Metastatic Crohn’s disease occurs when inflammation from Crohn’s affects skin areas that aren’t along your digestive tract. In children, these symptoms often appear before typical Crohn’s symptoms.

Crohn’s disease is an inflammatory bowel disease (IBD) that mostly affects your small intestine and the beginning of your large intestine.

But in some cases, inflammation from Crohn’s can manifest in parts of your body unrelated to your gastrointestinal (GI) tract, like your skin. Doctors refer to this as metastatic Crohn’s disease (MCD).

MCD differs from other skin conditions associated with Crohn’s disease, such as pyoderma gangrenosum or erythema nodosum.

First defined in 1965, researchers are still working to understand MCD, its causes, and how best to manage it. Keep reading to learn more about MCD, including its common symptoms and treatment options.

According to the Crohn’s & Colitis Foundation, about 1 in 5 people with IBD experience skin complications.

Most Crohn’s skin lesions occur as an extension of GI inflammation. Ulcers and rashes may appear on areas of skin along the GI tract, such as your mouth, perineum, or anus.

With MCD, however, some of these skin lesions develop away from the digestive tract inflammation. This means you might experience skin problems in areas not next to your GI tract.

Lesions associated with MCD most often develop in the following areas:

  • genitals
  • legs
  • arms
  • abdomen
  • skin folds

Less commonly, MCD may develop on your face, breasts, or trunk. Additionally, you may have multiple MCD lesions or up to a few consolidated in one area.

Skin lesions or plaques from MCD may be:

  • red, purple, or brown, depending on your skin tone
  • ulcerated
  • inflamed and tender to the touch

A doctor may diagnose MCD if you have Crohn’s disease and some of its common skin effects. They will confirm their findings with a skin exam and a biopsy.

In some cases, doctors may diagnose MCD before you have a Crohn’s disease diagnosis.

To confirm the presence of Crohn’s disease, a doctor may:

  • ask you about possible GI symptoms, such as chronic diarrhea, abdominal pain, or unintentional weight loss
  • look for physical signs, such as abdominal bloating and liver or spleen enlargement
  • run certain blood tests
  • perform an intestinal endoscopy
  • order a CT scan
  • order an upper GI series

Your doctor may also need to rule out other skin conditions that look like MCD. These include:

There’s no consensus on how best to treat MCD because it’s so rare.

Treatment varies. Ultimately, it depends on the severity and location of skin lesions.

A doctor may first prescribe topical corticosteroids or calcineurin inhibitors, which you apply directly to the affected areas of skin.

If topical therapies don’t work, a doctor may recommend oral steroids, biologics, or immunosuppressants. These medications may also help in cases where MCD affects multiple areas of the body.

Some cases, such as those that involve the perineum, may require surgery. The perineum is the area between your genitals and anus.

It’s not clear what exactly causes MCD.

Some researchers have theorized that immune system overactivity may contribute to inflammation along vessel walls or through the circulatory system before affecting the skin. Researchers are also investigating possible genetic factors.

While this skin complication develops in people with Crohn’s disease, experts consider it rare compared with other types of Crohn’s skin symptoms.

Not everyone with Crohn’s disease will develop MCD. Furthermore, it’s possible to develop MCD a few months or several years before Crohn’s, especially for children.

Experts estimate that at least half a million U.S. adults have Crohn’s disease. It typically develops when you’re in your 20s.

Some studies have found that almost half of people with Crohn’s experience related skin conditions. The two most common of these conditions are erythema nodosum and pyoderma gangrenosum.

But MCD is rare, with fewer than 100 reported cases in the medical literature since 1965.

Groups with a higher risk of MCD include females, younger adults, and children.

There’s currently no cure for MCD. The effects of treatment are highly individual.

Since MCD is so difficult to treat, cases are often recurring and persistent. Reported cases of spontaneous resolutions also exist, but research in this area is lacking.

MCD is a rare condition in which Crohn’s disease inflammation causes skin symptoms beyond the path of the digestive tract. Some people develop MCD before they receive a Crohn’s diagnosis.

If you or a loved one develops unexplained lesions or plaques, with or without Crohn’s, it’s important to talk with a doctor as soon as possible. An accurate diagnosis is key to getting the treatment you need to reduce your symptoms and improve your quality of life.