Frontal Lobe Epilepsy Workup

Updated: Dec 30, 2015
  • Author: Sheryl Haut, MD; Chief Editor: Selim R Benbadis, MD  more...
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Workup

Approach Considerations

Blood testing

Blood tests should be performed to rule out a metabolic cause of new-onset seizures, eg, hypoglycemia or hypomagnesemia. Once the diagnosis of epilepsy is established, blood testing remains important in the management of patients who are taking anticonvulsants. Blood monitoring should be guided by the likely complications of a given anticonvulsant and, more importantly, by patient risk factors and symptoms. Blood tests include the following:

  • Complete blood count (CBC) - Monitor for neutropenia and thrombocytopenia
  • Liver function tests
  • Anticonvulsant levels

With regard to the third item above, most anticonvulsants have a typical therapeutic window, although these levels should be used only as a guide. levels are less frequently monitored for the newer anticonvulsant agents.

Magnetic resonance imaging

The imaging modality of choice in patients with frontal lobe seizures is MRI. Recent advances in MRI have improved the identification of underlying lesions, which are reported to be present in up to 50% of patients with frontal lobe epilepsy.

Optimally, MRI with gadolinium should be obtained with high resolution, 1 mm thick slices, and multiple sequences. If EEG or other testing indicates a potential epileptogenic zone, thin slices through the area of interest should be requested. A field strength of 3 Tesla (3T) can further increase the identification of lesions. [10]

Positron emission tomography scanning

PET scanning is being increasingly used in the presurgical evaluation of patients with extratemporal epilepsy.

Interictal hypometabolism, reflective of focal dysfunction, may be seen in areas that were normal on MRI, although this finding is better established for temporal than for frontal lobe epilepsy. The role of tracer-imaging functions other than glucose metabolism, such as benzodiazepine receptors, still is being defined.

Decreased thalamic metabolism ipsilateral to the seizure focus may be seen in nonlesional frontal lobe epilepsy, particularly in association with a long duration of intractability.

Single-photon emission computed tomography

Ictal single-photon emission computed tomography (SPECT) scans may be obtained during prolonged video-EEG monitoring.

Hyperperfusion seen on ictal SPECT scanning is suggestive of an area of seizure onset. The sensitivity of ictal SPECT scan hyperperfusion is reported to be higher in frontal lobe epilepsy than in temporal lobe epilepsy.

As seizures in patients with frontal lobe epilepsy are often brief and may generalize rapidly, obtaining an ictal SPECT scan is difficult.

Magnetic resonance spectroscopy

Magnetic resonance spectroscopy (MRS), while still mainly an experimental testing modality, is being increasingly used in the presurgical evaluation of intractable epilepsy.

MRS may demonstrate decreased NA/Cr ratios in the frontal epileptogenic zone, consistent with abnormalities of energy metabolism.

Electroencephalography

All patients with frontal lobe epilepsy should undergo EEG evaluation. Patients with intractable epilepsy, or in whom the diagnosis is doubtful, should undergo prolonged video-EEG monitoring. If the events are primarily or exclusively nocturnal, polysomnography should be considered, with extended EEG montages if available. Electroencephalography is discussed further in the subsections below.

Histologic findings

Tissue from surgical resections for intractable frontal lobe epilepsy may demonstrate evidence of a developmental lesion, tumor, gliosis, or vascular malformation.

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Scalp EEG and Prolonged Video-EEG Monitoring

Interictal EEG

Findings in interictal EEGs may be normal. Spikes or sharp waves may be absent; may appear maximal unilaterally, bilaterally, or in the midline; or may appear generalized due to secondary bilateral synchrony.

Background rhythm abnormalities, with or without focal slowing, may be present.

Ictal EEG

Closely spaced frontal electrodes can enhance localization in ictal EEGs.

Ictal onset often is seen poorly from the scalp and is highly variable in appearance. EEGs can also be affected by muscle artifact, which may obscure the findings.

Lack of ictal discharge in the temporal lobes suggests a frontal onset.

Video analysis of seizure semiology may suggest frontal epilepsy. Fencing posturing and lack of postictal confusion are highly suggestive. [4]

Clinical semiology can provide lateralization information, with many unilateral movements or postures predicting a contralateral seizure onset. [11]

Postictal EEG

Postictal slowing also can be confirmatory, and at times, localizing or lateralizing.

Go to EEG Video Monitoring for complete information on this topic.

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Intracranial EEG

Patients with suspected frontal lobe epilepsy frequently require invasive EEG monitoring. Intracranial EEG is used for localizing the epileptogenic region and for functional mapping prior to resection. Electrode coverage of frontal and temporal (and/or parietal) lobes may be needed.

Stereotactically placed depth electrodes have the greatest accuracy if the area of interest is well defined, but records from a small anatomic area.

Subdural strips and grids have less hemorrhagic risk, sample more broadly, and can be used to perform cortical mapping, but they have higher infection risk and less anatomic specificity. Epidural pegs and screws are used less often than either depth or subdural electrodes.

Ictal onset most often appears as a low-voltage, high-frequency discharge (ie, buzz), although rhythmic activity at alpha, theta, or delta frequencies may be seen. Because of rapid bilateral synchrony, discharge on scalp recording may appear bilateral.

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