Microscopic colitis is a chronic inflammatory condition affecting the large intestine, or colon. It is a recognized cause of persistent diarrhea that can significantly impact daily life. This article explores how common microscopic colitis is and identifies the groups of people most frequently affected.
What Microscopic Colitis Is
Microscopic colitis is an inflammatory disease of the colon that causes frequent, watery diarrhea. Unlike other inflammatory bowel diseases like Crohn’s or ulcerative colitis, the colon lining usually appears normal during a standard colonoscopy. The inflammation is only visible when tissue samples are examined under a microscope.
There are two primary subtypes: collagenous colitis and lymphocytic colitis. Collagenous colitis is distinguished by a thickened layer of collagen beneath the colon’s surface lining. Lymphocytic colitis involves an increased number of lymphocytes within the colon tissue. Both subtypes share similar symptoms and are often treated similarly.
How Common Is It?
Microscopic colitis is now recognized as a common cause of chronic diarrhea, with its incidence and prevalence increasing over recent decades. A meta-analysis indicated a worldwide incidence of approximately 4.9 cases per 100,000 person-years for collagenous colitis and 5.0 cases per 100,000 person-years for lymphocytic colitis. Overall prevalence for microscopic colitis has been reported around 103.0 per 100,000 persons.
The commonality of microscopic colitis has shown a notable upward trend. A Danish nationwide study observed a tenfold increase in incidence from 2.3 cases per 100,000 person-years in 2001 to 24.3 cases per 100,000 person-years by 2016. This rise has led to microscopic colitis surpassing the incidence rates of Crohn’s disease and ulcerative colitis in some countries. While incidence rates have generally increased, some studies suggest a stabilization in recent years.
Geographical variations in commonality also exist. Highest incidences are traditionally noted in North America and Northern European countries. Within the United States, it has been found to be more common in some Southwest states like Colorado, New Mexico, Arizona, and Nevada, as well as other Southern states like Florida, Georgia, and California, contrasting with patterns for other inflammatory bowel diseases.
Why Diagnosing Microscopic Colitis Can Be Challenging
Diagnosing microscopic colitis presents challenges because the colon typically appears normal during visual endoscopic examination. A standard colonoscopy alone is often insufficient; a tissue sample, or biopsy, taken during the colonoscopy, is essential to confirm the condition.
If biopsies are not routinely taken when a colonoscopy appears normal, cases can be missed. Furthermore, symptoms like chronic watery diarrhea and abdominal pain frequently overlap with other gastrointestinal conditions, such as Irritable Bowel Syndrome (IBS). This often leads to initial misdiagnosis, with many patients first diagnosed with IBS.
Increasing awareness among healthcare professionals has contributed to more diagnoses. However, challenges persist, including potential misinterpretation of symptoms and a lack of consistent biopsy guidelines. These diagnostic practices directly influence the reported commonality of the disease, as improved detection naturally leads to a higher number of identified cases.
Populations Most Affected
Microscopic colitis predominantly affects certain demographic groups, with age and gender being significant factors. The condition is most commonly diagnosed in middle-aged to older adults, typically individuals over the age of 50. The median age at diagnosis often falls within the fifth and sixth decades of life, around 60 to 65 years.
Women are more frequently affected than men, showing a clear female predominance. For collagenous colitis, the female-to-male ratio can range from 4.4 to 7.9 to one, while for lymphocytic colitis, it ranges from 1.8 to 5.0 to one. This higher incidence in women may be linked to hormonal factors.
Certain medications have been associated with an increased risk of developing microscopic colitis. These include proton pump inhibitors (PPIs), nonsteroidal anti-inflammatory drugs (NSAIDs), and selective serotonin reuptake inhibitors (SSRIs). Concomitant use of NSAIDs and PPIs has shown a particularly high risk.
Additionally, there is a strong association between microscopic colitis and other autoimmune conditions, such as celiac disease, thyroid disease, rheumatoid arthritis, and type 1 diabetes. Smoking is also recognized as a risk factor, especially in younger adults.