Infliximab-Associated IgA Vasculitis Masquerading as Crohn's Disease Relapse: Leukocytoclastic Vasculitis Confirmed on Duodenal Biopsy - A Case Report.

Introduction: Tumor necrosis factor (TNF)-α inhibitors are widely used in the management of inflammatory bowel disease (IBD), yet they can rarely provoke paradoxical immune-mediated complications such as vasculitis. Case Presentation: We describe the case of a 38-year-old man with ileocolonic Crohn's disease (CD) in remission during infliximab (IFX) maintenance therapy who presented with fever and diarrhea, raising the initial concerns of disease relapse. He subsequently developed severe abdominal pain, melena, and palpable purpura on his lower legs. Laboratory tests revealed elevated serum IgA and D-dimer levels, proteinuria, and microscopic hematuria. Video capsule endoscopy and colonoscopy revealed no active inflammatory lesions in the small or large bowels. However, an upper gastrointestinal (GI) endoscopy revealed multiple sharply circumscribed circular ulcers in the second portion of the duodenum. Histological assessment of biopsy specimens from the skin lesions and the duodenal ulcer base confirmed leukocytoclastic vasculitis. Based on the purpura and renal and GI involvement, IFX-associated IgA vasculitis was diagnosed. Withdrawal of IFX followed by oral prednisolone therapy and transition to ustekinumab led to rapid clinical recovery. Conclusion: This case highlights IgA vasculitis as a critical diagnostic consideration in patients with IBD receiving anti-TNF-α therapy who present with acute abdominal symptoms, especially when GI involvement precedes the appearance of purpura ("herald enteritis"). Biopsy of the duodenal ulcer base may provide decisive clues for differentiating vasculitis from CD relapse, thereby preventing inappropriate intensification of CD treatment.