Erythema Nodosum

Erythema nodosum is a type of inflammatory condition that affects the skin. Its name translates to “red knots” and it often presents with raised, tender and often painful lumps that form under the skin. These lumps most often appear on the front of the leg or shin, but can appear anywhere on the body.

Erythema nodosum (EN) is a result of inflammation in the fatty layer of the skin, and can accompany inflammatory conditions like inflammatory bowel disease (IBD). Generally, symptoms of EN coincide with a flare-up of Crohn's or ulcerative colitis, however, they can come at any time. EN bumps go away over time and often subside when a flare-up ends without leaving behind any long-term symptoms or scars. In addition to the red lumps, EN can cause systemic (or whole-body) symptoms including fever, chills, and joint pain.1-4

What causes erythema nodosum?

For those who do not have a previous diagnosis of IBD, EN is often considered idiopathic, meaning it has no known root cause. Some known causes of EN include other inflammatory conditions, such as sarcoidosis (an inflammatory condition that affects the lungs, skin, and other organs) or an infection, such as strep throat.

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Other less common infectious causes of EN include herpes simplex virus, hepatitis B and C viruses, HIV, bacterial infections, and parasitic infections. EN can also be developed as a reaction to certain medications, including oral contraceptives (birth control pills) or antibiotics. Occasionally, EN can accompany pregnancy, and very rarely, EN can be caused by cancer, including lymphoma.1,2

How common is erythema nodosum?

Overall, the incidence of EN has been estimated to be one to five cases per every 100,000 people. Specific to IBD, it has been estimated that EN affects anywhere from 2-10% of individuals with Crohn's or UC, and occurs more frequently in women than in men. Individuals between the ages of 20 and 30 years old are most commonly affected by EN, but the reason for these patterns is still unknown.1,3

How are the red bumps evaluated and diagnosed?

The diagnosis of EN can be done in a variety of ways. Identifying and treating EN often involves diagnosing the underlying condition causing it, if there is one. Symptoms of EN generally resolve once treatment for the condition causing them has been started. Sometimes, diagnosis and evaluation may be as simple as a doctor taking past medical history and learning that an individual has, or has recently had, a condition that can cause EN, such as IBD, sarcoidosis or strep throat.

Although the diagnosis may be made by just looking at the lumps, sometimes a biopsy is performed to ensure that no other condition is causing the inflammation and that the lumps are benign. If the cause of EN is not obvious or has not already been diagnosed, a doctor may complete blood tests or x-rays to look for other conditions that may be causing the lumps and may help lead to a diagnosis. Sometimes, the lumps may be confirmed to be EN by visual exam, but no cause is identified.1,4

How is erythema nodosum treated?

The treatment for EN is often the same as the treatment for the underlying condition, such as inflammatory bowel disease (IBD). Therefore, symptoms of EN often disappear once that treatment begins. It may take 2-8 weeks for the bumps to clear, and they do not leave any marks or scars. Common treatments for underlying conditions, like IBD, that can help resolve EN include systemic steroids and immunomodulating mediations (medicines that suppress or change the functioning of the immune system).

In some cases, treatment with potassium iodide may be appropriate. If the cause of EN is unknown, nonsteroidal anti-inflammatory drugs (NSAIDs) and cold compresses may be used to manage pain and swelling. It is important that a physician is made aware of any history of IBD, since treatment with NSAIDs may lead to a flare of IBD symptoms. This shows why it is essential for your doctor or healthcare team to try to determine the underlying cause as best as possible in order to find the most appropriate treatment option.1-4