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Seizures are one of the most frequently occurring neurologic phenomena in childhood; an inborn error of metabolism should always be considered in the diagnostic workup of patients with seizures after more common causes have been excluded. Many of the known inborn metabolic errors associated with seizures can be detected by metabolite measurement in urine or blood. It is now recognized, however, that there are several conditions in which peripheral metabolite profiles remain normal. Abnormal metabolism is indicated only by the accumulation or absence of specific metabolites within the central nervous system. Some of these disorders can be detected by in vivo magnetic resonance spectroscopy. More often, an etiology can be ascertained only by analysis of specific metabolites in cerebrospinal fluid. This review describes the utility of cerebrospinal fluid metabolite analysis in the differential diagnosis of inborn errors of metabolism that lead to infantile epilepsy. These include disorders of central nervous system energy metabolism, creatine synthesis and transport, serine biosynthesis, and glucose transport, together with defects affecting the gamma-aminobutyric acid (GABA), catecholamine, and serotonin neurotransmitter systems. In addition, information is provided regarding detection of an early-onset seizure disorder that responds to folinic acid.

We have analyzed changes in cerebrospinal fluid (CSF) concentrations of monoamine-related substances to clarify the mechanism of the antiepileptic action of thyrotropin-releasing hormone (TRH). TRH-tartrate was administered to 14 patients with intractable epilepsy. Before and 2 weeks after TRH administration, CSF was collected and analyzed for tryptophan and tyrosine metabolites. Among monoamine-related substances, only CSF concentrations of kynurenine were increased after TRH therapy. Considering the fact that kynurenic acid acts as antagonist on the NMDA receptor complex, the results of this study may explain at least one of the mechanisms of the effectiveness of TRH therapy for intractable epilepsy.

The neuropharmacologic basis of infantile spasms and the mechanism by which adrenocorticotropic hormone (ACTH) exerts its therapeutic effects are unknown. This is a critical review of cerebrospinal fluid neurotransmitters or their metabolites in infantile spasms before and during treatment with ACTH, and of clinical drug trials with drugs acting on neurotransmission. Cerebrospinal fluid studies have shown lower gamma-aminobutyric acid (GABA), ACTH, and 5-hydroxyindoleacetic acid concentrations in patients with infantile spasms compared to controls, elevated lysine and glutamate, variable or no differences in homovanillic acid, 3-methoxy-4-hydroxyphenylglycol, norepinephrine, corticotropin-releasing hormone, and beta-endorphin. Chronic treatment with ACTH in infantile spasms reduces cerebrospinal fluid GABA, beta-endorphin, and somatostatin, increases norepinephrine and tyrosine, and has variable or no effect on homovanillic acid, 3-methoxy-4-hydroxyphenylglycol, 5-hydroxyindoleacetic acid, histamine, and tryptophan. Small therapeutic trials with drugs that act through different neurotransmitters such as methysergide, alpha-methylparatyrosine, various benzodiazepine agonists, and vigabatrin lend some support to a role for GABA and monoamines in infantile spasms. These data, though promising, provide only a hint of potential neurotransmitter disturbances, and more basic and clinical data are needed.