Acquired methemoglobinemia is a life-threatening cause of respiratory failure that occurs when there is an increase rate of oxidation of hemoglobin to methemoglobin resulting in greater affinity for oxygen binding and decreased release of oxygen to the tissues (1). Rasburicase is frequently used in patients with tumor lysis syndrome. Methemoglobinemia due to rasburicase occurs in fewer than 1% of patients (2). Usually, patients with glucose-6-phosphate dehydrogenase deficiency are at higher risk of developing rasburicase induced methemoglobinemia (1). This is a case report of rasburicase induced methemoglobinemia and the use of methylene blue.CASE PRESENTATION: 85-year-old African American female with past medical history of hypertension and CKD stage 3b who was admitted with altered mental status, decreased oral intake, and ongoing weakness. Her labs were significant for hyperuricemia, hypercalcemia, elevated LDH, acute on chronic kidney disease, 14% blasts on peripheral smear, and normocytic normochromic anemia. She was diagnosed with AML by bone marrow biopsy. Rasburicase was given for concern of tumor lysis syndrome. Two days later, the patient developed shortness of breath and hypoxia with pulse oxygen saturation of 70%. Arterial blood gas showed pH 7.429, PaCO2 29.2 mm hg, PaO2 99.9 mm hg, HCO3 18.9 mmol/L, methemoglobin 16.8%, O2 saturation 79.2%. She was treated with oxygen therapy and methylene blue. Rasburicase was determined to be the causative agent; thus, additional doses were not given. The methemoglobin level improved to normal over the course of several days.
DISCUSSION:The clinical presentation of methemoglobinemia may include gray pigmentation of the skin, chocolate colored blood, dyspnea and neurological symptoms, such as dizziness, headache, and seizures. These clinical symptoms vary with regards to methemoglobinemia concentrations and underlying medical conditions (3). For example, methemoglobinemia in patients with anemia usually present with more severe symptoms as they have reduced levels of hemoglobin (3). Methemoglobinemia is usually suspected based on history, symptoms, and hypoxemia refractory to supplemental oxygen (3). Blood gas with co-oximetry can be used to confirm the diagnosis (3). Methylene blue is usually used when methemoglobin levels exceed 20-30%; however, if the patient is symptomatic (ex. anxiety, light-headedness, or headaches) it should be used regardless of levels (3). Other treatment options include vitamin C and red blood cell exchange transfusion (1).
CONCLUSIONS:Diagnosis of methemoglobinemia relies on reviewing the patient's medication history, correlating clinical discrepancy on pulse oxygen saturation and arterial blood gas, and resolution of symptoms when the offending agent is discontinued. Careful evaluation of each case is pertinent when considering life-saving treatment, such as methylene blue.