SHM Converge Scientific Abstract ePoster Gallery-Thinking Outside the Thorax - A Case of Dapsone-Induced Methemoglobinemia

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This case report describes a 64-year-old man who developed dapsone-induced methemoglobinemia after recent hospitalization for pulmonary embolism and viral constrictive pericarditis. He presented with dyspnea, cyanosis, confusion, hypotension, and low oxygen saturation that remained “stuck” at 88–90% despite high-flow 100% oxygen. Initial evaluation, including CBC/CMP, EKG, chest X-ray, echocardiogram, and CTA chest, did not reveal a structural cardiopulmonary cause.<br /><br />Because of his recent thoracic history, the team initially focused on recurrent structural pathology. However, chart review later revealed that he had started dapsone three weeks earlier for Pneumocystis jirovecii pneumonia prophylaxis while receiving high-dose prednisone. An arterial blood gas showed a markedly elevated methemoglobin level of 20.9%, confirming the diagnosis of acquired methemoglobinemia.<br /><br />Methemoglobinemia occurs when hemoglobin iron is oxidized from the ferrous (Fe2+) to ferric (Fe3+) state, reducing oxygen delivery and causing functional anemia. It can produce cyanosis and hypoxia with a normal or elevated PaO2. Common acquired causes include dapsone, topical anesthetics, antimalarial drugs, sulfonamides, rasburicase, and nitrates. Congenital forms are usually due to autosomal recessive CYB5R3 mutations.<br /><br />The patient was treated with methylene blue and vitamin C, dapsone was discontinued and listed as an allergy, and he made a full recovery. He was successfully weaned off oxygen and discharged on atovaquone for continued PJP prophylaxis.<br /><br />The report emphasizes the importance of thorough medication reconciliation and avoiding anchoring bias when evaluating unexplained hypoxia, especially in patients with complex recent hospitalizations.

Asset Subtitle

Megan C. Ohlfest

Meta Tag

Author List Megan C. Ohlfest, Rita Poon

Category Clinical Vignettes

Concept Methemoglobinemia

Concept Hemoglobin

Concept Iron oxidation state

Concept Dapsone

Concept CYB5R3

Distinguished Non-Finalist

Presenter Organization MedStar Georgetown University Hospital

Presenting Author Megan C. Ohlfest

Track Adult

Keywords

dapsone

methemoglobinemia

cyanosis

hypoxia

methylene blue

Pneumocystis jirovecii pneumonia

medication reconciliation

anchoring bias

pulmonary embolism

constrictive pericarditis

Methemoglobinemia

Hemoglobin

Iron oxidation state

Dapsone

CYB5R3