Systemic Primary Carnitine Deficiency Presenting With Substantia Nigra and Basal Ganglia Injury: A Case Report

Systemic primary carnitine deficiency (SPCD) is a rare congenital fatty acid metabolism disorder causing impaired β-oxidation and energy production, leading to hypoglycemia, metabolic encephalopathy, and sudden death. Early diagnosis and treatment, including L-carnitine supplementation and fasting avoidance, can improve prognosis. However, newborn screening (NBS) criteria differ by region, and standardized guidelines are lacking. This report presents a case of SPCD undetected by NBS, resulting in basal ganglia damage and dystonia due to metabolic decompensation. A 1-year-9-month-old girl with no abnormalities on NBS presented with impaired consciousness. She exhibited hypoketotic hypoglycemia, hyperammonemia, and myocardial hypertrophy. Suspecting a fatty acid metabolism disorder, L-carnitine and high-calorie infusion were initiated. Laboratory tests revealed markedly low serum total and free carnitine levels, and genetic analysis confirmed a homozygous <i>SLC22A5</i> mutation. Brain MRI on day 7 revealed bilateral basal ganglia and substantia nigra abnormalities. The patient developed severe dystonia and respiratory failure, requiring ECMO management. L-DOPA was initiated on day 62, resulting in improvements in dystonia, swallowing, and motor function. By day 88, MRI showed resolution of basal ganglia abnormalities, though cerebral atrophy persisted. Basal ganglia damage is a rare but severe SPCD complication. L-DOPA may alleviate dystonia by acting on dopaminergic neurons in the substantia nigra. Early ketone measurement during emergencies is crucial for diagnosing fatty acid metabolism disorders. A standardized NBS protocol with a defined carnitine cutoff value is essential for early detection and prevention of SPCD complications.