Diagnosis: Erythema nodosum or not?

Erythema nodosum is the final common pathway to a myriad of insults and is thought to be a hypersensitivity reaction centered in the subcutis, To reco gnize the histological spectrum of erythema nodosum, one must be aware of t he morphologic chronology of the disease (early, fully developed, late) and its clinical variants (erythema nodosum migrans), This article reviews the range of changes that can be seen in this prototype of a septal panniculit is and describes the diversity that may be accepted in the diagnosis, Diffe rential diagnoses at each stage of disease development are discussed. The c riteria elaborated should assist the pathologist in answering the clinician 's query, "Erythema nodosum, or not?" Copyright (C) 1999 by W.B. Saunders C ompany.