Recall urticaria caused by vedolizumab: case report and literature review.

Recall urticaria is a rare hypersensitivity phenomenon characterized by the reappearance of urticarial wheals strictly confined to previously exposed skin sites following systemic re-exposure to a trigger. Although reported with several drugs, its clinical features and underlying mechanisms remain poorly defined. A 25-year-old man with ulcerative colitis developed acute pruritic wheals localized exclusively to prior subcutaneous injection sites approximately 15 min after intravenous administration of vedolizumab. He had experienced repeated localized injection-site reactions during prior subcutaneous therapy. Histopathology revealed mild perivascular inflammation with eosinophils. The eruption resolved spontaneously within 24 h without systemic symptoms, and vedolizumab therapy was continued. This case represents the first report of vedolizumab-associated recall urticaria. A review of previously reported cases highlights strict site specificity as the defining feature, irrespective of the route or timing of re-exposure. Recall urticaria should be recognized as a site-specific hypersensitivity reaction distinct from systemic drug allergy.