Anti-neutrophil Cytoplasmic Antibody-Associated Vasculitis Presenting With Disseminated Streptococcus constellatus Pyogenic Infection.

Infections and autoimmunity exhibit a two-way alternate interaction. This report aims to present the case of severe disseminated sepsis leading to the diagnosis of antineutrophil cytoplasmic antibody (ANCA)-positive granulomatosis with polyangiitis. A 49-year-old male presented with fever, anemia, septic polyarthritis, bilateral pulmonary infiltrates with associated acute respiratory distress syndrome, deep vein thrombosis, and acute renal failure. Streptococcus constellatus was isolated from blood cultures and joint aspirates. Despite the initiation of targeted treatment, improvement was marginal; respiratory tract involvement worsened, and a parapneumonic fluid collection developed. The patient was investigated for immune system dysregulation. Investigation for hematological abnormalities or neoplasia was negative. An autoimmune antibody profile revealed high positivity for proteinase 3 cytoplasmic-ANCAs. Corticosteroids and rituximab were administered with a good clinical response. Although, in this case, the triggering of autoimmunity through a longstanding infection cannot be ruled out, the persistence of symptomatology despite control of the infection indicates the presence of an underlying autoimmune disease. Patients with ANCA-associated vasculitis are often diagnosed in the context of an infection, which can be encountered especially in the initial period after diagnosis. Accurate differential diagnosis is important to ensure appropriate treatment.