by Jason Wasserman MD PhD FRCPC
March 29, 2026
Chronic active colitis is a pattern of inflammation in the colon that a pathologist describes after examining tissue under a microscope. The word chronic means the inflammation has been present for a long time, months to years. The word active means it is currently causing ongoing injury to the colon lining. Together, they paint a picture of a colon that has been repeatedly damaged and has not fully recovered.
Chronic active colitis is not a diagnosis in itself — it is a description of what the tissue looks like. Your doctor will use this information, along with your symptoms, colonoscopy findings, and other test results, to determine what is causing the inflammation. The most common cause is inflammatory bowel disease (IBD), but other conditions can produce the same pattern. If this finding is in your report and you are unsure what it means for you specifically, that is a completely reasonable place to be — this article will help explain what the pathology report is describing and what questions to ask your care team.
What are the symptoms?
Inflammation damages the inner lining of the colon and prevents it from working normally. The most common symptom is diarrhea, which occurs because the damaged lining can no longer absorb water effectively. Other common symptoms include abdominal pain or cramping, bloating, blood or mucus in the stool, and unintended weight loss.
Symptoms may flare up and then improve, or they may be persistent. Their severity often reflects the extent and activity of the inflammation.
What causes chronic active colitis?
The most common cause is inflammatory bowel disease (IBD), a group of conditions in which the immune system mistakenly attacks the colon. The two main types are ulcerative colitis and Crohn’s disease. These two conditions share many microscopic features, and pathologists often cannot distinguish between them from a biopsy alone. Your doctor will factor in your symptoms, the pattern seen during colonoscopy, and the distribution of inflammation across the colon before making a final diagnosis.
Other conditions that can produce a similar pattern of chronic active colitis include:
- Infections. Certain bacterial, viral, or parasitic infections can cause chronic colitis, particularly in immunocompromised individuals or those who have recently travelled.
- Medications. Some drugs — including certain antibiotics, anti-inflammatory medications, and immune checkpoint inhibitors used in cancer treatment — can trigger chronic inflammation in the colon.
- Ischemic colitis. Reduced blood flow to part of the colon can cause ongoing damage that, under the microscope, resembles IBD.
- Diversion colitis. Inflammation can develop in a segment of the colon that has been surgically bypassed and is no longer carrying stool.
In some cases, a clear underlying cause is not immediately identified, and further testing or follow-up is needed.
How is the diagnosis made?
Your doctor will perform a colonoscopy — a procedure that uses a small flexible camera to examine the inside of the colon. During the procedure, multiple small tissue samples, called biopsies, are taken from several locations along the colon. Taking biopsies from multiple sites is important because inflammation in IBD and other conditions can affect different parts of the colon in different ways. A single biopsy from one area may not capture the full picture.
The tissue is then sent to the pathology laboratory, where a pathologist examines it under a microscope and looks for the features described below.
What does the pathology report describe?
The report describes two types of changes: features of chronicity (evidence of long-standing damage) and features of activity (evidence of ongoing, current injury). Both are usually present in chronic active colitis.
Features of chronicity
These changes develop over time due to repeated or sustained inflammation. They tell the pathologist that the colon has been inflamed for months or years, not just days or weeks.
- Crypt distortion. The inner surface of the colon is lined by tiny tube-shaped structures called crypts. Normally, they are straight, evenly spaced, and parallel. Long-term inflammation causes them to become irregular in shape, abnormally branched, shortened, or reduced in number. Pathologists call this crypt architectural distortion, and it is one of the most reliable signs of chronic IBD.
- Basal lymphoplasmacytosis. This term refers to a buildup of immune cells — specifically lymphocytes and plasma cells — at the base of the mucosa, the inner lining of the colon. These cells are not normally found in this location in a healthy colon. Their presence is a strong indicator of chronic inflammation.
- Paneth cell metaplasia. Paneth cells are specialized cells normally found in the small intestine and the right side of the colon. When they appear in parts of the colon where they do not belong — such as the left colon or rectum — it is a sign the tissue has been repeatedly damaged and has changed its cell composition over time. This change is called metaplasia.
- Granulomas. A granuloma is a compact cluster of immune cells, primarily histiocytes, that forms in response to persistent inflammation. Granulomas in the colon are strongly associated with Crohn’s disease and are not typically seen in ulcerative colitis. Finding granulomas in a biopsy is one of the features that helps pathologists and clinicians lean toward a diagnosis of Crohn’s disease.
Features of activity
These changes reflect inflammation occurring right now — the “active” part of chronic active colitis. They are produced mainly by neutrophils, a type of immune cell that responds to acute injury.
- Cryptitis. Neutrophils have moved into the crypt wall itself. This is one of the earliest signs of active inflammation and indicates that the colon is actively being damaged. It can also suggest that current treatment is not adequately controlling the disease.
- Crypt abscesses. A collection of neutrophils has accumulated inside the central space of a crypt. Like cryptitis, this is a sign of active disease and often indicates either early-stage IBD or inadequate disease control.
- Ulceration. The inner lining of the colon has been destroyed in one or more areas, leaving a raw, open surface. Ulceration is a sign of severe active inflammation. It can occur in both Crohn’s disease and ulcerative colitis and often indicates that the inflammation is not well controlled.
How severe is the inflammation?
Pathologists often describe the overall severity of active inflammation as mild, moderate, or severe based on the number of neutrophils and the extent of damage observed.
- Mild activity. Small numbers of neutrophils are present in or around the crypts. The lining of the colon is damaged but largely intact.
- Moderate activity. More widespread cryptitis or crypt abscesses are present. The damage is more significant.
- Severe activity. Extensive neutrophil infiltration, widespread crypt destruction, or ulceration is present. This indicates that the inflammation is causing substantial, ongoing injury to the colon.
The severity described in the pathology report gives your gastroenterologist important information about how well the current treatment is working and whether a change in therapy may be needed.
What happens next?
Chronic active colitis requires ongoing management by a gastroenterologist — a doctor who specializes in digestive diseases. The next steps depend on the underlying cause and the severity of the inflammation.
If IBD is suspected or confirmed, treatment typically involves medications to reduce inflammation and suppress the immune response. Common options include aminosalicylates (such as mesalazine), corticosteroids for flares, immunosuppressants, and biologic therapies. The goal of treatment is to achieve and maintain remission — a state in which inflammation is controlled and the lining of the colon can heal.
Follow-up colonoscopies are usually recommended to assess how well the colon is healing in response to treatment. People with long-standing IBD — particularly ulcerative colitis involving the entire colon — are also monitored for dysplasia, since chronic inflammation over many years can increase the risk of colorectal cancer.
If an infection or medication is the cause rather than IBD, the treatment is different: addressing the infection directly or stopping the offending medication often resolves the inflammation.
Questions to ask your doctor
- What do you think is causing the chronic active colitis in my case?
- Does the pattern suggest ulcerative colitis, Crohn’s disease, or something else?
- How severe is the active inflammation, and what does that mean for my treatment?
- Is my current treatment controlling the inflammation effectively, or does it need adjustment?
- When should I have a follow-up colonoscopy?
- What symptoms should prompt me to contact you before my next scheduled visit?
- Do I need to be monitored for colorectal cancer, and if so, how often?
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