What Is Erythema Nodosum?
Erythema nodosum (EN) is an inflammatory skin condition that causes tender, painful red or purple bumps, typically on the shins. EN is a type of panniculitis, which is inflammation of the fatty layer under the skin.
EN is not a disease in itself but usually a sign of another condition, or a hypersensitivity (allergic) reaction to a drug.
Erythema nodosum is not the same as erythema nodosum leprosum (ENL), which is a complication of a disease called leprosy.
What Causes Erythema Nodosum?
About half of all cases of erythema nodosum have no known cause (they are called idiopathic), but the following conditions commonly trigger erythema nodosum:
Ringworm is caused by a fungus.
What Are Risk Factors for Erythema Nodosum?
Risk factors for erythema nodosum include infections, medications, pregnancy, cancer, and inflammatory conditions.
What Are Erythema Nodosum Symptoms and Signs?
The main symptom of erythema nodosum is painful, tender red or purple raised bumps (nodules) on the shins. Bumps may also appear on the thighs, ankles, buttocks, calves, arms, upper body, or face. The nodules are firm, develop over several days, are usually slightly raised, and about 2 to 5 centimeters in diameter.
Other symptoms of EN include
- joint swelling, redness, or pain that accompany the nodules, and
- enlarged lymph nodes in the chest.
Before the EN nodules appear, a prodrome of symptoms may occur such as
- joint pain,
- upper respiratory infection symptoms, and
- feeling unwell (malaise).
How Do Medical Professionals Diagnose Erythema Nodosum?
Usually, a medical professionals can make a diagnosis of erythema nodosum during a physical examination and history. There is no specific lab test that would indicate EN. Usually, a doctor will check for illnesses that may cause EN and order tests to find the cause. Testing for underlying conditions may include
- blood tests,
- skin or blood test for tuberculosis,
- throat culture to test for strep,
- chest X-ray, and
- skin sample biopsy.
What Are Treatments and Home Remedies for Erythema Nodosum?
Erythema nodosum usually does not need treatment. EN typically goes away when an individual receives treatment for the condition that causes it. Medications to treat erythema nodosum include the following:
- Nonsteroidal anti-inflammatory pain medications (NSAIDs)
- Potassium iodide (not recommended in patients with tuberculosis)
- Oral corticosteroids (doctors may prescribe a short course if EN is severe and debilitating)
Home remedies may relieve EN pain and discomfort:
- Elevating the legs
- Compression stockings
- Applying ice wrapped in a towel to the affected area
What Are Complications of Erythema Nodosum?
A rare type of erythema nodosum is a chronic form called erythema nodosum migrans that may flare up intermittently over several years. The inflammation with chronic EN tends to be less severe than with classic EN.
However, for the most part, complications associated with erythema nodosum are those resulting from the underlying condition that causes the EN.
What Is the Prognosis for Erythema Nodosum?
The prognosis for erythema nodosum is good, and usually EN will resolve spontaneously within a few weeks. As the EN nodules heal, the bumps will get smaller and start to look like bruises. Recovery time is about two to eight weeks and the healed nodules do not leave scars.
About one-third of patients with underlying chronic illnesses may have a relapse of EN.
Is It Possible to Prevent Erythema Nodosum?
There is no way to prevent erythema nodosum. Sometimes you can prevent the underlying cause, but since about half the cases of EN have no known cause (are idiopathic), there is no way to prevent it.
Reviewed on 12/10/2018
Kroshinsky, Daniela. "Erythema nodosum." UpToDate.com. November 2018.
Massachusetts General Hospital. "Erythema Nodosum."