Microscopic colitis (MC) is a type of inflammatory bowel condition that causes chronic watery diarrhea. Unlike Crohn’s disease or Ulcerative Colitis, the inflammation in MC is subtle and can only be detected by examining tissue samples under a microscope. Research suggests its development results from a combination of factors, including genetic susceptibility, certain medications, and an overactive immune response.
Defining Microscopic Colitis and Its Subtypes
Microscopic colitis is defined by the need for histological, or microscopic, examination of the colon tissue to confirm the diagnosis. During a standard colonoscopy, the lining of the colon often appears normal, which is why biopsies are essential to identify the underlying inflammation.
The condition is classified into two distinct subtypes based on the specific changes seen in the colon wall. Lymphocytic Colitis (LC) is characterized by a significant increase in lymphocytes within the surface layer of the colon lining. Collagenous Colitis (CC) is defined by a distinct thickening of the collagen layer just beneath the cells lining the colon, often measuring more than 10 micrometers thick. Both subtypes share the common symptom of chronic watery diarrhea and many of the same risk factors.
Primary Etiological Theories
The underlying cause of microscopic colitis is multifactorial, involving a complex interplay between the body’s internal systems and external factors. One strong theory centers on immune system dysregulation, where the body mistakenly attacks the colon lining. This autoimmune-like response leads to the chronic inflammation that characterizes MC.
Genetic predisposition also plays a role in determining susceptibility. While specific genes are still being studied, the condition is often seen in individuals who possess certain genetic markers, suggesting an inherited vulnerability. This genetic background may lower the threshold required for environmental triggers to initiate the inflammatory cascade.
Another important area of focus is the role of luminal factors and the gut microbiota. An imbalance in this gut flora, known as dysbiosis, contributes to the disease by altering the intestinal barrier’s function and triggering an inflammatory reaction. Antigens or toxins produced by altered gut bacteria may seep through a compromised gut lining, initiating the immune response.
Proven Medication Triggers
Several classes of commonly used medications have been implicated in inducing or exacerbating microscopic colitis. These agents trigger the condition by disrupting the colon’s protective mechanisms. Discontinuation of the suspected drug often leads to symptom improvement, highlighting their direct role in the disease process.
Nonsteroidal Anti-inflammatory Drugs (NSAIDs), such as ibuprofen and naproxen, are among the most common culprits. These drugs damage the colon lining by inhibiting prostaglandin synthesis, which is necessary for maintaining the integrity of the mucosal barrier. The resulting damage can allow irritants to penetrate the deeper layers of tissue and trigger inflammation.
Proton Pump Inhibitors (PPIs), including omeprazole and esomeprazole, are also frequently associated with MC, particularly with long-term use. These medications reduce stomach acid, which can lead to changes in the composition of the gut microbiota (acid suppression-related dysbiosis). This alteration in the gut environment promotes the inflammatory state characteristic of MC.
Selective Serotonin Reuptake Inhibitors (SSRIs) have been implicated as well. The exact mechanism is not fully clear, but it may involve the drug’s effect on gut motility or its potential to directly affect the mucosal lining. The risk appears to increase with continuous exposure.
Associated Conditions and Risk Factors
Certain demographic factors and co-existing medical conditions are frequently observed alongside microscopic colitis. The condition is most commonly diagnosed in older adults, typically those over 50, with the mean age of presentation often around 60 to 65 years. Women are disproportionately affected, being up to seven times more likely to develop the condition than men.
Microscopic colitis shows a strong association with other autoimmune disorders. Individuals with MC frequently have co-existing conditions such as Celiac disease, Thyroid diseases, and Rheumatoid Arthritis. This clustering of autoimmune conditions provides further support for the theory that MC is driven by a generalized, dysregulated immune response.
Bile Acid Malabsorption (BAM) is another factor often found in patients with MC. This condition involves an impaired ability to absorb bile acids in the small intestine, causing an excess to enter the colon. These unabsorbed bile acids irritate the colon lining, contributing to the watery diarrhea and inflammation seen in MC.