Methemoglobinemia: The Guthrie Clinic Experience

Background: Methemoglobinemia is a very rare condition that can be either congenital or acquired. It causes tissue hypoxia by reducing the capacity of hemoglobin to transport oxygen. In this study, we conducted a retrospective analysis of the etiology, clinical characteristics, treatment modalities, and outcomes of patients with methemoglobinemia who were evaluated at our institution over a span of 25 years. Methods: We conducted a retrospective review of medical records from 33 consecutive patients diagnosed with methemoglobinemia and followed at our hospital between 2000 and 2025. Results: The median age was 53 years (range 1-93), and 27 patients (82%) were female. The median methemoglobin (MetHb) level was 11.7% (range 2.1%-50.6%). The cause of methemoglobinemia was congenital in 10 patients (30%) and acquired in 23 (70%). Among the congenital cases, the underlying genetic abnormalities were nicotinamide adenine dinucleotide reductase deficiency (2 patients), hemoglobin M disease (2 patients), and unidentified (6 patients). In the acquired cases, the causative agents were dapsone (10 patients), phenazopyridine (4 patients), lidocaine (4 patients), sulfamethoxazole/trimethoprim (2 patients), benzocaine (1 patient), and unidentified (2 patients). Treatment modalities included oxygen supplementation, vitamin C, methylene blue, and observation. Over a median follow-up of 6 years, no deaths were attributed directly to methemoglobinemia. Conclusions: In our cohort, the most common cause of methemoglobinemia was acquired, and the most common causative agent was dapsone. All cases of acquired methemoglobinemia were successfully treated with prompt discontinuation of the offending agent, along with oxygen supplementation, vitamin C, and methylene blue.