Very late stent thrombosis associated with stent malapposition and uncovered struts after contrast-enhanced CT in a patient receiving long-term steroid therapy due to Kounis syndrome: a case report.

Background: Kounis syndrome (KS) is an acute coronary syndrome triggered by allergic or hypersensitivity reactions and is classified into three variants: coronary vasospasm, plaque rupture, and stent thrombosis. Type III KS involving stent thrombosis is extremely rare. The mechanisms linking allergic triggers with very late stent thrombosis (VLST) remain insufficiently characterized. Case summary: We present a rare case of Type III KS triggered by contrast media in a 74-year-old man with a history of everolimus-eluting stent implantation ∼1 year and 10 months prior to presentation and chronic corticosteroid therapy for membranous nephropathy. Shortly after a contrast-enhanced computed tomography scan, the patient developed an ST-elevated myocardial infarction. Optical frequency-domain imaging revealed a heavy thrombus burden, malapposed stent struts, and uncovered struts. The drug-induced lymphocyte stimulation test was positive for iopamidol, confirming contrast-induced KS. Discussion: This case highlights the potential interplay between mechanical vulnerability (malapposition and uncovered struts) and allergic responses in the pathogenesis of VLST. Chronic corticosteroid therapy may have delayed vascular healing, contributing to persistent uncovered struts. The combination of stent-related factors and systemic hypersensitivity likely promoted thrombus formation. Physicians should consider KS in the differential diagnosis of stent thrombosis even if it occurs long after percutaneous coronary intervention or if the patient is receiving long-term corticosteroid therapy.