Erythema nodosum
Also called septal panniculitis, EN
A reactive inflammation of the subcutaneous fat septa: tender, warm, red nodules on the shins that bruise as they fade and never ulcerate. The skin is the messenger; the cause (streptococcal infection, sarcoidosis, inflammatory bowel disease, drugs, pregnancy, tuberculosis) is the question.
How it looks
Multiple tender, ill-defined, erythematous to violaceous subcutaneous nodules over both shins, without ulceration.
Rose is the lesion, grey the pattern the lesions make, green where on the body it lives.
Across skin tones
On deeply pigmented skin the erythema is muted and the nodules are found by palpation and warmth; the bruise-like evolution reads as deeper brown rather than yellow-green.
Don't miss
Erythema nodosum with bilateral hilar adenopathy and ankle arthritis is Loefgren syndrome, an acute sarcoidosis with a good prognosis that still needs a chest radiograph.
Symptoms & course
- Tender nodules that hurt to touch and to walk on
- Fever, malaise and arthralgia, especially of the ankles
- Lesions evolve like bruises over two to six weeks
Diagnostic approach
- Throat swab and antistreptolysin titre
- Chest radiograph for hilar adenopathy (sarcoidosis, tuberculosis)
- Pregnancy test, inflammatory bowel symptoms and drug history
Differential, and how to separate them
- Cellulitis
Favours it: A hot, red, swollen leg
Against it: Cellulitis is unilateral and confluent; erythema nodosum is bilateral, nodular and does not spread by the hour
- Cutaneous small-vessel vasculitis
Favours it: Palpable purpura on the legs
Against it: Vasculitis lesions are purpuric and may ulcerate; erythema nodosum nodules are deep, tender and never break down
Management principles
- Treat or remove the cause
- Rest, leg elevation, compression and non-steroidal anti-inflammatory drugs
- Potassium iodide or a short steroid course for persistent disease once infection is excluded
Clinical pearl: Nodules on the shins that never ulcerate and fade like bruises: septal panniculitis until proven otherwise.
Clinical pearl: The skin diagnosis takes a minute; the search for the cause takes the rest of the consultation.
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