Atypical and Typical Presentation of Erythema Nodosum: Clinical Differences in Treatment and Outcome

Introduction: Erythema nodosum (EN) is the most common form of panniculitis that predominantly affects the shins. While EN in atypical sites has been described by many authors, there are currently only case studies published on this topic. This study aimed to evaluate clinical differences between patients suffering from EN on the shins, compared to patients with EN in atypical locations. Methods: We analyzed 105 patients in a retrospective, single-center study at a university hospital in Switzerland. Typical EN was defined as lesions, found only on the lower legs, while atypical EN as lesions on the upper legs, trunk, arms, or face, only or in addition to lesions on the lower legs. The patients were assessed for age, gender, dermatologic history, time until first medical consultation, time to diagnosis, and time until remission. Further, etiology, symptoms, and applied therapies were investigated. Findings were then compared between the typical and atypical EN cohorts. Results: Overall, we included 70 patients (37.99 +/- 15.67 [3-81] years) with EN solely on the shins and 35 patients (41.27 +/- 16.85 [9-76] years) with EN on other locations. Interestingly, time until diagnosis was significantly shorter in atypical EN (p = 0.034, 1.14 +/- 4.68 vs. 0.46 +/- 1.14 months). Time to remission was similar in both groups (3.61 +/- 2.73 vs. 3.05 +/- 2.86 months, respectively). Sarcoidosis was the only etiologic factor significantly more frequent in atypical EN compared to typical EN (23% vs. 9%, p = 0.042). Besides that, solely subtle differences were seen regarding etiology, gender, age at onset, course of the disease, and symptoms. Conclusions: Our study suggests that only minor alterations between both study populations exist. Significant differences were found in time to diagnosis (shorter for atypical EN), as well as in sarcoidosis as an etiologic factor (more frequent in atypical EN). While adalimumab was only prescribed in atypical EN cases, prognosis seems to be similar for typical and atypical EN (similar time to remission, similar amount of reoccurring cases). Due to the limited sample size, however, our study population may have been too small to detect the relevant differences, and bigger studies may be needed.