key: cord-1054408-mmyhm4kf
authors: Shah, Preet Mukesh; Hingolikar, Ankita; Dhakre, Vijay Waman
title: An Unexpected Cause of Dyspnea Caused by Dapsone-Induced Methemoglobinemia
date: 2020-09-24
journal: Chonnam Med J
DOI: 10.4068/cmj.2020.56.3.204
sha: 6d1fbd0e32682a6e91133ac939517c67e41cb748
doc_id: 1054408
cord_uid: mmyhm4kf

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An 18-year-old girl presented with a 7 day history of worsening shortness of breath. No history of fever, chest pain, hemoptysis, orthopnea, palpitations, or any contact with known/suspected Covid-19 individuals was reported. She had a background of recurrent oral ulceration (secondary to an unclassified autoimmune condition), for which she had been on dapsone and prednisolone for the past 5 years. The ambulance doctor found her to be hypoxic (on pulse oximetry) with an oxygen saturation of 84%. She was started on oxygen and was brought to the emergency department. A systemic examination was normal. Her arterial blood gas sample had a "chocolate" colour to it (Fig. 1) , and the analysis (on 6 L/min oxygen) showed pO2 of 27.2 kPa (normally 11-14 kPa), pCO2 of 3.6 kPa (normally 4.6-6.4 kPa), bicarbonate of 23.9 mmol/L (normally 22-29 mmol/L), oxygen saturation of 95%. Despite a good saturation and pO2, she was still tachypneic. A COVID19 throat swab was sent off (which later turned out to be negative). Chest X-ray was also normal. Considering a possibility of pulmonary embolism, Computerised Tomography Pulmonary Angiogram (CTPA) was requested, which was normal. She was still feeling fatigued and breathless. With the current Covid-19 pandemic, considering this to be early hypoxic respiratory failure, the intensive care team was called for and they planned to intubate her; when she was reviewed by the medical team, who noted that on her arterial blood gas result, her methemoglobin levels were 14.4% (normally up to 1.5%). Believing her symptoms to be secondary to methemoglobinemia secondary to dapsone, intubation was deferred, and methylene blue was administered. Arterial blood gases were monitored periodically which showed a gradual reduction in methemoglobin levels.

Methemoglobinemia is a disorder of oxygen carrying capacity of haemoglobin, being rare but potentially fatal. 1 Methemoglobin is an oxidized form of haemoglobin which leads to altered oxygen binding capacity. It is formed when ferrous ions within the heme moiety are oxidized to ferric ions, which aren't able to bind oxygen molecules. Accumulation of methemoglobin causes a leftward shift of the oxygen-haemoglobin dissociation curve, causing decreased oxygenation of tissues. Clinically seen cases are acquired due to drugs, including dapsone and chemical exposure. Oxidative metabolites of dapsone are responsible for methemoglobinemia. 2 Physiologically, a normal level of methemoglobin is up to 1.5%. Clinical presentation depends on methamoglobin levels, ranging from asymptomatic cases, to confusion, cardiovascular collapse, and death. Cyanosis develops when serum methemoglobin levels exceeds 15%. Levels of 30-45% result in headache, fatigue, tachycardia and dizziness. When levels exceed 60%, it leads to arrhythmias, dyspnoea, seizures and coma. Death usually occurs at methemoglobin levels greater than 70%. 3 Treatment is supportive, with discontinuation of the offending drug. Symptomatic patients require administration of methylene blue.

Preet Mukesh Shah, et al

Understanding acquired methemoglobinemia

Acquired methemoglobinemia: a retrospective series of 138 cases at 2 teaching hospitals

Pathophysiologic mechanisms, diagnosis, and management of dapsone-induced methemoglobinemia

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None declared.