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Case Reports

Abstract

A 12-year-old female presented to the emergency department with multiple 1-2 cm tender nodular lesions over the bilateral upper and lower extremities as well as inability to ambulate secondary to worsening polyarthralgia. The skin lesions were clinically diagnosed as erythema nodosum when they appeared two months prior during treatment with amoxicillin for Group A Streptococcal (GAS) pharyngitis. Laboratory workup demonstrated elevated sedimentation rate, C-reactive protein, and anti-streptolysin O titers (>1,000). Clinical differential diagnoses included acute rheumatic fever, juvenile idiopathic arthritis, systemic lupus erythematosus, and post-streptococcal polyarteritis nodosa (PAN). A left thigh punch biopsy demonstrated a mid- to deep-dermal necrotizing vasculitis of mid-sized vessels with fibrin thrombi and an associated perivascular mixed inflammatory infiltrate with histiocytes, lymphocytes, eosinophils, and neutrophils. These features were consistent with a diagnosis of PAN. Computed tomography angiography failed to show involvement of large caliber vessels, and the patient was subsequently diagnosed with post-streptococcal cutaneous PAN (cPAN). Treatment with high-dose corticosteroids led to significant improvement of the patient’s symptoms, and she was discharged with plans for outpatient methotrexate therapy. Cutaneous PAN is a rare form of PAN limited to the skin, sometimes accompanied with musculoskeletal findings such as myalgias, arthralgias, and/or arthritis. In the pediatric population, the literature supports an association between cPAN and prior GAS infection. Herein, we share a case of pediatric post-streptococcal cPAN to serve as a reminder to practicing dermatologists and pathologists to consider cPAN as an uncommon sequela in children with a history of recent GAS pharyngitis.