Erythema Nodosum
Erythema nodosum is a type of panniculitis (inflammation of the subcutaneous fat), characterised by painful, erythematous nodules on the anterior shin.
This updated UKMLA guide is based on NICE CKS, which covers causes, symptoms, diagnosis, and management.
Causes and Risk Factors
Erythema nodosum is idiopathic in 1/3 cases
Other causes:
- Infective
- Streptococcal infections (often URTI) – account for 10-30% cases in adults
- Tuberculosis
- Mycoplasma, Yersinia, leprosy, GI infections
- Pregnancy
- Autoimmune conditions (e.g. sarcoidosis, Behcet’s disease)
- IBD (Crohn’s disease and ulcerative colitis)
- Drugs
- Sulphonamides
- Hepatitis B vaccine
- Isotretinoin
- SSRI
- COCP
- Antibiotics
- Malignancy (mainly haematological) – rare
Epidemiology
Much more common in females than in males
Most common in 15-45 y/o
Clinical Features and Diagnosis
Erythema nodosum is primarily a clinical diagnosis based on clinical features:
- Painful lesions
- Most commonly in the lower limbs (knee, shins, ankle)
- Bilateral and symmetrical
- Tender, erythematous, warm nodules and plaques (raised)
- Most patients are systemically well, but fever, malaise, and arthralgia are possible
Over time, the lesions become purple and then fade as a bruise (the lesions tend to last 3-6 weeks)
Tests to investigate for underlying causes:
- Throat swab and ASO titre for Streptococcus
- Urinalysis
- Blood tests (FBC and inflammatory markers)
- Chest X-ray to check for tuberculosis and sarcoidosis
In atypical cases (e.g. lesions not on the lower limbs, persisting lesions, ulceration), elliptical biopsy may be needed to confirm the diagnosis (typical finding: septal panniculitis without vasculitis)
Management
Treat any underlying causes and stop any causative medications (if possible)
Otherwise, conservative management:
- Reassure that most cases regress spontaneously in 3-4 weeks
- Limit physical exercise and bed rest (esp. if there is marked leg swelling)
- NSAIDs for pain