Paraneoplastic Myeloperoxidase (MPO)-Antineutrophil Cytoplasmic Antibody (ANCA)-Associated Vasculitis Revealing Colon Adenocarcinoma in a Patient With Controlled HIV Infection: A Case Report

The relationship between antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) and solid malignancies is uncommon and poses significant diagnostic challenges, particularly in individuals with underlying immune dysregulation, such as human immunodeficiency virus (HIV) infection. A 61-year-old man with well-controlled HIV infection presented with nephritic syndrome and palpable purpura. Laboratory evaluation revealed active urinary sediment and positive myeloperoxidase (MPO)-ANCA. Alternative causes of vasculitis were reasonably excluded based on clinical, serological, and histopathological evaluation. Skin biopsy demonstrated leukocytoclastic vasculitis, while renal biopsy showed pauci-immune necrotizing glomerulonephritis. During hospitalization, the patient developed hematochezia, for which a colonoscopy was performed, and a mass was identified in the ascending colon. Histopathological analysis confirmed stage IIIA colorectal adenocarcinoma. Treatment included glucocorticoids, plasmapheresis, and azathioprine, followed by right hemicolectomy and adjuvant CAPEOX chemotherapy. Partial improvement in the cutaneous lesions and glomerular filtration rate was observed following vasculitis-directed therapy, the patient achieved complete resolution of both the renal and cutaneous manifestations only after right hemicolectomy and adjuvant CAPEOX chemotherapy. This case is consistent with a possible paraneoplastic link between MPO-AAV and colorectal adenocarcinoma. In patients with HIV infection, distinguishing true vasculitis from incidental autoantibody positivity is challenging. The temporal relationship and improvement with cancer-directed therapy raise the possibility that malignancy may act as a trigger for clinically overt vasculitis. Recognition of this relationship may help guide appropriate management and avoid unnecessary or prolonged immunosuppression.