Allopurinol-Induced Eosinophilic Colitis as the Dominant and Initial Manifestation of Drug Reaction With Eosinophilia and Systemic Symptoms (DRESS) Syndrome

Drug reaction with eosinophilia and systemic symptoms (DRESS) is a rare, potentially life-threatening drug-induced hypersensitivity reaction. Although allopurinol is a well-recognized trigger and visceral involvement is common, gastrointestinal manifestations, particularly severe eosinophilic colitis as an initial presentation, are exceptionally uncommon. We report the case of a 70-year-old woman admitted in hypovolemic shock due to acute, profuse, non-bloody diarrhea. An extensive infectious workup was negative. Diagnostic clarification was achieved through colonoscopy, which demonstrated diffuse colonic inflammation, and histology revealed marked eosinophilic infiltration consistent with eosinophilic colitis. These findings, together with mild peripheral eosinophilia, acute kidney injury secondary to dehydration, and a subtle cutaneous rash, raised strong suspicion for DRESS syndrome. The diagnosis was supported by the recent initiation of allopurinol. This case underscores an unusual and severe gastrointestinal presentation of DRESS and highlights the importance of considering this diagnosis in patients with refractory diarrhea and eosinophilia, even in the absence of prominent skin involvement.