Abdominal pain, bloating, and unpredictable bowel habits can feel isolating, especially when symptoms persist despite treatment. Many people receive a diagnosis of irritable bowel syndrome (IBS) based on symptom patterns alone, but several other conditions can produce remarkably similar presentations. Understanding what else might be contributing to gut symptoms is an important step in ensuring the right approach to care.
What is IBS?
Irritable bowel syndrome is a functional gastrointestinal disorder characterised by recurrent abdominal pain and altered bowel habits, typically diarrhoea, constipation, or both. It is diagnosed using clinical criteria when no structural or biochemical abnormalities are found on routine testing. IBS affects around 10 to 15 per cent of adults, and symptoms can significantly affect quality of life.
Because IBS is a diagnosis of exclusion, other conditions must be ruled out before it can be confirmed. Symptom overlap is substantial, and relying on symptoms alone can lead to missed diagnoses.
Why Accurate Diagnosis Matters
Mistaking another condition for IBS can delay appropriate treatment and allow underlying inflammation, malabsorption, or structural problems to progress. Some conditions that mimic IBS carry risks of long-term complications if left unrecognised, whilst others may respond to specific therapies not used in IBS management.
The challenge lies in distinguishing true red flags from benign functional symptoms, and knowing when further testing is warranted.
Conditions That Can Mimic IBS
Inflammatory Bowel Disease
Crohn’s disease and ulcerative colitis can present with cramping, diarrhoea, and bloating, especially in mild or early disease. Unlike IBS, inflammatory bowel disease (IBD) involves chronic inflammation of the gut lining that can lead to ulceration, strictures, and systemic complications.
Red flags suggesting IBD include unexplained weight loss, persistent nocturnal diarrhoea, blood in the stool, raised inflammatory markers such as C-reactive protein or faecal calprotectin, and a family history of IBD. Colonoscopy with biopsy and imaging studies are typically required for diagnosis.
Coeliac Disease
Coeliac disease is an autoimmune condition triggered by gluten, a protein found in wheat, barley, and rye. It causes inflammation and damage to the small intestine lining, leading to malabsorption. Symptoms include bloating, diarrhoea, abdominal pain, fatigue, and anaemia.
Many people with coeliac disease are initially misdiagnosed with IBS, particularly if symptoms improve partially with dietary changes. Blood tests for tissue transglutaminase antibodies and duodenal biopsy during endoscopy are necessary for diagnosis. Gluten must not be removed from the diet before testing, as this can lead to false-negative results.
Small Intestinal Bacterial Overgrowth
Small intestinal bacterial overgrowth (SIBO) occurs when bacteria that normally reside in the colon migrate into the small intestine and multiply excessively. These bacteria ferment carbohydrates, producing gas and contributing to bloating, distension, diarrhoea, and discomfort.
SIBO is more common in people with conditions that slow gut motility, such as diabetes, scleroderma, or previous abdominal surgery. It can also occur following gastric acid suppression with proton pump inhibitors. Breath testing for hydrogen and methane after ingestion of a sugar substrate is the most commonly used diagnostic tool.
Bile Acid Diarrhoea
Bile acid diarrhoea, also known as bile acid malabsorption, occurs when bile acids produced by the liver are not properly reabsorbed in the terminal ileum. They enter the colon, where they stimulate water secretion and cause diarrhoea. Symptoms include watery stools, urgency, and cramping, often mistaken for diarrhoea-predominant IBS.
This condition is more common after ileal resection or in Crohn’s disease affecting the terminal ileum, but can occur without obvious cause. A therapeutic trial of bile acid sequestrants such as colestyramine or colesevelam, or a SeHCAT scan where available, can help confirm diagnosis.
Microscopic Colitis
Microscopic colitis refers to two related conditions, collagenous colitis and lymphocytic colitis, that cause chronic watery diarrhoea. The colon appears normal during colonoscopy, but biopsies reveal characteristic inflammation.
Microscopic colitis is more common in older adults and has been linked to certain medications, including proton pump inhibitors and nonsteroidal anti-inflammatory drugs. It can also occur alongside autoimmune conditions. Diagnosis requires colonoscopy with multiple biopsies from across the colon.
Lactose Intolerance
Lactose intolerance occurs when the enzyme lactase, which breaks down lactose in dairy products, is deficient. Undigested lactose is fermented by gut bacteria, leading to bloating, gas, abdominal pain, and diarrhoea shortly after consuming dairy.
Primary lactase deficiency is common worldwide and often develops in adulthood. Secondary lactase deficiency can follow gut infections or inflammation. A trial of lactose elimination followed by reintroduction, or breath testing, can clarify whether lactose is contributing to symptoms.
Gynaecological Conditions
Endometriosis, ovarian cysts, and pelvic inflammatory disease can all cause cyclic or chronic abdominal and pelvic pain that may be mistaken for IBS, particularly in women. Pain linked to the menstrual cycle, painful periods, or pain during intercourse should prompt consideration of gynaecological causes.
Endometriosis can involve the bowel and cause symptoms such as diarrhoea, constipation, or rectal bleeding during menstruation. Pelvic ultrasound, magnetic resonance imaging, or laparoscopy may be required for diagnosis.
When to Seek Further Investigation
Certain symptoms warrant further assessment and should not be attributed to IBS without investigation. These include onset of symptoms after age 50, unintentional weight loss, nocturnal diarrhoea, rectal bleeding, anaemia, a family history of bowel cancer or IBD, and persistent symptoms despite treatment.
Raised inflammatory markers on blood tests or elevated faecal calprotectin also suggest underlying inflammation rather than functional disease. A thorough clinical assessment, including detailed history and examination, helps guide appropriate testing.
Practical Takeaways
- Keep a symptom diary that includes timing, food intake, and bowel movements to help identify patterns.
- Report red flag symptoms such as blood in the stool, weight loss, or night-time symptoms to your GP or gastroenterologist.
- Do not eliminate gluten or lactose from your diet before testing if coeliac disease or lactose intolerance is being considered.
- Ask about the tests that have been performed and whether further investigation might be appropriate.
- Remember that IBS is a real condition, but ruling out other causes ensures you receive the right care.
Conclusion
Symptom overlap between IBS and other gastrointestinal conditions is common, and distinguishing one from another requires careful assessment. While IBS is a valid and manageable diagnosis, it should not be assumed without appropriate investigation, particularly when red flag features are present. Identifying the correct underlying cause ensures that treatment is targeted, effective, and safe over the long term.
References
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This article is intended for informational and educational purposes only. It does not constitute medical advice and should not be used as a substitute for professional medical guidance, diagnosis, or treatment.