Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.
2 min synopsisUK scopeSources checked 27 Aug 2026Clinical review pending
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Toxic, ulcerating or vascular mimic
Shock, severe pain out of proportion, crepitus, rapidly spreading unilateral inflammation, a cold swollen limb, purpura, ulceration or major respiratory compromise is not typical uncomplicated erythema nodosum and may represent deep infection, thrombosis, vasculitis or another panniculitis.
Action: Arrange same-day emergency assessment with sepsis treatment, vascular imaging or specialist tissue sampling directed by the threat; do not inject corticosteroid or reassure on the basis of tender nodules alone.
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.
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.
Atypical destructive nodule
Ulceration, drainage, marked asymmetry, livedoid change, cold tissue or a persistent solitary mass argues against ordinary erythema nodosum.
Investigation priorities
01
Focused exposure and medicine historyFirst step
Prioritise the likely driver before ordering a broad low-yield panel.
Management branches
First diagnostic sequenceConfirm the nodule behaves like erythema nodosum
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.
The presentation is typical, circulation is intact and no urgent mimic is present.
Key medicines
Ibuprofen for short-term painTake 400 mg by mouth with or after food up to three times daily for the shortest necessary period, leaving at least four hours between doses and not exceeding 1200 mg daily without prescription.
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.