Abstract We present a case of an 18-year-old male with history of mild autism and intermittent asthma who presented to the emergency department (ED) for evaluation of hypoxemia. Primary care provider noted low oxygen saturation (SpO2) and he was sent to the ED for evaluation. Patient noted that on his activity watch he was having SpO2 in the 70’s to 80’s for the prior 2 years and with normal heart rate between 50-80 beats per minute. He had no symptoms of cough or dyspnea on exertion. He was born full-term and was hospitalized for treatment of neonatal meningitis. He did not have respiratory complications at birth. He was diagnosed with asthma during childhood. He is currently in community college. There was no inhalant use and no concerning environmental exposures. At our ED, oxygen saturation was 88-92% and did not improve with use of supplemental oxygen of 4L provided via nonrebreather. A chest x-ray was obtained which showed peribronchial thickening. Pulmonary was consulted to evaluate for causes of hypoxemia. Given the presentation we were concerned for shunt physiology due to an arteriovenous malformation (AVM). The CTA showed slightly more prominent peripheral pulmonary vessels, no AVMs, and no evidence of significant parenchymal lung disease. CBC revealed slight erythrocytosis and was otherwise normal. VBG was also normal. An ABG revealed elevated pO2 of 107 (O2 saturation 98%) which revealed a elevated saturation gap of 9% compared to the simultaneously SpO2 monitor oxygen saturation of 89%. This data became worrisome for a problem with the hemoglobin itself. Co-oximetry revealed a methemoglobin level of 22.6%. Given the lack of exogenous exposure history, genetics was consulted and obtained single gene sequencing with deletion and duplication analysis for CYB5R3, which resulted in the pathogenic homozygous mutation c.775CT (p.Arg259Trp). Congenital methemoglobinemia is a rare disorder that is often missed and can present from infancy to late adulthood. Congenital methemoglobinemia Type 1 is the condition where the CYB5R defect is expressed only on erythrocytes. Congenital methemoglobinemia Type 2 occurs when all somatic cells express the defect which results in a severe, incurable form of epileptic encephalopathy associated with neurodegeneration and severe intellectual disability 1. It is important for pulmonologists to be aware of this rare disorder which presents with hypoxemia. References 1. Bouatrous E, et al. Identification of High-Risk Single Nucleotide Polymorphisms in the Human CYB5R3 Gene Responsible for Recessive Congenital Methemoglobinemia: A Computational Approach. Mol Syndromol. 2023 Oct;14(5):375-393. This abstract is funded by: None
Paris et al. (Fri,) studied this question.