Beyond a routine blood gas, an easily picked but missed diagnosis of chronic Encephalopathy

Abstract

Recessive congenital methemoglobinemia (RCM) is a rare neurological disorder caused by a deficiency in NADH-CYB5R. RCM has two main types I&II, with cyanosis being the hallmark feature in both. Type-I is a mild form, with cyanosis being the only feature. While type-II is the severe form with prominent neurological symptoms including, dystonia and spasticity. However, the cyanosis is subtle and difficult to appreciate. The cyanosis in RCM is treated with ascorbic-acid or methylene-blue. However, those treatments will not alter the neurological complication. In this paper, we report two cases of RCM type-II in Saudi siblings. They presented with cyanosis at birth; a CO-oximetry was done showing a high level of methemoglobin and a trail of methylene blue was used. The siblings were followed up and showed signs of developmental delay, hypotonia, exaggerated reflex, and seizure. A genetic analysis was requested, which showed missense mutation (c.274 C > T), leading to amino acid substitution; p. Arg92Trp.

Keywords: Developmental delay; Methemoglobinemia; Microcephaly.

Fig. 1

T2 axial weighted magnetic resonance imaging (MRI) showing hypomyelination and hypoplasia of basal ganglia. Prominent extra-axial CSF spaces more prominent frontal and temporal regions. 1A and 1B is an axial and coronal section of B1 at 10 months. 1C and 1D is an axial and coronal section of B2 at three and a half months.