A Diagnostic Pitfall: Carbamazepine-Induced Drug Reaction With Eosinophilia and Systemic Symptoms (DRESS) Syndrome Masquerading As Angiotensin-Converting Enzyme Inhibitor Angioedema.

Drug reaction with eosinophilia and systemic symptoms (DRESS), also known as drug-induced hypersensitivity syndrome (DIHS), is a severe, multiorgan, delayed hypersensitivity reaction with significant morbidity. Diagnosis is often delayed due to its mimicry of other conditions. We present the case of a 69-year-old Hispanic male with hypertension and stage two chronic kidney disease who developed trigeminal neuralgia and was started on carbamazepine. Approximately seven weeks later, he presented with a generalized rash, angioedema, and mucosal swelling, initially attributed to his concurrent lisinopril therapy. Despite discontinuation of lisinopril and treatment with corticosteroids and antihistamines, his condition progressed with new systemic symptoms, including paresthesia, dysgeusia, polydipsia, polyuria, and weight loss. The progression of symptoms despite this intervention was the pivotal diagnostic clue. Hospital admission revealed marked eosinophilia (8.9 percent), mild transaminitis, and a diffuse erythrodermic rash involving more than 90 percent of his body surface area. A diagnosis of probable DRESS syndrome (RegiSCAR score six) secondary to carbamazepine was made. Immediate discontinuation of carbamazepine and initiation of intravenous corticosteroids led to rapid clinical and laboratory improvement. He was discharged on a prolonged oral steroid taper with complete resolution at follow-up. This case underscores the critical importance of considering DRESS in any patient with a rash and systemic symptoms occurring two to eight weeks after initiation of a high-risk drug, even in the presence of other potential culprits. It highlights that clinical progression despite withdrawal of one suspected agent should prompt urgent re-evaluation for an alternative etiology, such as DRESS.