methemoglobinemian

Methemoglobinemian is an uncommon variant spelling for methemoglobinemia, a medical condition characterized by an elevated level of methemoglobin in the blood. Methemoglobin forms when iron in hemoglobin is in the ferric (Fe3+) state and cannot bind oxygen effectively, reducing oxygen delivery to tissues. Normal methemoglobin levels are typically less than 1-2% of total hemoglobin; higher levels can cause symptoms, with severity correlating to the percentage present.

Causes are divided into acquired and congenital categories. Acquired methemoglobinemia results from exposure to oxidizing agents such as nitrites and nitrates, certain antibiotics and local anesthetics, benzocaine, dapsone, aniline dyes, or contaminated water. Congenital forms arise from deficiencies in the enzyme system that reduces methemoglobin back to functional hemoglobin (NADH-cytochrome b5 reductase) or from abnormal hemoglobin variants (hemoglobin M).

Symptoms include cyanosis (bluish or slate-gray skin) that does not fully improve with oxygen, headache, dizziness, fatigue, tachycardia, shortness of breath, and in severe cases altered mental status or seizures. Blood may appear chocolate-brown rather than bright red. Diagnosis typically shows a discrepancy between a normal arterial partial pressure of oxygen (PaO2) and low oxygen saturation on pulse oximetry, with confirmation by co-oximetry showing elevated methemoglobin levels.

Treatment depends on severity. Mild cases may resolve after removing the offending agent and providing supplemental oxygen. Significant cases or symptomatic patients are treated with methylene blue as a reducing agent, unless G6PD deficiency is present. Alternatives include high-dose ascorbic acid or, in refractory or congenital cases, chronic management strategies. Prognosis improves with timely diagnosis and treatment.