Unilateral cerebral injury mimicking hemiconvulsion-hemiplegia-epilepsy syndrome in a boy with newly diagnosed infantile-onset ornithine transcarbamylase deficiency: A case report and literature review

Background Ornithine transcarbamylase deficiency, the most common urea cycle disorder, typically presents with neurological symptoms caused by hyperammonemia. Although brain injuries are typically diffuse, unilateral lesions have been reported. Hemiconvulsion–hemiplegia–epilepsy syndrome is a neurological disorder occurring in infancy or early childhood, characterized by prolonged unilateral seizures, subsequent cerebral hemiatrophy, and epilepsy. These conditions may have overlapping clinical features. Case A 4-month-old boy presented with fever and asymmetric seizures during an adenovirus infection. Blood tests revealed hyperammonemia, elevated liver enzyme levels, coagulopathy, and lactic acidosis. Brain MRI showed diffuse cortical edema in the left hemisphere with abnormal EEG discharges. Hemiconvulsion–hemiplegia–epilepsy syndrome was provisionally suspected, and steroid pulse therapy and supportive treatment were initiated. Due to fluctuating blood ammonia levels, arginine was administered. Further metabolic evaluation demonstrated increased urinary orotic acid excretion, low plasma citrulline and arginine levels, and elevated plasma glutamine. A family history of neonatal-onset disease supported the clinical diagnosis. The patient was treated with a protein-restricted diet, citrulline, arginine, and sodium phenylbutyrate. At 1 year and 2 months of age, he showed mild right upper limb weakness without epilepsy. A review of the literature identified seven cases of urea cycle disorders with unilateral brain lesions, six involving ornithine transcarbamylase deficiency. Conclusion In ornithine transcarbamylase deficiency, acute infection may trigger unilateral cerebral injury, mimicking the hemiconvulsion–hemiplegia–epilepsy syndrome. Early metabolic intervention may help mitigate hyperammonemia and reduce the risk of neurological injury, highlighting the importance of considering metabolic disorders in infants with unilateral brain injury.