Not All That Itches Is DRESS: A Case Report of Lichenified Dermatosis and Hypereosinophilia Associated With Tocilizumab

Drug-induced hypereosinophilic syndromes (HESs) have been associated with a variety of medications, including biologic agents. We present a case of an 85-year-old female with a history of giant cell arteritis (GCA) complicated by ascending aortic aneurysm and aortitis, who developed marked peripheral eosinophilia (peaking at 3710/µL) and a persistent pruritic papular rash during long-term tocilizumab therapy. Extensive infectious, hematologic, and immunologic evaluations were unrevealing. While the clinical picture raised concern for a drug-induced hypersensitivity reaction, histopathology was more consistent with lichen simplex chronicus, and there was no evidence of systemic organ involvement. Her eosinophilia and cutaneous symptoms improved significantly after discontinuing tocilizumab, implicating the drug as a possible trigger. This case highlights the diagnostic challenges in distinguishing drug reaction with eosinophilia and systemic symptoms (DRESS) from other drug-induced or idiopathic dermatoses in patients receiving biologic therapy and underscores the importance of clinicopathologic correlation in guiding management.