Methimazole-induced agranulocytosis complicated by sepsis and ileocolic intussusception: a case report and literature review

Abstract Background Methimazole (MMI) is a primary pharmacological treatment for autoimmune thyrotoxicosis, but it carries a risk of agranulocytosis—a rare yet severe adverse effect that can lead to life-threatening infections due to profound immunosuppression. This case report aims to present and analyze an unusual instance of MMI-induced agranulocytosis complicated by severe sepsis and secondary ileocolic intussusception. Case presentation A 36-year-old female with thyrotoxicosis of uncertain etiology was admitted with fever, pharyngitis, abdominal pain, and diarrhea after one month of MMI therapy. Laboratory evaluation revealed severe agranulocytosis (absolute neutrophil count 0.01 × 10⁹/L) and significantly elevated inflammatory markers. Imaging confirmed ileocolic intussusception with transmural intestinal necrosis. The patient underwent an emergency ileocolic resection and temporary ileostomy, followed by comprehensive multidisciplinary management, including broad-spectrum antibiotics, G-CSF, and multi-organ support. Conclusion This case describes ileocolic intussusception occurring in the setting of severe methimazole-induced agranulocytosis and uncontrolled systemic sepsis, a rare severe complication of methimazole therapy. It highlights the critical need for vigilant hematologic monitoring and suggests that in cases of septic shock secondary to intestinal necrosis, emergency surgical source control can be life-saving and should not be absolutely contraindicated by profound neutropenia. A multidisciplinary approach is essential for successful outcomes. Clinical trial number Not applicable.