Multimodal MR imaging in acute exacerbation of methylmalonic acidemia

Methylmalonic acidemia (MMA) is a disorder of methylmalonic acid metabolism caused by impaired methylmalonyl CoA mutase. Neuroimaging shows symmetric hypodensity on CT, and T2 prolongation on MRI in the globus pallidus; however, there have been only a few reports on MR spectroscopy findings and no previous reports on arterial spin labeling (ASL), both of which could reflect neurochemical derangement in MMA. We herein report an 18-month-old Sri Lankan boy presented with severe acute exacerbation of MMA due to bacteremia of Salmonella sp. O7. MRI on the seventh day showed T1 and T2 prolongation with decreased diffusion in the bilateral globus pallidus. ASL revealed hyperperfusion in the bilateral globus pallidus. MR spectroscopy showed increased choline (Cho), myo-inositol (mIns), glutamine (Gln), and lactate (Lac) in the globus pallidus; and increased Gln and Lac in the white matter. The globus pallidus is the site of high energy demand around the age of 1 year. In severe acute exacerbation of MMA, increased anaerobic metabolism due to impaired mitochondrial function may lead to hyperperfusion in the globus pallidus to compensate for a disturbed energy supply. Increased Cho, mIns, and Lac in the globus pallidus may result from active demyelination, astrogliosis, and increased anaerobic metabolism. Increased Gln in the basal ganglia and white matter may reflect excitotoxicity.