The EEG is the most useful neurodiagnostic test for distinguishing seizures from nonepileptic paroxysmal disorders and for classifying seizures as having focal or generalized onset. The EEG must be interpreted in the context of the clinical history, because some normal children have focal or epileptiform EEG patterns. Children with seizures may have normal interictal EEGs. When the diagnosis is unclear, more sophisticated EEGs with prolonged recordings and simultaneous video monitoring of the patient in an attempt to capture a typical event may be necessary.
Magnetic resonance imaging (MRI) is superior to computed tomography (CT) in showing most brain pathology,but in the emergency department setting, CT can be performed rapidly and often shows acute intracranial hemorrhage more clearly than MRI. MRI is unnecessary inpatients with the primary generalized epilepsies, such astypical absence and juvenile myoclonic epilepsy. Lesions (tumors, arteriovenous malformations, cysts, strokes, gliosis, focal atrophy) may be identified in 25% of patients,even when the clinical examination and EEG do not suggest focal features. Identification of some lesions, such asfocal cortical dysplasia, hamartoma, and mesial temporalsclerosis, can assist in consideration of surgical treatmentof pharmacoresistant epilepsy.
The decision to institute daily seizure medications for a firstunprovoked seizure is based on the likelihood of recurrencebalanced against the risk of long-term drug therapy. Determination of the recurrence risk is based on the clinical historyand neurodiagnostic testing (Table 181-6). If the recurrencerisk is 75% or greater, it is usually suggested that daily medication be prescribed. Absence seizures, infantile spasms,atypical absence seizures, and atonic seizures are universallyrecurrent at the time of diagnosis, indicating the need fortherapy.
Table 181-6 Recurrence Risk after a First Unprovoked Seizure* SEIZURE TYPE EEG NORMAL, EXAM NORMAL EEG EPILEPTIFORM OR EXAM ABNORMAL BOTH EEG AND EXAM ABNORMAL
Special circumstances: 1.
For absence epilepsy, ethosuximide is the first line treatment.
2.
Adrenocorticotropic hormone, oral corticosteroids, or vigabatrin are used to treat infantile spasms.
Figure 181-1 Treatment for epilepsy.
The goal of treatment is to maintain an optimal functional state. Medication toxicity should be weighed againstthe risk of seizure itself. Initial drug selection is based on themechanism of the seizure (Fig. 181-1). A single agent limitstoxicity, contains cost, and improves compliance. Approximately 60% of children obtain satisfactory seizure controland minimal side effects with the initial drug. If seizurecontrol is not achieved, despite good compliance, additionof a second drug is considered. When available, measuring anticonvulsant blood levels can be helpful in adjustingdosing and monitoring compliance. Levels should be interpreted in light of the patient’s clinical state; a patient with a “low” drug level who is seizure free does not necessarilyneed a higher dose. Anticonvulsant drug levels should bedrawn at trough, usually before the morning doses. When hepatic or renal disease is present, drug binding is likely tobe altered. In this instance, free and bound anticonvulsant levels can be helpful.