Microscopic colitis is a general term for two related conditions: lymphocytic colitis and collagenous colitis. Like Crohn’s disease and ulcerative colitis, it is an inflammatory bowel disease.
Microscopic colitis is characterized by inflammation of the mucosal lining of the large intestine (colitis). While inflammation of the intestines is usually visible in a colonoscopy as redness or other signs of inflammation, this is not the case with microscopic colitis. Instead, the pathological abnormalities of microscopic colitis can only be detected by observing tissue samples (biopsies) under the microscope, which explains the term “microscopic” colitis. Because this condition is accompanied by chronic inflammation of the intestines, it is classified as an inflammatory bowel disease (IBD) together with Crohn’s disease and ulcerative colitis.
Microscopic colitis can be divided into two different forms: collagenous colitis and lymphocytic colitis. Both conditions were discovered relatively recently: collagenous colitis was first described in 1976 and lymphocytic colitis in 1980. Although these two conditions are both classified under the general term of microscopic colitis, tissue samples taken from the large intestine reveal different microscopic presentations (histological appearances) for each. Specifically, collagenous colitis is characterized by thickened connective tissue (the collagen layer) in the intestinal mucosa. With lymphocytic colitis, an increased number of a certain type of white blood cells called lymphocytes is found. If it is not possible to classify the histological appearance to either of these two forms, the condition is called incomplete microscopic colitis.
The exact cause of microscopic colitis remains unknown. It is suspected that the disease may be triggered by an interplay of genetic and environmental factors. It is conceivable that bacterial or viral infections as well as certain medications may play a role. Smoking is known to be a risk factor for developing microscopic colitis.
In Europe, about 5-17 out of every 100,000 people develop microscopic colitis each year (incidence), although this rate varies greatly by region. While no specific figures are available on the incidence of microscopic colitis in Germany, there are estimated to be more than 10,000 new cases each year.
The actual figures are probably even higher, since microscopic colitis is often misdiagnosed as irritable bowel syndrome due to the similarity in symptoms and the normal appearance of the bowel during a colonoscopy (tissue samples are required for the diagnosis of the disease, but are not always taken). Therefore, it must be assumed that there are a substantial number of unreported cases.
Many more women than men suffer from microscopic colitis. It is not known why there is such a gender imbalance. The disease frequently starts around the age of 50 to 60 years.
The most important symptom of microscopic colitis is chronic, watery diarrhea that is often accompanied by upper abdominal pain, nausea, flatulence, fatigue, and some degree of weight loss. Many patients also experience diarrhea at night. Blood or mucus in stool are rare.
The disease can severely impact patients’ quality of life due to the symptoms described here.
Patients with microscopic colitis frequently suffer from accompanying diseases. Important examples include conditions that do not affect the gut, such as rheumatic conditions (like arthritis), psoriasis, thyroid dysfunction, gluten intolerance (celiac disease), and vascular disorders.
The symptoms of microscopic colitis may resemble those of irritable bowel syndrome. It is therefore important not to rush to a diagnosis, even when no major abnormalities are observed by colonoscopy. Instead, a careful and cautious process of diagnosis is crucial for effective treatment.
The process of collecting a patient’s complete medical history includes asking the patient about his or her prior medical history as well as current symptoms, how long they last, and how severe they are.
The doctor will also ask the patient whether he or she has any known food allergies or other allergies and whether any of the patient’s relatives might also suffer from IBD or microscopic colitis.
In most cases, collection of medical history is followed by a comprehensive physical examination, during which the doctor will palpate (gently touch) the abdomen or perform an ultrasound examination. Laboratory tests will also be performed.
The most important test for microscopic colitis is a colonoscopy. However, unlike other inflammatory bowel diseases, microscopic colitis cannot be confirmed just by colonoscopy of the large intestine, since it usually appears normal. Instead, multiple tissue samples from the intestinal mucosa must be taken at specific intervals and then examined under a microscope.
In patients with collagenous colitis, a thickened collagen layer is visible under the microscope when the pathologist examines the tissue samples using special dyes. Collagen fibers are a specific type of protein structure that performs a supportive function in the body. While the collagen layer of the intestinal mucosa is less than 5 micrometers (millionths of a meter) thick in healthy people, it is at least 10 micrometers thick in people with collagenous colitis.
In contrast, the most obvious feature of lymphocytic colitis under the microscope is the accumulation of a certain type of white blood cell. The number of these cells is about four to five times higher in people with lymphocytic colitis than in healthy people.
Targeted medications are available to treat microscopic colitis. The goal of this treatment is to alleviate the symptoms of the disease, or even to eliminate them entirely, so that patients experience a better quality of life for a long time.
Very positive outcomes are common with budesonide, an active ingredient that belongs to the group of corticosteroids (sometimes simply called steroids). Budesonide in formulations designed for the treatment of gastroenterological diseases only becomes released and active in the large intestine themselves, where it has anti-inflammatory effects. It is then broken down in the liver. These features give the agent a high degree of effectiveness while keeping the side effects lower than conventional systemic (meaning active in the entire body) corticosteroids. The drug can be taken in several different oral forms which deliver the active ingredient specifically to the intestines. Budesonide is currently the only agent that is approved for the treatment of microscopic colitis.
According to studies, treatment with budesonide at a dosage of 9 mg daily leads to a major reduction in stool frequency after about 2 weeks, in many cases with no more diarrhea at all (remission), in about 80% of patients.
However, the disease and the symptoms return within a few months for most patients if they stop taking the drug once their original symptoms go away. If this happens, guidelines recommend repeating induction therapy at 9 mg budesonide to achieve remission again, then lowering the dose to 3 to 6 mg daily.
With microscopic colitis, is not necessary to switch to a special diet. However, it is important to eat a varied and balanced diet as is typically recommended by nutrition experts. Tests should also be performed to determine whether a microscopic colitis patient might also have gluten intolerance (celiac disease), since people with one of these conditions often have the other one as well.
Smoking is known to have a negative impact on the course of the disease. Therefore, smokers who are diagnosed with microscopic colitis should quit.
Outlook and prognosis
Because microscopic colitis is not a life-threatening disease, it usually has a benign outcome. However, if left untreated, about half of all patients will experience chronic or recurring diarrhea, which can massively impact their quality of life.
Microscopic colitis does not increase the risk of developing colorectal cancer according to the current scientific knowledge.