Severe Treatment-Resistant Methemoglobinemia of Unknown Etiology With Recurrence

Introduction: Methamoglobinemia is a condition characterized by impaired oxygen delivery to the tissues due to the formation of methemoglobin (Met-Hb). Diagnosis is established when Met-Hb levels exceed 5%. Levels over 30% are associated with severe symptoms and can be life-threatening. Pulse oximetry may provide misleading readings, often reporting oxygen saturation around 85%, irrespective of actual oxygenation levels. Management involves discontinuing offending agents, providing supportive care, and use of specific treatment agents. Most commonly, cases report a quick and effective recovery following treatment. Case Presentation: We describe a case of a patient requiring four separate admissions over a 9-month period, all for methemoglobinemia, where the cause remained uncertain. A 25-year-old female was admitted to the intensive care unit (ICU) with sudden onset shortness of breath and cyanosis, and Met-Hb level 55.5%, suspected due to dapsone. She was treated with 1 mg/kg of methylene blue intravenously. Met-Hb levels remained persistently above 20% for a number of days, and reaccumulated following initial decline. Repeated doses of methylene blue were required, and activated charcoal was given. She was readmitted 3 days later, with reaccumulation of Met-Hb. This was again thought secondary to dapsone, given the long half-life of dapsone and potential for enterohepatic recirculation. She had a third admission with methemoglobinemia almost 2 months after the first admission, and again 8 months later. Suggestion was that azathioprine could be the causative agent; however, this has not been reported previously. Discussion: We report a case of a 25-year-old female with repeated admissions with methemoglobinemia. This case highlights the potential for refractory methemoglobinemia requiring repeated treatment, and the importance of longer periods of close observation. It is important to consider the diagnosis in patients without a clear trigger for methemoglobinemia, as an identifiable cause may not always be clear.