急性脑病起病的晚发枫糖尿症

枫糖尿症（maple syrup urine disease，MSUD）是一种较常见的氨基酸代谢障碍性疾病。患者通常在新生儿期至婴幼儿期发病，学龄期以急性脑病起病的病例未见报道。本文报道1例MSUD患儿，8岁6个月首次发病，以感染后急性脑病症状为主要临床表现，于发病第2天时来院，一般化验发现代谢性酸中毒、血尿酸增高、脑脊液蛋白质降低，头颅磁共振扫描显示双侧小脑齿状核、脑干、双侧丘脑、壳核、尾状核及双侧大脑半球皮层呈现长T1，长T2信号，头颅弥散频谱（DWI）示以上部位呈明显高信号。血代谢检查示：血亮氨酸/异亮氨酸、缬氨酸显著高于正常范围；尿液代谢结果示：2-羟基异戊酸、2-羟基丁酸、2-酮异戊酸和2-酮异己酸亦显著增高，提示MSUD。同时游离肉碱明显降低，提示继发性肉碱缺乏、酮症。经控制氨基酸摄入，予大剂量维生素B1、葡萄糖、左旋肉碱静脉点滴，入院后第5天病情明显好转，第7天病情完全恢复，未遗留任何中枢神经系统后遗症。根据患儿治疗效果考虑为硫胺有效型。继续给予维生素B1口服，控制蛋白质饮食（每日1 g/kg）治疗1个半月后复查，血、尿代谢结果完全正常，复查头颅MRI结果明显改善。对以急性脑病起病的病例，要警惕遗传代谢性疾病的可能。如能及时诊断、正确治疗，可以有效地预防中枢神经系统后遗症的发生，改善预后。

Acute encephalopathy due to late-onset maple syrup urine disease in a school boy

Maple syrup urine disease is a common amino acids metabolic disease. In most patients, onset occurs in the neonatal period and infancy. In this study, the case of a school boy with acute encephalopathy due to late-onset maple syrup urine disease is summarized. The boy (8.5 years) was admitted because of acute encephalopathy after suffering from infection for two days at the age of eight and a half years. Metabolic acidosis, hyperuricemia and decreased protein level in cerebrospinal fluid were found by general laboratory tests. Magnetic resonance imaging of the brain revealed signal intensity abnormalities in the bilateral cerebellum dentate nucleus, brainstem, thalamus, putamen, caudate nucleus and cortex of the cerebral hemispheres. On T1WI and T2WI scanning, hyperintensive signal was found. Blood leucine and valine were significantly elevated. Urinary 2-hydroxy isovaleric acid, 3-hydroxybutyric acid, 2-keto isovaleric acid, and 2-keto acid also increased. Both the blood amino acid and urine organic acid profiles led to the diagnosis of maple syrup urine disease. In the acute period, the patient was treated with a large dose of vitamin B1, glucose, L-carnitine and a protein-restrict diet. The patient's condition improved significantly after five days of treatment, and he recovered completely two days later. Afterwards, treatment with vitamin B1, L-carnitine and a protein-restrict diet (1 g/kg/day) was continued. One and a half months later, blood amino acids and urine organic acids returned to normal. Magnetic resonance imaging of the brain also indicated a great improvement. It was concluded that inborn metabolic disease should be considered in the patients with an onset similar to acute encephalopathy. Early diagnosis and proper treatment can prevent brain damage and improve prognosis.