Background: Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune rheumatic disease characterized by mononuclear cell infiltration and destruction of small and medium-sized blood vessels, leading to severe end-organ damage such as glomerulonephritis and diffuse alveolar hemorrhage. Since the pandemic started, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has been shown to induce or exacerbate autoimmune diseases.This report aims to inform healthcare providers about the clinical features of a pediatric case of a newly diagnosed patient with AAV following COVID-19 infection.Case Presentation Summary: In February 2025, an 8-year-old girl presented with a rash for two days in the setting of worsening bilateral lower extremity edema and pain for 2 months. The rash was petechial and purpuric, non-blanching, and non-painful on the soles and dorsal aspects of the feet, scattered along the ankles, legs up to the bilateral hips, sparing the areas above the hips.Initial evaluation suggested that the rash was most suspicious for a viral infection such as hand-foot-mouth disease, but also resembled Henoch-Schonlein purpura with its distinct lower extremity distribution and edema of the dorsal aspects of the hands and feet. The patient was admitted to the pediatric floor due to inability to ambulate with pain, and infectious disease and dermatology consultations were requested.After a comprehensive infectious workup was done, dermatology offered a skin biopsy to guide the diagnosis, which mom declined. Oral prednisolone 0.5 mg/kg/day for 5 days was prescribed because of the rash’s quick progress and severe joint pain that prevented the patient from ambulation. Rash and myalgias have significantly improved with steroid use over 24 hours. She was then discharged home on the same dose of prednisolone.However, once the 5-day course of oral prednisolone was finished, the feet started to become painful again, and new lesions appeared on the legs. She then presented to the rheumatology clinic and was prescribed more long-term prednisolone with a slow tapering schedule. She was given 0.25 mg/kg/day prednisolone daily and naproxen 10 mg/kg BID continuously over the next 2 weeks.The rash did not completely resolve. Due to the lack of improvement, rheumatology performed an assessment, suspecting an onset of autoimmune disorder, and a lab workup was performed.The laboratory workup revealed the presence of ANCA antibody (proteinase-3), isolated low C4, normal immunoglobulins, and elevated sedimentation rate. Urinalysis revealed mild proteinuria, small hematuria, positive leukocyte esterase, and 100 WBC/hpf, along with 11-30 RBC/hpf. Protein/creatine ratio in spot urine was 577 mg/g. COVID-19 IgG, nucleocapsid antibody was positive, along with the presence of lupus coagulant. ANCA-associated vasculitis was considered; subsequently, a renal biopsy was performed, which showed evidence of crescentic glomerulonephritis, consistent with ANCA-associated vasculitis. The patient was never vaccinated for COVID-19, although other immunizations were up to date.Learning Points Discussion: It is crucial to maintain a high index of suspicion to identify autoimmune phenomena following COVID-19 infection in unvaccinated individuals, which aids in early detection and intervention to prevent systemic organ involvement and complications.
