Indeterminate Colitis Overview

The most common forms of inflammatory bowel disease (IBD) are ulcerative colitis and Crohn's disease. But there is a third diagnosis—indeterminate colitis. The term indeterminate colitis is used when a person has features of IBD, but it's not yet understood which form of the disease it is.

This is a confusing and controversial topic in IBD, with broad implications for treatment. It's estimated that anywhere between 10% and 15% of people with IBD are thought to have indeterminate colitis. In some situations, a diagnosis of another form of IBD might be made later on, as the disease changes.

What Indeterminate Colitis Is

IBD is often positioned as being an umbrella term under which Crohn's disease and ulcerative colitis fall. Major differences between the two main forms of IBD are that ulcerative colitis causes superficial ulcers in the colon, while Crohn's disease causes patchy inflammation throughout the digestive tract, often with deep ulceration.

There are some situations where a person has a type of IBD that can't be classified into either one of those buckets.

This doesn't mean that a diagnosis of Crohn's disease or ulcerative colitis won't be made in the future. It just means that the ongoing features of the disease don't make the diagnosis clear.

The distinction can be unclear at any disease stage:

• Colitis that has advanced beyond its initial stages may be difficult to classify because of the nature of the inflammation and how extensive it can be in the colon.
• It can be difficult to make a solid diagnosis when the disease is in remission because the disease features are minimal or are not present.
• Early disease is sometimes difficult to diagnose because the cellular changes of IBD that could be seen with a biopsy may not be present yet.

Signs and Symptoms of Indeterminate Colitis

Rather than being a mash-up of various characteristics of both ulcerative colitis and Crohn's disease, indeterminate colitis is associated with a set of signs that was originally described in 1978—although they are not hard and fast rules.

Indeterminate colitis could have all or some of the attributes below:

Type of Ulcers

Indeterminate colitis might be used in cases where the inflammation is only in the large intestine, but the ulcers don't look like those typically caused by ulcerative colitis.

In ulcerative colitis, the ulcers found in the large intestine will only involve the most superficial layer of the mucosa, which lines the intestinal wall. If those ulcers are deeper than what would normally be expected with ulcerative colitis, and there's no other indication that the disease is actually Crohn's disease, it might lead to a preliminary diagnosis of indeterminate colitis.

These ulcers are sometimes described as transmural (meaning they go deep through the intestinal wall) or as being like fissures. In some cases, the fissure-like ulcers are narrow (about 13% of cases); sometimes they are shaped like a V (about 60% of cases).

Rectal Involvement

Another characteristic of indeterminate colitis is that the rectum is often not involved, or at least not fully involved.

In ulcerative colitis, the rectum tends to be inflamed in most cases. In Crohn's disease, the rectum may or may not show inflammation.

Skip Lesions

In Crohn's disease, inflammation may skip areas of the intestine, leaving a patchwork of inflamed areas between areas of healthy tissue. In ulcerative colitis, the inflammation begins in the rectum and continues up through the colon in a continuous pattern.

With indeterminate colitis, there may be areas that appear to be skipped over (i.e., free of inflammation). There could be several reasons this can happen, which is why this attribute can be another factor that doesn't always help in making a solid diagnosis.

Diagnosis

The definition of indeterminate colitis doesn't currently have standardization, although there are some broad guidelines. However, with indeterminate colitis, the characteristics can be different between patients. In fact, IBD is a complicated disease that is difficult to classify.

There are some cases of indeterminate colitis that are thought of as "probable Crohn's disease" while others are "probable ulcerative colitis," which means there are patients in the indeterminate classification who could be anywhere on the entire spectrum between these two diseases.

Change in Diagnosis

In most cases, a diagnosis of either Crohn's disease or ulcerative colitis is eventually reached. When and why this happens is highly variable.

In some cases, if new inflammation crops up in the small intestine when there previously was only inflammation in the colon, a diagnosis of Crohn's disease can be made.

Certain complications, either intestinal or extra-intestinal, are more common with one form of IBD over the other, and their presence can help in making a diagnosis.

Being diagnosed with one of the forms of IBD is important because it helps shape an effective treatment plan. While many treatments are approved by the Food and Drug Administration (FDA) for both forms of IBD, others are only approved for either Crohn's disease or ulcerative colitis. What's more, certain treatments might also be somewhat more effective for one of these diseases than the other.

Treatment

In most cases, indeterminate colitis is treated with the same medications and surgeries as ulcerative colitis. If there is inflammation in the small intestine (such as the first part, which is the ileum); in that case, the approach might be similar to the treatment of Crohn's disease.

The treatment plan for indeterminate colitis might include these medications:

• Asacol (mesalamine)
• Azulfidine (sulfasalazine)
• Immunosuppressants: Imuran (azathioprine), Purixan (6-MP, mercaptopurine), Neoral (cyclosporine)
• Rheumatrex (methotrexate)
• Biologic medications: Remicade (infliximab), Humira (adalimumab), Entyvio (vedolizumab), Simponi (golimumab), and Stelara (ustekinumab)
• Small molecules: Xeljanz (tofacitinib), Zeposia (ozanimod), and Rinvoq (upadacitinib)
• Corticosteroids: Entocort EC (budesonide) and prednisone

Surgical procedures for indeterminate colitis are also similar to that of ulcerative colitis and include ileal pouch-anal anastomosis or IPAA (more commonly called a J-pouch) and ileostomy.

J-Pouch Surgery

Some people with indeterminate colitis undergo J-pouch surgery, which is typically reserved for use only in people who have an established diagnosis of ulcerative colitis.

During J-pouch surgery, the large intestine is surgically removed and the last part of the small intestine is made into a pouch the shape of a "J" and attached to the anus (or the rectum, if any is left by the surgeon). The J-pouch takes the role of the rectum and holds stool.

Studies have shown that people with indeterminate colitis tend to do slightly less well with J-pouches than people who have ulcerative colitis. However, other researchers have pointed out that the failure rate of a J-pouch in patients with indeterminate colitis could be high because the disease characteristics are not uniform—that is, there's too much variability to study this group of patients as a whole.

This surgery is not typically done for Crohn's disease because there's a small risk that the pouch may later become affected by Crohn's and need to be removed.

Ileostomy

During an ileostomy, the colon is removed and the end of the small intestine is brought through an incision in the abdomen (which is called a stoma).

A person with an ileostomy wears an appliance on the abdomen to catch stool, which leaves the body through the section of the small intestine that's outside of the body.

Stool collects in the appliance and is emptied into the toilet as needed.

A Word From Verywell

Some people may have a diagnosis of indeterminate colitis for a while before being diagnosed with ulcerative colitis or Crohn's disease. This can come with a fair amount of uncertainty, making disease management challenging.

Finding a healthcare team that is fully supportive, assembling and leaning on a network of family and friends that can offer assistance and understanding, and learning as much as possible about IBD can help you learn to manage your symptoms and recognize new or changing features of your condition that need medical attention.