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Skin-nontumor / Clinical Dermatology

Other dermatoses

Erythema nodosum

Reviewer: Mowafak Hamodat MB.CH.B, MSc., FRCPC, Eastern Health, St. Johns (Canada (see Reviewers page)
Revised: 25 July 2011, last major update July 2011
Copyright: (c) 2002-2010, PathologyOutlines.com, Inc.

Definition
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● Panniculitis with tender red nodules, usually on both shins

Clinical features
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● Red, painful, bilateral, symmetrical nodules, elevated above the skin surface
● On anterior surface of legs, arms, face, calves and trunk
● Usually involutes in days/weeks, leaving depressed, pigmented lesions
● No ulceration
● Immune mediated, but precise mechanism is unknown
● May be associated with streptococcus infection, tuberculosis, sarcoidosis, coccidioidomycosis, ulcerative colitis, Behcet’s disease, drug reactions or idiopathic; also Hodgkin lymphoma, renal cell carcinoma and carcinomas of colon, pancreas and uterine cervix

Terminology
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● Erythema nodosum migrans (subacute nodular migratory panniculitis, migratory panniculitis): asymmetrical, unilateral, and distributed solely on the legs; marked female predominance; older age group
● Chronic erythema nodosum: nodules appear over months/years; otherwise indistinguishable from typical condition

Clinical images
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Erythematous nodules and plaques on anterior legs; patient had also ulcerative colitis

Early erythema nodosum in young woman taking birth control pills

Micro descriptions
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● A prototype of septal panniculitis, characterized by vascular changes, septal inflammation, hemorrhage and variable acute and chronic panniculitis
● Both septal and lobular panniculitis
● Marked septal fibrosis, infiltrated by lymphocytes, neutrophils, histiocytes and granulomas with giant cells
● Septal infiltrate spills over to affect the fat lobules
● Dermis shows perivascular and periadnexal chronic inflammatory cell infiltrate
● Early, the septal inflammation is acute and characterized by neutrophils, soon replaced by lymphocytes and histiocytes
● Variable eosinophils, variable vasculitis
● Miescher’s radial granuloma: characteristic finding of erythema nodosum; septal collection of histiocytes surrounding a cleft (appear to look like spaces); reported in Sweet’s syndrome, nodular vasculitis and necrobiotic lipodica

Micro images
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Perivascular infiltrate

Inflammatory infiltrate extending along fibrous septa of adipose tissue

Septal panniculitis and Miescher's granulomata

Differential Diagnosis
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● Nodular vasculitis or subacute nodular migratory panniculitis: usually septal
● Weber-Christian disease associated panniculitis: usually lobular inflammation

Additional references
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● More information

End of Skin-nontumor / Clinical Dermatology > Other dermatoses > Erythema nodosum

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