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Erythema nodosum

Daniela Kroshinsky, MD
Section Editor
Jeffrey Callen, MD, FACP, FAAD
Deputy Editors
Abena O Ofori, MD
Paul L Romain, MD


Erythema nodosum (EN) is a delayed-type hypersensitivity reaction that most often presents as erythematous, tender nodules on the shins (picture 1A-D). Common triggers for EN include infection, drugs, pregnancy, malignancy, and inflammatory conditions, such as sarcoidosis or gastrointestinal diseases; however, many cases are idiopathic (table 1). The characteristic histologic finding in EN is a septal panniculitis without vasculitis.

EN usually resolves spontaneously within several weeks. When necessary, treatment can be given to reduce symptoms or hasten resolution.

The etiologies, diagnosis, and management of EN will be reviewed here. Other forms of panniculitis and erythema nodosum leprosum (a complication of leprosy that is also known as a type 2 reaction) are reviewed separately. (See "Panniculitis: Recognition and diagnosis" and "Epidemiology, microbiology, clinical manifestations, and diagnosis of leprosy", section on 'Type 2 reaction'.)


EN occurs in all ages, sexes, and racial groups but is most common in women in their second to fourth decades [1]. Women are affected three to six times more often than men. The specific incidence of EN varies based upon the local prevalence of the associated triggering diseases [2]. (See 'Etiology' below.)


EN is considered a delayed-type hypersensitivity reaction resulting from exposure to various antigens; however, the pathogenesis is not fully understood. The pathogenic mechanism may involve immune complex deposition in the septal venules of the subcutaneous fat, neutrophil recruitment with resulting reactive oxygen species formation, tumor necrosis factor (TNF)-alpha production, and granuloma formation [3-5].

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Literature review current through: Nov 2017. | This topic last updated: Nov 30, 2016.
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