Microscopic colitis (MC) is an inflammatory condition affecting the colon, a part of the large intestine. It is characterized by chronic, watery diarrhea and abdominal discomfort. This condition has two main types: collagenous colitis and lymphocytic colitis. Both types present with similar symptoms, but their diagnosis relies on microscopic examination of colon tissue biopsies. Unlike other inflammatory bowel diseases, the colon typically appears normal during a standard colonoscopy, necessitating a biopsy for a definitive diagnosis.
Medication-Induced Triggers
Certain medications are recognized as significant triggers for microscopic colitis, contributing to inflammation of the colon lining. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and naproxen, are commonly implicated. These medications can potentially irritate the colon or disrupt its normal function, leading to the development of MC.
Proton pump inhibitors (PPIs), widely used to reduce stomach acid, have also been associated with an increased risk of microscopic colitis. Similarly, selective serotonin reuptake inhibitors (SSRIs), which are antidepressants like sertraline, show a link to the condition. While the precise mechanisms are not fully understood, potential factors include direct toxicity to the colon lining, changes in gut permeability, or immune responses. Other drugs briefly linked to MC include ranitidine, acarbose, ticlopidine, and statins.
Immune System Dysregulation
Microscopic colitis is an immune-mediated condition where the immune system mistakenly targets healthy colon cells. This dysregulation leads to chronic inflammation. There is a strong association between MC and other autoimmune diseases.
Individuals with conditions like celiac disease, thyroid disorders (Hashimoto’s and Graves’ disease), rheumatoid arthritis, and psoriasis often develop MC. For instance, up to 60% of patients with lymphocytic colitis and 40% of those with collagenous colitis may have an autoimmune disease. This suggests a predisposition to certain immune responses contributes to colon inflammation.
Infectious and Environmental Influences
External factors can also contribute to microscopic colitis. Certain bacterial or viral gut infections, such as Clostridium difficile or norovirus, can precede or trigger the condition. These infections can initiate an inflammatory response that persists.
Smoking is another significant environmental factor linked to MC. Chemicals in cigarette smoke can damage the gut lining and promote inflammation. Studies indicate that current smokers have a higher risk of developing MC, and this risk increases with greater smoking exposure, though it tends to lessen after quitting. Some research suggests a role for certain dietary components, like artificial sweeteners, though evidence is not conclusive.
Genetic Susceptibility
While not inherited straightforwardly, a genetic predisposition can increase susceptibility to microscopic colitis when exposed to other triggers. A family history of MC or other autoimmune diseases can elevate the risk. Inherited traits can make some individuals more vulnerable to medications, infections, or immune system imbalances.
Research identifies specific genes or genetic markers influencing this susceptibility. For example, variants in the human leukocyte antigen (HLA) 8.1 haplotype associate with an increased risk for collagenous colitis. Genetics help explain why some individuals develop MC while others exposed to similar triggers do not.