What is erythema nodosum?
Erythema nodosum is a type of inflammation in the layer of fat right underneath your skin. This results in tender or painful lumps that may feel warm. These lumps usually appear on your shins, but they may also appear on your forearms, thighs, or across your chest, stomach, and back.
It's usually caused by a reaction to an infection, such as strep throat or COVID-19, or a medication, such as penicillin or sulfa drugs. Sometimes it's caused by an erythema nodosum associated medical condition, like inflammatory bowel disease (IBD) or Behcet's disease.
Erythema nodosum itself isn't serious and it usually goes away on its own in 1-6 weeks.
Erythema Nodosum Symptoms
The tender lumps, also called nodules, of erythema nodosum usually form on both your shins. Sometimes, though, the nodules may appear anywhere on your arms, chest, stomach, butt, back, or legs. On light skin tones, the nodules may look red or purple.
On dark skin tones, they may look dusky purple, gray, or black, or your skin could take on a different texture. For instance, your skin may peel or you may get pimple-like bumps.
The nodules can be as big around as a penny or a lime. They may be tender and swollen off and on for a few weeks. They can take 1-2 months to heal all the way, and they may look like bruises as they fade to your natural skin tone. They usually don't leave scars, but sometimes you may get a little pit in your skin where your fat layer has been injured.
Symptoms of erythema nodosum include:
- Lumps under your skin that may be warm and tender and look like a bruise
- Low-grade fever
- Feeling sick (malaise)
- Swollen lymph nodes
- Joint pain, especially in your ankles and knees
- Weight loss
- Stomach pain, vomiting, or diarrhea
Rarely, you may have another form called chronic erythema nodosum. In this form, the lumps may join to make large, raised patches on your skin, but these patches tend to be less tender than the nodules.
Erythema Nodosum Causes
Erythema nodosum can happen as a reaction to an infection or medication or because of an underlying medical condition.
Infections that can cause it include:
- Strep throat
- Viral upper respiratory infections, such as a cold or COVID-19
- Hepatitis B and C
- Valley fever (coccidioidomycosis), a disease caused by a fungus that grows in the soil and dirt in some parts of the Southwestern U.S., parts of Mexico, and Central and South America
- Histoplasmosis, a lung infection caused by a fungus that grows in soil that has lots of bird or bat droppings. This is mostly in the Central and Eastern states of the U.S., Central and South America, Africa, Asia, and Australia
- Some sexually transmitted diseases, such as chlamydia, gonorrhea, or chancroid
- Bacterial gastroenteritis
Medications that can cause it include:
- Antibiotics, such as penicillin, amoxicillin, and ciprofloxacin
- Sulfa drugs, sulfamethoxazole and trimethoprim (Bactrim or Septra)
- Birth control pills
Underlying medical conditions or erythema nodosum-associated conditions include:
- Inflammatory bowel disease (IBD), such as ulcerative colitis or Crohn's disease
- Rheumatic fever
- Behcet's disease, a rare condition that causes swelling in the blood vessels throughout your body
- Sweet syndrome
- Some cancers, such as leukemias and lymphomas
In many cases, doctors may not be able to tell what caused you to get erythema nodosum.
Erythema Nodosum Diagnosis
Your doctor may also order tests, including:
Blood tests and culture tests to help find any infections. Blood tests may include a complete blood count (CBC) with differential, an erythrocyte sedimentation rate (ESR), and a level for C-reactive protein. Some doctors may order culture tests, such as a throat culture to look for strep throat or a stool (poop) culture to look for parasites or inflammatory bowel disease.
Chest X-ray to look for signs of lung infections or erythema nodosum-associated diseases such as sarcoidosis.
Skin biopsy to remove a small piece of skin and look at it under a microscope.The doctor will usually only do a skin biopsy if they aren't yet sure that your symptoms are caused by erythema nodosum.
Erythema Nodosum Treatment
The treatment usually depends on what's causing it. For instance, if it's caused by an erythema nodosum-associated condition or infection, your doctor will treat that. If it's caused by a medication, your doctor will likely have you stop taking that medicine or switch you to a different one. But don't stop taking any medicine unless your doctor tells you to do so.
You can help manage your symptoms with some at-home therapies, such as:
- Use compression stockings or bandages to help with the swelling and pain.
- Rest and avoid hard activities.
- Lift the affected part of your body. For instance, put your legs on a pillow while you're lying down.
- Use NSAIDs to help with the swelling and pain.
Which Medications Treat Erythema Nodosum?
Medicines that may control your swelling and pain include:
- NSAIDs, like ibuprofen or naproxen. Be careful with these if you have inflammatory bowel disease (IBD) because they can make your IBD symptoms worse. Ask your doctor about what to take instead.
- Steroids, like prednisone. Your doctor may want to make sure you don't have a bacterial infection before they prescribe these because they can make an underlying infection worse.
- Hydroxychloroquine, cyclosporin A, or thalidomide, especially if you have IBD as an underlying condition.
- Potassium iodide or tetracycline, especially if you have symptoms that are hard to manage.Your doctor may want to make sure you don't have a thyroid disease before they prescribe potassium iodide because it can make thyroid disease worse.
- Colchicine, especially if you have Behcet's disease as an underlying condition.
Erythema Nodosum Prevention
Since many cases don't have a clear cause, it's hard to prevent all cases of erythema nodosum. But you can lower your risk of having a flare-up by doing the following:
- Avoid contact with people who are sick.
- Follow your doctor's treatment plan for any medical conditions you have.
- If possible, avoid medicines that cause erythema nodosum.
Erythema Nodosum Foods to Avoid
There are no studies specifically on diet changes to prevent a flare-up of erythema nodosum, but doctors recommend you have a healthy, well-balanced diet.
If you have IBD as an underlying condition, you may be able to avoid it if you don't eat foods that cause your IBD symptoms to flare up.