Four children, 4-13 yrs old, with methylmalonic acidemia who developed acute dystonia after metabolic decompensation with ketoacidosis are reported from the Department of Pediatrics, University of Pennsylvania School of Medicine, and the Children’s Hospital of Philadelphia, PA, and other collaborating institutions. The neurological complications were the result of acute necrosis of the globus pallidus and some involvement of internal capsules. One patient, aged 5 yrs, was a poor feeder and had vomited soon after birth. She was hospitalized at 1 wk of age with lethargy and ketoacidosis, and had massive amounts of methylmalonic acid in the urine that were not reduced by IM cyanocobalamin. Treatment with long-term oral alkali, and a diet restricted in isoleucine, valine, methionine, and threonine resulted in improvement and normal growth and development up to 2 yrs of age when she had an acute “metabolic stroke“ precipitated by otitis media. Subsequently, she developed dystonia, dysarthria, dysphagia, and spastic quadriplegia. A CT scan showed bilateral symmetric lucencies of the globus pallidus and internal capsules. The lesions were thought to result from deranged organic acid metabolism and accumulation of toxic metabolites in the brain. 
COMMENT. Lesions of the basal ganglia have been noted in other inborn errors of organic acid metabolism, including propionic acidemia, and glutaric aciduria type 1, in Leigh syndrome and the mitochondrial encephalomyopathies including Kearns-Sayre and MELAS syndromes, and in several other hereditary diseases involving the CNS.