characterized by tender, red or violet, palpable, subcutaneous nodules on the shins and occasionally other locations. It often occurs with an underlying systemic disease, notably streptococcal infections, sarcoidosis, and inflammatory bowel disease. Diagnosis is by clinical evaluation and sometimes biopsy. Treatment depends on the cause.Erythema nodosum primarily affects people in their 20s and 30s but can occur at any age; women are more often affected.
Etiology of Erythema Nodosum
Etiology of erythema nodosum is unknown, but an immunologic reaction is suspected because erythema nodosum is frequently accompanied by other disorders. The most common accompanying disorders are
Other possible triggers include
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Other bacterial infections (eg, Yersinia Plague and Other Yersinia Infections Plague is caused by the gram-negative bacterium Yersinia pestis. Symptoms are either severe pneumonia or massive lymphadenopathy with high fever, often progressing to septicemia. Diagnosis is... read more
, Salmonella Overview of Salmonella Infections The genus Salmonella is divided into 2 species, S. enterica and S. bongori, which include > 2400 known serotypes. Some of these serotypes are named. In such cases, common usage sometimes shortens... read more , mycoplasma Mycoplasmas Mycoplasmas are ubiquitous bacteria that differ from other prokaryotes in that they lack a cell wall. Mycoplasma pneumoniae is a common cause of pneumonia, particularly community-acquired pneumonia... read more , chlamydia Chlamydia Three species of Chlamydia cause human disease, including sexually transmitted infections and respiratory infections. All are susceptible to macrolides (eg, azithromycin), tetracyclines (eg... read more , leprosy Leprosy Leprosy is a chronic infection usually caused by the acid-fast bacilli Mycobacterium leprae, which has a unique tropism for peripheral nerves, skin, and mucous membranes of the upper respiratory... read more 
, lymphogranuloma venereum Lymphogranuloma Venereum (LGV) Lymphogranuloma venereum (LGV) is a disease caused by 3 unique strains of Chlamydia trachomatis and characterized by a small, often asymptomatic skin lesion, followed by regional lymphadenopathy... read more , tuberculosis Tuberculosis (TB) Tuberculosis (TB) is a chronic, progressive mycobacterial infection, often with a period of latency following initial infection. TB most commonly affects the lungs. Symptoms include productive... read more 
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Fungal infections (eg, kerion Kerion Tinea capitis is a dermatophyte infection of the scalp. Diagnosis is by clinical appearance and by examination of plucked hairs or hairs and scale on potassium hydroxide wet mount. Treatment... read more
, coccidioidomycosis Coccidioidomycosis Coccidioidomycosis is a pulmonary or hematogenously spread disseminated disease caused by the fungi Coccidioides immitis and C. posadasii; it usually occurs as an acute benign asymptomatic or... read more 
, blastomycosis Blastomycosis Blastomycosis is a pulmonary disease caused by inhaling spores of the dimorphic fungus Blastomyces dermatitidis. Occasionally, the fungi spread hematogenously, causing extrapulmonary disease... read more 
, histoplasmosis Histoplasmosis Histoplasmosis is a pulmonary and hematogenous disease caused by Histoplasma capsulatum; it is often chronic and usually follows an asymptomatic primary infection. Symptoms are those of pneumonia... read more 
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Viral infections (eg, Epstein-Barr Infectious Mononucleosis Infectious mononucleosis is caused by Epstein-Barr virus (EBV, human herpesvirus type 4) and is characterized by fatigue, fever, pharyngitis, and lymphadenopathy. Fatigue may persist weeks or... read more
, hepatitis B Hepatitis B, Acute Hepatitis B is caused by a DNA virus that is often parenterally transmitted. It causes typical symptoms of viral hepatitis, including anorexia, malaise, and jaundice. Fulminant hepatitis and... read more ) -
Use of drugs (eg, sulfonamides, iodides, bromides, oral contraceptives)
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Hematologic and solid cancers
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Pregnancy
Up to one third of cases of erythema nodosum are idiopathic.
Erythema induratum, a similar disorder, manifests with lesions on the calves and classically affects patients with tuberculosis.
Symptoms and Signs of Erythema Nodosum
Erythema nodosum is a subset of panniculitis Panniculitis Panniculitis describes inflammation of the subcutaneous fat that can result from multiple causes. Diagnosis is by clinical evaluation and biopsy. Treatment depends on the cause. (See also Erythema... read more that manifests as erythematous, tender nodules or plaques, primarily in the pretibial region, often preceded or accompanied by fever, malaise, and arthralgia. Lesions may be detected more easily by palpation than inspection and can evolve into bruiselike areas over weeks.
Diagnosis of Erythema Nodosum
Diagnosis of erythema nodosum is usually by clinical appearance and can be confirmed by excisional biopsy of a nodule when necessary. A diagnosis of erythema nodosum should prompt evaluation for causes. Evaluation might include biopsy, tuberculosis skin testing (PPD or anergy panel), antinuclear antibodies, complete blood count, chest x-ray, and serial antistreptolysin O titers or a pharyngeal culture. Erythrocyte sedimentation rate is often high.
Treatment of Erythema Nodosum
Erythema nodosum almost always resolves spontaneously. Treatment includes bed rest, elevation, cool compresses, and nonsteroidal anti-inflammatory drugs. Potassium iodide 300 to 500 mg orally 3 times a day can be given to decrease inflammation. Systemic corticosteroids are effective but should be used only as a last resort because they can worsen an occult infection.
If an underlying disorder is identified, it should be treated.
Key Points
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The most common causes of erythema nodosum are streptococcal infections (particularly in children), sarcoidosis, and inflammatory bowel disease.
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Diagnose erythema nodosum primarily by clinical appearance but, when necessary, excise a nodule for biopsy confirmation.
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Treat erythema nodosum supportively and use nonsteroidal anti-inflammatory drugs or potassium iodide as needed until the disorder resolves spontaneously.
