Erythema nodosum !
Erythema nodosum causes tender red lumps under the skin of the shins, as a reaction to an infection, drug, pregnancy or another disease.
Updated 2026-11-01
Structures involved
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Why it happens
What it is
The most common form of panniculitis: a delayed hypersensitivity reaction in the subcutaneous fat producing tender, red, warm nodules, usually on both shins. It is a sign of an underlying trigger in about half of cases.
Who gets it
Most frequent in young adult women (20–45 years). In Colombia and Latin America, tuberculosis, streptococcal infection, leprosy (erythema nodosum leprosum) and deep fungal infections such as histoplasmosis are causes to consider, alongside sarcoidosis and inflammatory bowel disease.
Causes
- Idiopathic in many cases
- Infections: streptococcal pharyngitis (most common in children), tuberculosis, Yersinia, Salmonella, Campylobacter, histoplasmosis, coccidioidomycosis, leprosy
- Sarcoidosis (Löfgren syndrome) and inflammatory bowel disease (Crohn disease, ulcerative colitis); Behçet disease
- Drugs: oral contraceptives and oestrogens, sulfonamides, penicillins
- Pregnancy; less often lymphoma and other cancers
Risk factors
- Female sex and age 20–45
- Recent sore throat or diarrhoeal illness
- Exposure to tuberculosis or endemic fungi
- Pregnancy or oestrogen-containing medicines
Pathophysiology
A trigger antigen provokes a delayed (type IV) hypersensitivity reaction with immune complexes in the septa between fat lobules of the subcutis. Neutrophils and later lymphocytes and histiocytes infiltrate the septa without vasculitis (septal panniculitis without vasculitis). Over time, nodules fade through bruise-like colour changes and resolve without ulcers or scarring.
Classification
- Acute erythema nodosum (most cases), resolving within weeks
- Chronic or migratory forms
- Erythema nodosum leprosum (type 2 reaction in lepromatous leprosy), a distinct entity
Symptoms and signs
- Sudden crop of tender, warm, red nodules 1–5 cm, usually bilateral on the shins
- Nodules not ulcerating, felt better than seen
- Colour changes over days from red to violet to yellow-green, like a bruise (erythema contusiformis)
- Fever, malaise, arthralgia (especially ankles) before or with the nodules
- Ankle swelling
- Symptoms of the trigger: sore throat, cough, diarrhoea
Diagnosis
- Clinical
- Clinical diagnosis based on tender bilateral pretibial nodules; history focused on recent infections, drugs, pregnancy, gut and lung symptoms.
- Tests
- Full blood count, ESR or CRP, throat culture and ASO titre, tuberculin skin test or interferon-gamma release assay, pregnancy test, stool tests if diarrhoea. Deep incisional biopsy including fat if atypical: septal panniculitis without vasculitis.
- Imaging
- Chest X-ray in every case to look for bilateral hilar lymphadenopathy (sarcoidosis) or tuberculosis.
Differential diagnosis
- Erythema induratum (nodular vasculitis, calves, ulcerates, linked to tuberculosis)
- Cellulitis
- Superficial thrombophlebitis and deep vein thrombosis
- Cutaneous polyarteritis nodosa and other vasculitis
- Lupus panniculitis, pancreatic panniculitis, insect bites
Goal of treatment
Find and treat the underlying cause, relieve pain and inflammation while nodules resolve, and withdraw any triggering drug.
Treatment
- Conservative
- Rest, leg elevation and compression stockings to reduce pain and swelling.
- Medical
- NSAIDs for pain and inflammation (avoided in inflammatory bowel disease flares and pregnancy); potassium iodide in persistent cases.
- Medical
- Treat the cause: antibiotics for streptococcal infection, anti-tuberculosis therapy, management of sarcoidosis or IBD; stop oral contraceptives or culprit drugs.
- Medical
- Systemic corticosteroids for severe cases only after infection, especially tuberculosis, has been excluded.
Complications
- Recurrence if the trigger persists
- Complications of the underlying disease (tuberculosis, sarcoidosis, IBD)
- Nodules heal without scarring or atrophy
Prognosis
Self-limited: nodules usually resolve in 3–6 weeks without scarring. Outlook depends on the underlying cause; Löfgren syndrome has a good prognosis.
Test yourself
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What is the histological pattern of erythema nodosum?
Septal panniculitis without vasculitis.
Which imaging test is part of the work-up of every patient with erythema nodosum?
Chest X-ray, looking for bilateral hilar lymphadenopathy (sarcoidosis) or tuberculosis.
What is Löfgren syndrome?
Acute sarcoidosis with erythema nodosum, bilateral hilar lymphadenopathy, fever and arthritis, usually ankles; good prognosis.
What is the most common identifiable cause of erythema nodosum in children?
Streptococcal pharyngitis.
Do erythema nodosum nodules ulcerate or scar?
No; they fade like a bruise and heal without ulceration or scarring.
Related conditions
- Sarcoidosis
- Tuberculosis
- Crohn disease
- Ulcerative colitis
- Streptococcal pharyngitis
- Behçet disease
- Histoplasmosis
- Leprosy (Hansen disease)
- Cellulitis of the leg
- Deep vein thrombosis
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Erythema nodosum (MedlinePlus, US National Library of Medicine, 2026).
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