Laboratory Studies

Basic Metabolic Panel

Seizures provoked by metabolic abnormalities in an otherwise normal child are rare. Therefore, basic tests should be done based on clinical judgment per American Academy of Neurology (AAN) guidelines for evaluation of first unprovoked seizure (3).

Lumbar Puncture

If there is clinical suspicion of meningitis or encephalitis, lumbar puncture should be done per AAN guidelines for evaluation of first unprovoked seizure.

Urine Toxicology

Routine urinalysis is not recommended, but if there is clinical suspicion of recreational drug use, a urine drug screen should be obtained.

Liver Function Tests

If there is history suggestive of a potentially degenerative, metabolic or storage disorders or there is anticipation of starting antiepilepsy drugs (AEDs), liver function tests should be performed.

Screening for Inherited Metabolic Disorders

These tests may not be obtained during the initial evaluation, but are very important in seizure evaluation and management and so are mentioned here.

About 200 inherited disorders are associated with seizures (34). There are clues such as certain seizure types, characteristic EEG patterns, and specific epilepsy syndromes that point to some of these disorders. Associated symptoms of mental retardation, developmental delays, hypotonia, macrocephaly and microcephaly, and failure to thrive may also suggest the possibility of a metabolic disorder. In patients with myoclonic seizures, spasms, early-onset tonic seizures, and infantile-onset hypomotor and versive seizures, inherited metabolic disorders should be suspected (34). Other characteristics of seizures associated with inherited disorders include onset in the first month of life, usually partial seizures with migrant nature and successive appearance (35). West syndrome, early myoclonic encephalopathy, and Ohtahara syndrome are known to be associated with metabolic disorders (see Table 11-1).

EEGs showing burst suppression, hypsarhythmia, and diffuse severe depression without obvious cause demand evaluation for inherited disorders (see Table 11-2).

Serum amino acids and urine organic acids can be used as an initial screen in patients with the previously mentioned seizure types and syndromes. Cerebrospinal fluid (CSF) glucose, lactate, and amino acids are recommended for infantile seizures without clear etiology. It is important to obtain samples during the presentation of symptoms before treatment because otherwise samples may be falsely normal or difficult to interpret (36) (see Tables 11-3 and 11-4) (35-37).

Disorders of carnitine and fatty acid oxidation acutely present with a history of decreased oral intake followed by increasing lethargy, obtundation or coma, and seizures. Other features include history of recurrent hypoglycemic, hypoketotic encephalopathy, potential developmental delay, progressive lipid storage myopathy, table 11-1 Epileptic Syndromes and Inborn Errors of Metabolism

Neonatal Seizures (ILAE 3.1)

Urea cycle defects: argininosuccinic acidemia, ornithine transcarbamylase, carbamylophosphate synthetase Organic acidurias: maple syrup urine disease Disorders of biotin metabolism: early-onset multiple carboxylase deficiency (holocarboxylase synthatase deficiency)

Peroxisomal disorders: Zellweger syndrome, acyl-CoA

oxidase deficiency Other: molybdenum cofactor deficiency/sulfite oxidase deficiency, disorders of fructose metabolism, pyridoxine dependency

Early Myeloclonic Encephalopathy/Early Infantile Epileptic Encephalopathy (ILAE 2.3.1)

Nonketotic hyperglycinemia Propionic acidemia D-Glyceric academia Leigh disease

Cryptogenic Myeloclonic Epilepsies (ILAE 2.2) Other Than Infantile Spasms or Lennox-Gestaut Syndrome

GM1 gangliosidosis

GM2 gangliosidosis

Infantile neuroaxonal dystrophy

Neuronal ceroid lipofuscinosis

Glucose transporter defect 1 deficiency

Late-onset multiple carboxylase deficiency

Disorders of folate metabolism, methylenetetrahydrofo late reductase deficiency Arginase deficiency (urea cycle defect) Tetrahydrobiopterin deficiency (aminoaciduria) Tyrosinemia type I

West Syndrome, Generalized 2.2

Phenylketonuria/hyperphenylalaninemia Pyruvate dehydrogenase deficiency Pyruvate carboxylase deficiency

Carbohydrate-deficient glycoprotein syndrome (type III) Organic acidurias Amino acidurias

Abbreviations: ILAE, International League Against Epilepsy; CoA, coenzyme A. Source: Nordli and De Vivo 2002 (34).

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