From the Guidelines
For a 16-year-old presenting with a seizure who has a history of seizure disorder, I would order an MRI of the brain as the primary diagnostic study to evaluate the current episode and overall seizure control, as it provides better visualization of structural abnormalities that might be causing seizures, such as cortical dysplasia, mesial temporal sclerosis, or tumors 1. Initially, I would obtain basic laboratory tests including complete blood count, comprehensive metabolic panel (electrolytes, glucose, calcium, magnesium, liver and kidney function), and antiepileptic drug levels if the patient is on medication. An electroencephalogram (EEG) would be essential to assess for epileptiform activity, with consideration for both routine and sleep-deprived EEG to increase sensitivity. If this is a change in seizure pattern or there are concerns about status epilepticus, urgent neuroimaging would be warranted, and a noncontrast CT of the head may be considered in the emergent situation 1. Additionally, if there are signs of infection, I would consider lumbar puncture for cerebrospinal fluid analysis. For adolescents, it's also important to screen for potential triggers such as sleep deprivation, medication non-adherence, alcohol or drug use, and stress. These diagnostic studies help determine whether this seizure represents breakthrough activity in a known disorder, progression of the underlying condition, medication issues, or a new etiology requiring adjustment to the treatment plan. Some key points to consider when ordering an MRI include:
- Using coronal T1-weighted (3 mm) imaging perpendicular to the long axis of the hippocampus
- High-resolution volume (3-D) acquisition (T1-weighted, gradient echo [GRE]) with 1-mm isotropic voxels
- Coronal T2 and coronal and axial (or 3-D) fluid-attenuated inversion recovery sequences to assess for hippocampal signal abnormality, atrophy, and loss of internal structure 1. It is worth noting that the use of intravenous (IV) contrast is not routinely necessary, but it is useful when images without IV contrast are not sufficient or if neoplasm or inflammatory condition is suspected 1.
From the Research
Diagnostic Studies for Seizure Disorder
The following diagnostic studies can be ordered for a 16-year-old presenting with seizure x 1 with a history of a seizure disorder:
- Electroencephalography (EEG) to identify potentially epileptogenic lesions and support the diagnosis of epilepsy 2, 3
- Magnetic Resonance Imaging (MRI) scan to identify structural cerebral pathology that may give rise to seizures 2, 4, 5
- Adjunctive tests such as:
- Ambulatory EEG for patients with infrequent seizures 2
- Video/EEG for patients with frequent seizures or to capture a habitual seizure 2
- Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) to identify focal functional abnormalities 2, 5
- Functional MRI to localize eloquent cortex and tractography to delineate crucial white matter tracts 5
- Brain imaging with MRI at 3T using epilepsy protocols, and reported by expert neuroradiologists who possess the full clinical data 5
- X-ray CT scanning for assessing patients with seizures in the context of an acute neurological illness 5
Specific Considerations
For patients with a history of seizure disorder, it is essential to:
- Use EEG to confirm and classify seizure disorders 3
- Use intracranial EEG with subdural or intraparenchymal electrodes when localization of the seizure focus and mapping of eloquent brain areas are required to plan epilepsy surgery 3
- Consider developmental MRI and image processing to identify subtle abnormalities if no lesion is identified on MRI 5