By Gary M. White, MD
Erythema nodosum (EN) is the most common panniculitis and may develop in response to a wide variety of antigens. In this unique reaction pattern, exquisitely tender nodules develop on the shins. See also Vilanova Disease.
The typical patient experiences the acute onset of multiple deep-seated, red nodules on both shins. Pain is often severe. Some patients limp or can't even walk. It usually runs its course over 3-6 weeks. Lesions on the thighs or arms are less common. Sweet's syndrome, Behcet Syndrome and cryoglobulinemia can cause lesions which resemble EN [AD 1999;135;62]. There is a a chronic variant also known as Vilanova disease that may present as a solitary, slowly enlarging red plaque on the lower leg.
The most important first step is to determine, if possible, the cause. Any of a variety of antigen exposures may be implicated.
Infections: Group A beta-haemolytic Streptococcus, Yersinia, Salmonella, Campylobacter, Mycobacterium tuberculosis, Epstein–Barr virus, Parvovirus B19, Cytomegalovirus, Dermatophytes, Hepatitis, Blastomycosis, Histoplasmosis, Coccidioidomycosis, Sporothrix, non-specific URI, chlamydia
Drugs: Oral contraceptives, Macrolides, Cephalosporin, Penicillin, BRAF inhibitor therapy [JEADV 2015 Sep;29:1797-806]
Inflammatory diseases: Behçet's disease, Sarcoidosis, Ulcerative colitis, Crohn's disease
Others: Hodgkin's disease, pregnancy, radiation of a neoplasm [BJD 1999;140;372].
In most cases, a skin biopsy is not needed for diagnosis but may be helpful in atypical cases. A high fever, respiratory symptoms and/or an abnormal chest X-ray may signal a causative lung process, e.g. pneumonia. Workup may include CBC, u.a., ASO, throat culture, PPD, CXR, yersinia titers, liver enzymes, stool culture if diarrhea is present and intradermal or serologic tests for deep fungi.
Mild cases may only require rest and NSAIDs, e.g., indomethacin. More severe cases often respond to SSKI (supersaturated potassium iodide). It is often supplied with a dropper calibrated with lines labeled 0.3 cc. and 0.6 cc. Initially, it may be dosed 0.3 TID-QID and increased to 0.6 TID-QID. If the pain is severe and there is no evidence of ongoing infection, prednisone, e.g., 1 mg/kg, is very effective in controlling the outbreak within several days. Narcotic analgesics may be needed for the pain. Rarely, patients will need a wheelchair at home because of the pain. Recurrent EN has been treated successfully with hydroxychloroquine 200 mg QD [BJD 1996;134;373]. If the lesions are not very numerous, some have injected the lesions with IL Kenalog 5-10 mg/cc.
EN does occur in children [PD 1996;13;447]. In one series, idiopathic, Streptococcus and Yersinia were common causes. Mycoplasma pneumoniae infection may be found.
Erythema nodosum from coccidioidomycosis.
Vilanova Disease or erythema nodosum migrans.
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