Etiological factors and histopathological features in erythema nodosum: a 6-year retrospective cross-sectional study

Introduction: Erythema nodosum (EN) is the most common type of panniculitis. The most frequent etiological factors are streptococcal pharyngitis, sarcoidosis, Behcet's disease, and tuberculosis. Our objective was to identify the etiological factors and to evaluate the patients' clinical, laboratory, and histopathological findings. Methods: Eighty-eight patients diagnosed with EN at our clinic between 2013 and 2019 were evaluated retrospectively. Sixty-five patients were evaluated histopathologically. Results: The patients' ages ranged between 17 and 76 (mean age: 41.91 +/- 13.07 years). EN was 7.8 times more frequent in women. Patients presenting with idiopathic EN were significantly older than secondary cases (p < 0.05). Sixty-one patients (69.3%) had an underlying disease (secondary EN). The most common etiological factors were upper respiratory tract infections (n = 26), followed by Behcet's disease (n = 20). Septal panniculitis was present in 89.2% of cases evaluated histopathologically. Mixed or lobular panniculitis was present in 35.7% of Behcet's disease patients with EN-like lesions. Vasculitis was also noted in 35.7% of Behcet's disease patients. Conclusions: Our data confirm the predominance of upper respiratory tract infections and Behcet's disease among patients with EN in Turkey. Behcet's disease patients presenting with EN-like lesions may show mixed panniculitis and vasculitis, whereas classic EN patients predominantly show septal panniculitis.