Definition
Erythema nodosum is the name given to extremely tender lumps on the legs and sometimes the arms. They are caused by inflammation of the fat beneath the skin. The bumps look like bruises. They change color in the same way, from pink to blue to brown. They are often accompanied by fever, joint pain, and redness around the eyes. They may continue to erupt for a week to 10 days. They will eventually resolve. It often resolves within 1-2 months.
Causes
Erythema nodosum is thought to be a type of allergic reaction. It may be caused by:
- Infections
- Streptococcal infections ( strep throat, tonsillitis, rheumatic fever)
- Various viral infections (eg, infectious mononucleosis and hepatitis B)
- Tuberculosis
- Fungal lung infections (coccidioidomycosis, histoplasmosis)
- Psittacosis (parrot fever)
- Lymphogranuloma venereum (an uncommon sexually transmitted disease)
- Leprosy (Hansen’s disease)
- Inflammatory conditions
- Ulcerative colitis
- Crohn’s disease
- Sarcoidosis
- Medications
- Sulfa drugs
- Iodides
- Bromides
- Birth control pills
- Unknown causes
Risk Factors
This condition is rare. Having any of the causes listed above will only slightly increase your risk of the disorder. It is more common in:
- Young adults (20-30 years old)
- Females
Symptoms
If you have some of these, do not assume it is erythema nodosum. Have your doctor examine any sores.
- Very tender deep-seated lumps, like bruises, usually located on your shins
- Associated joint pain and fever
Diagnosis
Your doctor will ask about your symptoms and medical history. A physical exam will be done. You may be referred to a doctor that focuses in skin problems (dermatology) or infectious diseases.
Tests may include the following:
- Blood and urine samples
- Cultures of various bodily fluids
- Chest x-ray and other imaging tests
- PPD (skin test for tuberculosis)
- Biopsy of a lesion—a sample is taken to be examined under a microscope
Treatment
If a cause can be identified, it will be treated. For the nodules themselves, pain relief is all that is needed. They tend to resolve on their own in about six weeks. They will not cause scarring. Treatment options include the following:
Pain Relief
- Bedrest and elevation of legs
- Wet compresses
- Aspirin or similar nonsteroidal anti-inflammatory
- Potassium iodide
- 300-600 milligrams per day for up to two months may alleviate the discomfort (but iodides can also cause the problem)
Steroid Treatment
This may be necessary in severe cases.
Prevention
Some of the causes can be avoided. The condition is rare enough that nothing but the most obvious measures are worthwhile.