where to draw the line between "comorbidity" and the actual symptom in a subset of patients diagnosed with the disease).
There is also more recently described Yao Syndrome, which actually has similar genetic mutations to Crohn's (NOD2 gene).
On a side note, I'd be cautious with overly relying on commercial LLMs used for similar tasks, as they are subject to capitalist logic as everything else (the same logic, that within the medical framework gave us DGBI in order to save healthcare spending per capita) — their main purpose is to appeal to investors. They are often correct (I find them useful on occasion too, mostly for preliminary looking for a query that will be too specific for standard search engines), but they will bridge the gaps in data with making conjectures, as what attracts investors is a technology that sounds smart and confident, even when data on the topic is pretty limited. They may also share biases of the research they are aggregating.