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Erythema nodosum and panniculitis
Erythema nodosum (EN) is the most common panniculitis: a hypersensitivity reaction of the fat septa that presents as red, warm, painful nodules on the shins, resolves without ulceration or scarring, and requires a search for the cause.
Why it matters in the exam
Exam stems show a young woman with painful nodules on the shins and ask for the likely cause and the work-up: streptococcal pharyngitis, pregnancy and oral contraceptives, sarcoidosis, inflammatory bowel disease, tuberculosis, drugs and local infectious disease. The question also separates EN from other panniculitides: nodular vasculitis (erythema induratum) on the back of the calves, which ulcerates and is linked to tuberculosis, pancreatic panniculitis with fat necrosis, and lupus panniculitis. Remember the "bruise that moves" — EN fades like a bruise, changing from red to purple to yellow-green over weeks. Many stems also include fever and joint pain, and signs of bowel inflammation, pregnancy and infection should be sought. Treatment includes rest, leg elevation, NSAIDs and treating the cause, and potassium iodide in prolonged cases. In the exam, note the site of the nodules, any ulceration, age and sex, and any story of infection, drug, pregnancy or bowel symptoms, because these are the clues that point to the cause and the next test. A deep biopsy that includes fat is needed only when the clinical picture is atypical.
Key points
- Erythema nodosum is the most common panniculitis and appears as painful nodules on the front of the shins.
- Common causes are streptococcus, pregnancy and contraceptives, sarcoidosis, inflammatory bowel disease, tuberculosis and drugs, and in some cases no cause is found.
- The work-up includes blood count, inflammatory markers, streptococcal tests, chest X-ray and a pregnancy test.
- Nodular vasculitis appears on the back of the calves, ulcerates and is linked to tuberculosis.
- EN is treated with rest, leg elevation, NSAIDs and treating the cause, and it resolves without scarring.
Summary table
| Type | Site and appearance | Main causes | Distinction and treatment |
|---|---|---|---|
| Erythema nodosum | Painful red nodules on the front of both shins, no ulceration | Streptococcus, pregnancy and contraceptives, sarcoidosis, IBD, tuberculosis, drugs | Septal panniculitis; rest, NSAIDs, treat the cause |
| Nodular vasculitis (erythema induratum) | Nodules on the back of the calves, ulcerating, women | Tuberculosis (hypersensitivity) | Lobular panniculitis with vasculitis; treat tuberculosis |
| Pancreatic panniculitis | Nodules with oily discharge, anywhere | Pancreatitis or pancreatic cancer | Fat necrosis with "ghost cells"; raised lipase |
| Lupus panniculitis | Nodules on the arms, face and thighs that leave depressions | Lupus | Hydroxychloroquine |
| Cold or traumatic panniculitis | After cold exposure (children, ice lolly) or injury | Physical | Resolves; reassurance |
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Sources
- British Association of Dermatologists clinical guidance on panniculitis, 2021 — Erythema nodosum
- Fitzpatrick's Dermatology, 9th edition (2019) — Panniculitis
- ECCO guidelines on extraintestinal manifestations of inflammatory bowel disease, 2024 — Skin
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.