Background: Acquired methemoglobinemia is an uncommon but potentially life-threatening cause of hypoxia in emergency practice, produced when oxidant exposures convert hemoglobin iron from the ferrous (Fe 2+ ) to the ferric (Fe 3+ ) state, impairing oxygen delivery.Naphthalene, a component of household mothballs, can produce both methemoglobinemia and severe oxidative hemolysis; intentional ingestion in adults is rare and may present with delayed, dramatic deterioration.Case presentation: We report a case of a 28-year-old man who presented 48 hours after intentional ingestion of naphthalene mothballs with progressive central cyanosis, altered sensorium, and dyspnea.Pulse oximetry remained 85% despite high-flow oxygen, and arterial blood gas (ABG) analysis showed a high PaO, producing a clear "saturation gap." CO-oximetry confirmed methemoglobinemia at 45%, and laboratory investigations demonstrated severe intravascular hemolysis with Hb of 7.2 gm/dL, very high lactate dehydrogenase (LDH), undetectable haptoglobin, and indirect hyperbilirubinemia.The patient received emergent intravenous methylene blue (1 mg/kg) with rapid clinical improvement, CO-oximetry normalization, and supportive management, including blood transfusion and hydration for acute kidney injury.He recovered and was discharged after a monitored inpatient course.Conclusion: This case highlights the diagnostic utility of the saturation gap and chocolate-brown blood appearance, the life-saving role of timely methylene blue therapy, and the need to anticipate hemolysis and renal injury in naphthalene toxicity.Early recognition and coordinated emergency and critical care interventions are essential to avoid morbidity and mortality.
KV et al. (Mon,) studied this question.