Epileptic and Epileptiform Encephalopathies Workup

Updated: Nov 14, 2017
  • Author: Masanori Takeoka, MD; Chief Editor: Amy Kao, MD  more...
  • Print
Workup

Approach Considerations

Genetic and metabolic testing should be guided by the clinical scenario. No specific testing can be recommended for all cases, given the variability between these disorders. A more aggressive search is usually undertaken when development is slowing, plateauing, or regressing.

Studies to be considered include EEG monitoring, potentially with video to characterize seizures, and magnetic resonance neuroimaging. Every effort should be made to characterize a patient's epilepsy syndrome so that a more focused evaluation may be undertaken.

Next:

Genetic and Metabolic Testing

Testing for specific conditions, particularly treatable ones, should always be performed. Many genetic and metabolic conditions, however, may have similar or nonspecific presentations. Thus, screening metabolic studies may be considered, including the following:

  • Complete blood count
  • Electrolytes, glucose
  • Hepatic enzymes
  • Creatine kinase
  • Lactic acid
  • Pyruvic acid
  • Serum amino acids
  • Urine organic acids
  • Endocrine tests
  • Cerebrospinal fluid evaluation

Screening genetic studies to consider would include karyotype, fragile X testing, and chromosomal microarray analysis. When a specific condition is suspected, testing specific to that condition should be performed because screening studies may be inconclusive, potentially more costly, and less sensitive, depending on the condition suspected. There are targeted epilepsy gene panels that may provide more specific diagnosis when there are specific pathological genetic variants in consideration (e.g., Dravet syndrome; SCN1A and other pathological genetic variants have been associated with this syndrome).

When indicated, consultation with a geneticist may aid in diagnosis.

Previous
Next:

Neuroimaging

In general, neuroimaging is necessary when evidence of focality is noted on either the clinical examination or the EEG. MRI, preferably at least 1.5-Tesla strength, is recommended. CT imaging may be useful in specific cases, such as when calcification may help clarify a diagnosis. [49]

When epilepsy surgery is a consideration, functional neuroimaging studies may be useful. These include single-photon emission computed tomography (SPECT) and positron emission tomography (PET) scans. SPECT measures cerebral blood flow, and PET measures cerebral metabolism.

Magnetoencephalography (MEG) detects the magnetic field of epileptic discharges, which are superimposed on MR imaging. EEG abnormalities from deeper cortical areas such as language cortex may not reach the surface; therefore, the EEG could potentially be unremarkable, whereas MEG can detect the discharges.

Previous
Next:

Electroencephalography

Epileptiform activity may occur only in sleep; therefore, an EEG obtained only in the awake state is considered incomplete. Long-term EEG monitoring (24-h EEG) is considered the best study, but may not be necessary if marked epileptiform activation is seen during sleep, in the routine EEG (eg, electrical status epilepticus of sleep [ESES]). A prolonged EEG may capture a suspicious clinical event, such as a staring spell, and help determine whether it is an actual seizure.

The advantage of quantified EEG (QEEG) with spike localization and steady-state frequency-modulated auditory-evoked response (FMAER) is that spike localization techniques may better map the exact location of the discharge. Steady-state FMAER tests reflect response from the auditory association cortex involved in receptive language function. See the image below.

Epileptic and epileptiform encephalopathies. Frequ Epileptic and epileptiform encephalopathies. Frequency-modulated auditory evoked response (FMAER), before and after treatment with prednisone. The left FMAER is absent. The right FMAER is normal following treatment.

Early infantile epileptic encephalopathy (Ohtahara syndrome)

Interictal EEG reveals a suppression-burst pattern during wakefulness and in sleep. Bursts of generalized high amplitude slowing with admixed multifocal spike discharges are separated by several seconds of diffuse voltage suppression. Ictal EEG reveals typical generalized electro-decrements during tonic seizures. [50]

Early myoclonic encephalopathy

The interictal EEG reveals a burst-suppression pattern more pronounced in sleep, with longer periods of diffuse voltage suppression lasting up to 10 seconds. [34] The EEG may evolve to hypsarrhythmia or multifocal spike discharges and may then return to a suppression-burst pattern afterwards.

Infantile spasms (West syndrome)

Hypsarrhythmia, the typical interictal EEG finding, consists of a disorganized pattern with asynchronous, very-high-amplitude slowing and frequent multifocal spike and sharp wave discharges. The ictal EEG typically reveals a generalized slow wave followed by diffuse voltage attenuation (electro-decrement), which may associated with a spasm or be only electrographic (without clinical correlate).

Malignant epilepsy with migrating partial seizures in infancy

The interictal EEG reveals multifocal epileptiform activity and slowing. The ictal EEG confirms multifocal onsets, which may shift from seizure to seizure.

Severe myoclonic epilepsy of infancy (Dravet syndrome)

The interictal EEG is initially normal and then deteriorates to a nonspecific pattern of multifocal epileptiform discharges and multifocal or generalized slowing. A photoparoxysmal response may occur early in childhood. Ictal EEG findings depend on the seizure type. The ictal focus may shift during some seizures.

Myoclonic status in nonprogressive encephalopathies

The interictal EEG consists of multifocal epileptiform discharges and background slowing. Epileptiform discharges are potentiated in sleep, in some cases similar to an ESES pattern. Ictal EEG recording may demonstrate generalized slow spike and wave, or an absence pattern, depending on the seizure type.

Myoclonic-astatic epilepsy (Doose syndrome)

The EEG is initially normal or mildly abnormal, with worsening. Generalized spike and poly-spike wave discharges and excessive theta activity in the central-parietal regions typically develop interictally. Myoclonic seizures demonstrate generalized spike or poly-spike wave discharges, and atonic seizures demonstrate poly-spike wave discharges with electromyogram (EMG) silence.

Lennox-Gastaut syndrome (LGS)

The hallmark interictal EEG finding is generalized slow spike-wave discharges (usually 1.5-2 Hz), often with multifocal epileptiform discharges. Bursts of generalized fast spike discharges (approximately 10 Hz) are common in sleep (see the image below).

Ictal EEG findings depend on the seizure type captured. Tonic seizures demonstrate a diffuse electrodecrement pattern with superimposed low amplitude, fast spike discharges. A slow spike-wave pattern may be seen with atypical absences, and myoclonic seizures may have a diffuse spike or poly-spike wave pattern.

Epileptic and epileptiform encephalopathies. EEG s Epileptic and epileptiform encephalopathies. EEG showing an epileptiform beta frequency burst.

Landau-Kleffner syndrome and epilepsy with continuous spikes-waves during slow sleep

The hallmark EEG finding of Landau-Kleffner syndrome (LKS) and continuous spikes-waves during slow sleep (CSWS) is ESES, consisting of near-continuous, diffuse, epileptiform discharges in non-REM sleep (see the first image below). Often, multifocal and frequent epileptiform activity may also be present (see the second image below).

EEG of a patient with Landau-Kleffner syndrome sho EEG of a patient with Landau-Kleffner syndrome showing electrical status epilepticus of sleep (ESES).
Epileptic and epileptiform encephalopathies. Wakin Epileptic and epileptiform encephalopathies. Waking EEG in Landau-Kleffner syndrome, showing left posterior spikes.

These discharges are markedly sleep potentiated; however, epileptiform activity is often present during rapid eye movement (REM) sleep and waking as well. ESES was initially described as having an EEG spike wave quantity occupying 85% of non-REM sleep; this is not an absolute requirement, however, as fewer discharges (perhaps 50% spike wave index of sleep) may result in cognitive deficits. [51, 52, 53]

The term ESES is somewhat misleading, since the pattern is not a clear ictal pattern. However, it is believed to cause more impairment than interictal activity in other disorders, thus representing a gray zone between the ictal and interictal states. Ictal EEG findings depend upon the seizure type recorded.

In LKS, the ESES discharges tend to be more posteriorly predominant (temporal or temporal-occipital), whereas in CSWS, frontotemporal or centrotemporal discharges are more common. In CSWS, frontotemporal discharges result in more executive function impairment and autistic behaviors, while a more central EEG focus (posterior frontal lobe involvement) may result in more motor impairment, including dyspraxia, dystonia, and ataxia.

As in LKS, the frequent epileptiform discharges contribute to the cognitive impairments seen. The ictal EEG pattern depends upon the seizure type captured.

Benign focal epilepsy of childhood with centro-temporal spike discharges (benign rolandic epilepsy)

The interictal EEG pattern is characterized by frequent, sleep-potentiated, bilateral or unilateral, centrotemporal, sharp or spike-wave discharges. The EEG pattern may be seen in the absence of clinical seizures and is then termed the benign rolandic epilepsy (BRE) trait.

For more information, see Epileptiform Normal Variants on EEG, Generalized Epilepsies on EEG, Localization-RelatedEpilepsies on EEG, EEG in Common Epilepsy Syndromes, and EEG in Status Epilepticus.

Previous
Next:

Neuropsychological Examination

Preservation of nonverbal skills is an important diagnostic feature of LKS and may help differentiate LKS from other disorders, including autism.

Previous