Erythema nodosum versus nodular vasculitis.
BACKGROUND: Erythema nodosum (EN) is usually considered to be a septal panniculitis, and nodular vasculitis (NV) a lobular panniculitis. We tested the usefulness of this histologic classification in clarifying a frequent clinical dilemma: EN versus NV. METHODS: Over 3 years 109 patients with panniculitis were included in this study. After a history and a physical examination, a clinical diagnosis was made according to well-established criteria. RESULTS: From the study of 88 patients, we concluded that in the clinically typical cases, the clinico-pathologic agreement was 93% and 94% for EN and NV respectively, whereas it diminished to 79%, 72%, and 67% in the cases clinically diagnosed as EN migrans, atypical EN, and atypical NV, respectively. Moreover, septal and lobular panniculitis were always two clear-cut, different, opposite patterns of hypodermal inflammation to these conditions. CONCLUSIONS: In the absence of a known pathogenetic mechanism, the histopathology remains the most objective discriminating marker between EN and NV, mainly in the clinically atypical and doubtful cases.