Recurrent Encephalopathy During Febrile Illnesses in a 6-Year-Old Boy

Acute onset of encephalopathy is often due to infections or intoxications, but a high index of suspicion should exist for metabolic or autoimmune causes particularly in recurrent cases. A 6-year-old previously healthy Caucasian male presented with confusion and somnolence. He had several days of fever, myalgia, headaches, and rhinorrhea and was influenza-A positive. He was noted to have new urinary incontinence, inability to follow commands, and was responsive only to noxious stimuli. His neurological examination revealed bilateral ankle clonus. Laboratory results were significant for hypoglycemia and high anion gap metabolic acidosis. Cerebrospinal fluid was unremarkable and cultures remained negative. A magnetic resonance imaging (MRI) of the brain showed diffuse gray matter restricted diffusion. His presentation was attributed to acute influenza-A encephalitis. Four months later, he presented with emesis, abdominal pain, dehydration, and hypoglycemia. He subsequently developed dysarthria and confusion. A brain MRI was similar to his previous presentation. A repeat lumbar puncture was normal. A urine organic acid profile showed elevations of ketones and branched chain ketoacids, with mild elevations of N-acetylleucine and N-acetyl isoleucine. This pattern is consistent with maple syrup urine disease (MSUD). Genetic testing revealed that he is a heterozygote for 2 pathogenic variants in the BCKDHB gene (P200X and G278S), confirming MSUD. This case highlights the importance of broadening workup to include inborn errors of metabolism in cases of unexplained encephalopathy. Providers should be aware that diseases such as MSUD can occur in intermittent forms that may not be detected until early childhood.