Congenital Methemoglobinemia in a 33-Year-Old Patient: A Case Report on a Rare Presentation and a Review of the Literature.

Cyanosis and dyspnea are common complaints in adults and have broad differential diagnoses, of which rare ones such as congenital methemoglobinemia should always be considered in the differential diagnosis. Methemoglobinemia might be acquired or congenital. Patients' symptoms vary from severe shortness of breath, mental status changes, and cyanosis to none. The diagnosis of congenital methemoglobinemia is challenging and requires high index of suspension, especially in older patients. In addition, when diagnosed the treatment of congenital methemoglobinemia is oral ascorbic acid which is readily available. We present a rare case of a 33-year-old lady, who had a long history of recurrent episodes of cyanosis, headache, and fatigue. After excluding cardiopulmonary causes, methemoglobin levels were measured and found to be high, and the chart review revealed high levels of methemoglobin in all her previous episodes, without exposure to any offending agent. This raised the concern of a late diagnosis of congenital methemoglobinemia. The patient was treated with a high dose of ascorbic acid resulting in resolution of the symptoms. Congenital methemoglobinemia is a rare diagnosis that needs a high index of suspicion, especially in adults. A thorough history, physical examination, and multiple laboratory tests are needed to confirm the diagnosis and rule out other causes.