Microscopic colitis is often misdiagnosed as irritable bowel syndrome. Microscopic colitis is the collective term applied to two inflammatory conditions of the colon, collagenous colitis and lymphocytic colitis.
Unlike irritable bowel syndrome, which is a functional disorder of the colon, microscopic colitis is an inflammatory bowel disease. Both conditions share similar symptoms which can lead to a misdiagnosis.
Sudden onset of diarrhea is a symptom of microscopic colitis. Stools are watery and not bloody. Typically, a person with either collagenous colitis or lymphocytic colitis can have 4 to 9 daily bowel movements. As many as 20 daily bowel movements are possible. The symptom of diarrhea becomes constant. However, some individuals may experience periods of improvement followed by worsening. Other symptoms include abdominal cramping, bloating, some weight loss, and fecal incontinence. The symptoms of irritable bowel syndrome include abdominal pain, diarrhea or constipation or a combination of both.
Microscopic colitis is diagnosed by microscopic examination of a biopsy or sample of colon tissue obtained during a colonoscopy. The inflammation is not visible during a colonoscopy. The disease can affect the entire lining of the colon or present in patches on the colon lining. Collagenous colitis is identified by layers of collagen, which is a connective protein, in the lining of the colon. It is more common in women than in men. Generally diagnosed in individuals age 50 and older, adults under 45 years old and children, ages 5 to 12 years old have been diagnosed with collagenous colitis. Lynphocytic colitis is identified by the presence of increased lymphocytes, which are white blood cells active in the response of the immune system, among the cells lining the colon. Both men and women are equally affected and typically diagnosed during the 5th decade of life.
The exact cause of microscopic colitis is not known. There are several theories. One thought is that bacteria or a virus initiated the inflammation response. Another possibility is a malfunction in the autoimmune system of an affected person.