Investigations
1st investigations to order
EEG
Test
Order in the initial assessment of all patients; a sleep-deprived routine EEG including awake and asleep. Hyperventilation is essential.
The EEG may be repeated to assess treatment response in childhood absence epilepsy (CAE). There is some suggestion that normalisation of EEG correlates with greater likelihood of resolution of CAE. Patients with longer seizures at baseline may have more favourable initial treatment response, but are at greater risk for inattention.[38]
Result
generalised 3 Hz spike-and-wave in typical absence; generalised 1.5 to 2.5 Hz spike-and-wave in atypical absence; generalised 4 to 6 Hz spike-and-wave in juvenile myoclonic epilepsy (JME)
Investigations to consider
MRI brain
Test
Required only in settings where the history, clinical course, physical examination, or EEG findings do not fit with typical absence seizures or generalised epilepsy syndromes or if clinical course is not typical (e.g., a patient with suspected CAE has not responded to first 2 treatment modalities).
Result
usually normal in childhood absence epilepsy (CAE); variety of findings ranging from focal encephalomalacia or cortical dysplasia to diffuse cortical malformations may be found in epilepsies such as Lennox-Gastaut
testing for metabolic disorders (e.g., serum amino acids, urine organic acids, lactate pyruvate or specific enzymatic tests)
Test
Metabolic tests are generally indicated when the clinical and EEG findings do not fit with typical absence seizures or an epilepsy syndrome but suggest a symptomatic aetiology. There is a broad variety of metabolic tests that can be performed and these need to be tailored to the individual. Possible metabolic disorders causing atypical absence seizures include aminoacidurias, organic acidurias, mitochondrial disorders, and lysosomal storage diseases.[39]
Result
variable, depending on specific test
cerebrospinal fluid and serum glucose
Test
Consider if the patient has typical absence seizures that began before 4 years of age.
May also be indicated in patients with refractory absence seizures.
Result
cerebrospinal fluid glucose low; serum glucose normal
Emerging tests
gene testing
Test
In rare instances with a characteristic family history of other generalised epilepsies (generalised epilepsy with febrile seizures plus [GEFS+]), commercial testing for SCNA gene mutations may be indicated. As more genes are identified for these syndromes, this may become more common. For patients under age 4 years or with intractable absence epilepsy, genetic testing of the SLC2A1 gene for GLUT1 deficiency should be considered.[29][33][34] For epilepsies involving atypical absence seizures, karyotype and more detailed chromosomal analysis may be indicated.
Result
may be positive
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