is a potentially fatal condition characterized by elevated levels of
methemoglobin in the blood leading to tissue hypoxia. Methemoglobinemia is
considered a rare cause of cyanosis and thus the history taking and its
clinical correlation is of paramount importance for rapid detection of the
disease and immediate treatment of the same.
35-year-old moderately built female patient presented to the E.R with a 3 day
history of progressive fatigue and 1 day history of breathlessness and bluish
discolouration of lips. History of dyspnea on work with no associated chest
pain, palpitations, orthopnoea or PND. There was no history of recent respiratory
infections, cold exposures and congenital heart disease. On enquiring further,
we learnt that the patient had visited her dermatologist 6 months back and was
started on Prednisolone 20mg and Dapsone 200mg for treatment of Lichen Planus.
Patient has a regular menstrual history and no history of cardiac diseases,
Type-2 diabetes mellitus, systemic hypertension, Bronchial asthma and seizure
disorder. On examination, patient was comfortable in supine position. Cyanosis
of lips was present. The vital were Pulse- 90/minute, regular, normal volume.
B.P- 120/80 mm of Hg. Temperature- 98 F, Respiratory Rate- 24/min, Saturation with
a digital pulse oximeter showed 70% in room air. Cardiovascular, Respiratory, abdominal
examination and Central nervous system were normal. Althogh the patient was immediately
started on nasal 5L/min of nasal O2, the patient’s saturation did not improve. In view of low saturation, an arterial blood
gas was done which revealed a chocolate-brown blood with an oxygen saturation
of 99%, Ph-7.38, PO2- 99mm Hg, PCO2- 16mm Hg and Bicarbonate
level was 22 mmol/L . The Haemoglobin was 10.2g%. A diagnosis of methemoglobinemia
secondary to Dapsone use was suspected and Serum levels of methemoglobin was
found to be 7.3%. Patient was immediately started on Methylene Blue and the
saturation level started increasing gradually over hours.
being a sulfone antibiotic is a inhibitor of folate synthesis. It is
metabolized in the liver by cytochrome P450 leading to adverse hematological
complications like hemolysis, methemoglobinemia and is also involved in various drug
interactions. Even though it was traditionally used for the treatment of
leprosy, Dapsone is also sometimes used for the treatment of dermatological
conditions. In this case, the diagnosis of methemoglobinemia was suspected purely
based on clear history of dapsone use in addition to the “saturation gap”