Post-streptococcal erythema nodosum

Erythema Nodosum (EN) is the most common panniculitis, presented as acutely eruptive painful erythematous nodules on lower extremities symmetrically, with a wide spectrum etiology from infection to malignancy. The aim of this case report is to comprehend the diagnosis and the underlying treatable origin of EN. A 24-year-old female presented with painful red bumps on both legs a week after an episode of fever and sore throath. She also noted tenderness on both ankle joints. She was diagnosed with vasculitis by the internist and was treated with Methylprednisolone (MP) 16mg/day for 2 weeks. The symptomps were resolved but re-emmerged 1 week after the MP was stopped. Physical examination revealed erythematous nodules on both legs with tenderness on palpation. ASTO test was positive. Septal panniculitis and Miescher’s granuloma was identified through histopathology examination. Exclusion of inflammatory subcutaneous differential diagnosis such as EN, nodular vasculitis (NV), and cutaneous polyarteritis nodosa (CPAN) require clinical and histopathologic consideration. Etiology identification of EN was done through a relevant supporting examination based on epidemiology, history, and physical examination. Post-streptococcal EN possibly related to molecular mimicry and immune complex deposition leading to reactive inflammation. Hereby we reported one case of post-streptococcal EN that was confirmed by laboratory examination and skin biopsy. The clinical response was good towards the etiology-based treatment.