Diarrhea is unfortunately an all-too-common digestive symptom that can be disruptive in daily life and even dangerous for certain vulnerable people. Most people experience acute cases from time to time that resolve on their own. Chronic diarrhea, on the other hand, often persists for weeks or months and typically stems from an underlying condition rather than being caused by something eaten recently. Most of the time that means a gastrointestinal condition like IBD, but another possibility that often gets overlooked is microscopic colitis.

What Causes Acute and Chronic Diarrhea?

Acute diarrhea is the term for the familiar temporary form of diarrhea that most people have experienced. It can happen to anyone of any age, though it generally doesn’t pose a significant threat to the person’s long-term health. Acute diarrhea can be triggered by a wide range of stimuli that have a similar effect on the digestive tract. Conditions like stomach viruses, antibiotic treatments, and meals that don’t sit right are all examples of factors that can temporarily disrupt the normal rhythm of the digestive tract.

During the normal process of digestion, the colon absorbs water from the waste material passing through. Yet if something causes the lining of the digestive tract to become irritated or inflamed, bowel motility increases and pushes contents through faster than the colon can process them. The result is the loose, watery stools that are characteristic of diarrhea. Fortunately, in most cases the trigger itself is temporary and normal function returns in a matter of days.

In cases of chronic diarrhea, when symptoms persist for four weeks or longer, this typically means that something is actively and repeatedly interfering with normal bowel function in ways that won’t self-correct. What this means is that chronic diarrhea rarely resolves without identifying and treating the underlying condition that drives it. Common gastroenterological conditions like inflammatory bowel syndrome (IBS) often end up being the culprit, but microscopic colitis is a more elusive possible cause that requires a deeper look.1

What Is Microscopic Colitis?

One of the reasons microscopic colitis can be difficult to diagnose is that it doesn’t behave like the inflammatory bowel conditions patients may already be familiar with. Conditions like Crohn’s disease and ulcerative colitis often produce visible signs of inflammation that can be identified during a colonoscopy. Microscopic colitis, by contrast, causes persistent symptoms even when the lining of the colon appears completely normal during the same exam.

This apparent contradiction is where the condition gets its name. The inflammation is only visible when tissue samples collected during a colonoscopy are examined under a microscope. Without those biopsies, there may be little evidence that inflammation is present at all, and patients can experience chronic watery diarrhea for months or even years before the underlying cause is identified.

Despite the lack of visible inflammation, the cellular changes in microscopic colitis are enough to disrupt how the colon functions on a day-to-day basis. Rather than the temporary irritation that drives most acute cases of diarrhea, microscopic colitis involves sustained inflammatory activity in the tissue lining itself. In one form, collagenous colitis, a thickened band of collagen develops beneath the surface of the colon wall and physically impedes its ability to absorb fluid. In the other, lymphocytic colitis, an excess of white blood cells accumulates in the lining and interferes with normal function. The symptoms and treatment are similar for both, but in either case the result is the same persistent, watery diarrhea that won't resolve on its own.

Risk Factors for Microscopic Colitis

The inflammation behind microscopic colitis doesn’t appear to have a single identifiable trigger in most cases, but certain patterns show up consistently enough to guide both diagnosis and prevention. The condition is most commonly diagnosed in adults over the age of 50 and occurs significantly more often in women than in men. It also appears more frequently in patients who already have an autoimmune condition such as celiac disease, rheumatoid arthritis, or thyroid disease, which suggests that the same kind of immune dysfunction involved in those conditions may also contribute to chronic inflammation in the colon.

Certain commonly prescribed medications have been linked to an increased risk as well. Proton pump inhibitors (PPIs) used to treat acid reflux, nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen, and selective serotonin reuptake inhibitors (SSRIs) used to treat depression and anxiety have all shown associations with the condition. Not everyone who takes these medications will develop microscopic colitis, and in many cases no single cause can be identified. But when a patient presents with chronic watery diarrhea, a medication review is often one of the first steps in the diagnostic process.

Treatment Options for Microscopic Colitis

Because there is no single cause of microscopic colitis, treatment typically begins by identifying and addressing whatever may be contributing to the inflammation. The specific approach depends on symptom severity, the patient’s overall health, and whether any medications or underlying conditions appear to be involved. Common treatment strategies include:

  • Medication review: If a medication like a PPI, NSAID, or SSRI is suspected of contributing to symptoms, a physician may recommend adjusting the dose or switching to an alternative. This decision is always made under medical supervision, since many of the medications associated with microscopic colitis serve important therapeutic purposes elsewhere.
  • Dietary adjustments: While no single diet has been shown to be effective for all patients with microscopic colitis, many find that limiting known irritants like caffeine, alcohol, artificial sweeteners, and high-fat foods helps reduce the frequency and severity of diarrhea during active flares.
  • Anti-diarrheal medications: For mild cases, over-the-counter medications like loperamide can help slow bowel activity and reduce stool frequency. These don’t address the underlying inflammation but can improve daily quality of life while other treatments take effect.
  • Anti-inflammatory therapy: Budesonide, a locally acting corticosteroid, is widely considered the first-line treatment for microscopic colitis. It targets inflammation directly in the colon while producing fewer systemic side effects than traditional steroids, and it is effective at inducing remission in a large majority of patients. Because symptoms frequently return after a course of budesonide ends, some patients benefit from a low-dose maintenance regimen to keep the condition in check over the longer term.
  • Additional therapies for persistent cases: A small percentage of patients do not respond adequately to budesonide or experience frequent relapses despite maintenance therapy. For these cases, a gastroenterologist may recommend advanced treatments that target the immune system more broadly, including biologic therapies that have shown strong results in recent clinical use.

Contact Cary Gastro for Diarrhea Relief

Chronic watery diarrhea that persists for weeks without a clear explanation deserves a thorough evaluation. Microscopic colitis is one of the conditions our specialists at Cary Gastro look for during that process, and diagnosing it starts with knowing to take the right biopsies during a colonoscopy. If you or someone you know is dealing with ongoing digestive symptoms, contact Cary Gastro to request an appointment.


1https://fg.bmj.com/content/11/3/228
2https://www.mdpi.com/2077-0383/12/13/4442