Approach Considerations
Lumbar puncture should be performed in all cases of suspected meningitis, unless neuroimaging or funduscopic examination suggests increased intracranial pressure.
Brain biopsy is strongly suggested to confirm the diagnosis in suspected cases of Rasmussen encephalitis, or in focal progressive lesions of unknown etiology.
Lab Studies
The following blood studies can be useful for excluding other disorders:
- Electrolytes, including serum glucose
- Thyroid-stimulating hormone and/or thyroid profile
- Toxin and drug screen
Electroencephalography
An electroencephalogram (EEG) fortuitously obtained during the patient's symptoms can provide clear support for a diagnosis. EEGs obtained soon after a suspected seizure often record nonspecific patterns or may be normal.
Activation by sleep deprivation, photic stimulation, and/or hyperventilation increases the ability to detect abnormalities on a single recording. Repeat or prolonged recording may increase the chance of recording interictal or ictal patterns of diagnostic significance.
Although interictal spikes in an appropriate anatomical location for the symptoms of the suspected seizure are highly suggestive of epilepsy, EEG abnormalities may be distant in location from the actual area of seizure onset, giving poor localizing information for possible epilepsy surgery. EEG performed with extra scalp electrodes or intracranial electrodes is necessary if involvement of mesial structures is suspected.
Single or rare interictal sharp waves may be normal variants, and further diagnostic confirmation should be pursued. Normal EEG findings do not exclude the possibility of epilepsy.
Video-electroencephalography
EEG-video monitoring is often necessary to record typical clinical events and to correlate them with any electrographic changes. Many SPS are characterized by EEG patterns that are difficult to record, and the diagnosis may depend entirely on video analysis of reproducible ictal semiology of multiple events, or on observation by trained personnel.
Electrocardiographic Studies
Routine 12-lead ECG and a rhythm strip should be obtained in all subjects with cardiac, thoracic, gastrointestinal, or focal positive and negative sensations. Twenty-four–hour Holter monitoring and inpatient telemetry are appropriate if daily episodes are expected (based on history). A telephone transmittal cardiac recorder can be useful for episodes occurring infrequently.
Imaging Studies
CT scan of the brain, with and without contrast, is primarily useful and appropriate in an emergency setting or for patients unable to have MRI studies. Coronal T2-weighted MRI with fluid-attenuated inversion recovery (FLAIR) and careful attention to the mesial temporal structures is more likely to demonstrate abnormalities if a diagnosis of SPS already has been established.
Low-resolution MRI, under 1.5 T, should be discouraged in any evaluation of epilepsy. This typically makes the use of "open MRI" inadequate.
Histologic Findings
Various microscopic abnormalities, including the following, can be found in the epileptogenic zone:
- Focal cortical dysplasia
- Hippocampal sclerosis
- Neoplasia
- Cortical inflammation
- Encephalomalacia
- Vascular malformation
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