When Fire and Ice Collide: A Rare Case of Idiopathic Angioedema with Dapsone-Induced Methemoglobinemia

Idiopathic angioedema is a potentially life-threatening cause of acute airway compromise, with reported mortality rates up to 30% when airway intervention is delayed. Methemoglobinemia, a dyshemoglobinemia that reduces hemoglobin's oxygen-carrying capacity, can be acquired from drugs such as dapsone and occurs in approximately 0.4-1% of exposed patients. The coexistence of these two entities is exceptionally rare, posing diagnostic and management challenges in the emergency setting.

A 16-year-old male presented to the emergency department with an acute onset swelling of the tongue and lips, accompanied by hypoxia. Endotracheal intubation was performed for airway protection. Adrenaline and fresh-frozen plasma were administered, resulting in the rapid resolution of angioedema. However, refractory hypoxia persisted despite adequate ventilation, normal point-of-care lung ultrasound, and unremarkable chest radiography. Arterial blood gas analysis revealed elevated methemoglobin levels (28%), confirming methemoglobinemia, attributed to recent dapsone use. Intravenous methylene blue was administered, leading to prompt normalization of oxygen saturation. The patient was extubated and discharged the following day without complications. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: This case underscores the importance of recognizing that more than one life-threatening condition can coexist in the same patient. Anchoring on a single diagnosis may delay identification of an equally dangerous concurrent pathology. Emergency physicians should maintain diagnostic vigilance, especially when expected improvement after treatment is incomplete or followed by unexplained deterioration. Timely recognition and targeted management of each condition can be lifesaving.