Synopsis
Recognise erythema nodosum as a tender septal panniculitis across skin tones, investigate likely infectious, inflammatory, medicine and pregnancy triggers proportionately, and identify atypical nodules needing biopsy or urgent reassessment.
- Erythema nodosum causes crops of hot tender subcutaneous nodules, classically symmetrical over anterior shins, with poorly defined edges and no ulceration.
- Lesions evolve like bruises over several weeks from red or violaceous to brown, green-yellow or hyperpigmented and heal without atrophic scar.
- In brown or black skin, warmth, deep tenderness and swelling may identify active nodules more reliably than erythema; record residual pigment separately from pain and inflammation.
- Fever, malaise and bilateral ankle pain or periarticular swelling can precede or accompany the skin eruption.
- Common associations include recent streptococcal infection, sarcoidosis, tuberculosis, inflammatory bowel disease, pregnancy and selected medicines; many cases remain unexplained.
- Bilateral hilar lymphadenopathy with erythema nodosum and ankle periarthritis forms Löfgren syndrome, an acute sarcoid phenotype with a generally favourable course.
- First-line assessment is a focused history and examination plus FBC, inflammatory markers, throat and infection evaluation and chest imaging when the cause is not already secure.
- Biopsy is not required for a classic self-limited presentation; an atypical distribution, ulcer, persistent single nodule or diagnostic uncertainty needs a deep incisional sample containing subcutaneous fat.
- First-line treatment addresses the driver and uses rest, leg elevation, cool compresses and simple analgesia; an NSAID is appropriate only when renal, gastrointestinal, cardiovascular, pregnancy and IBD risk permits.
Key red flags
Unilateral rapid progression, marked systemic toxicity, fluctuance, necrosis, ulceration, calf swelling, absent pulses, severe breathlessness, immunosuppression, persistent fever, weight loss or nodules lasting beyond the expected course requires expedited alternative-diagnosis assessment.
Ulceration, drainage, marked asymmetry, livedoid change, cold tissue or a persistent solitary mass argues against ordinary erythema nodosum.
Investigation priorities
Prioritise the likely driver before ordering a broad low-yield panel.
Management branches
Tender lower-leg nodules appear over days with or without ankle symptoms.
- Palpate depth and borders, compare both legs and document heat, tenderness, colour, ulceration, fluctuance, pulses and calf asymmetry using photographs with consent.
- Ask about throat, chest, TB, bowel, pregnancy, medicine and constitutional clues and examine joints, nodes, chest and abdomen.
- Request FBC, inflammatory markers and chest radiography when unexplained, adding targeted throat, TB, pregnancy or bowel tests rather than a universal autoimmune screen.
The presentation is typical, circulation is intact and no urgent mimic is present.
- Reduce prolonged standing and impact exercise temporarily, elevate legs and use cool wet compresses while maintaining gentle movement as pain permits.
- Offer paracetamol or a short ibuprofen course only after checking renal, ulcer, bleeding, cardiovascular, asthma, IBD and pregnancy risk.
- Explain the expected bruise-like evolution and review within weeks, with earlier return for ulceration, unilateral spread, respiratory decline or systemic deterioration.