Recognizing Drug-Induced Methemoglobinemia in the Emergency Setting: A Case of Topical Dapsone Toxicity

Methemoglobinemia is an uncommon but important cause of hypoxia, most often triggered by exposure to certain medications or chemicals. Although rarely encountered in clinical practice, it can be life-threatening if not promptly recognized and treated. The condition occurs when methemoglobin levels in the blood exceed the normal physiological threshold of 1-2%. Even mild elevations can produce symptoms such as persistent headaches, dizziness, lethargy, and central cyanosis. As methemoglobin concentrations increase, the risk of severe hypoxic injury rises, with critically high levels capable of causing coma, arrhythmias, or death. We report the case of a 21-year-old previously healthy female who developed methemoglobinemia secondary to dapsone therapy. She presented with a two-week history of worsening headaches and palpitations, accompanied by several days of progressive shortness of breath. The absence of underlying cardiopulmonary or systemic disease initially complicated the diagnostic process. This case highlights the essential role of comprehensive history-taking in the evaluation of hypoxic patients, particularly younger individuals without apparent risk factors. A detailed review of the patient's medication history ultimately identified dapsone use as the precipitating factor. This report serves as a reminder for clinicians to maintain a broad differential diagnosis when assessing unexplained hypoxia and to consider rare but reversible causes, such as methemoglobinemia, in the appropriate clinical context.