eMedicine Specialties > Neurology > Seizures and Epilepsy

Temporal Lobe Epilepsy: Differential Diagnoses & Workup

Author: David Y Ko, MD, Associate Professor, Department of Neurology, University of Southern California Keck School of Medicine
Coauthor(s): Soma Sahai-Srivastava, MD, Director of Neurology Ambulatory Care Services, LAC and USC Medical Center; Assistant Professor, Department of Neurology, University of Southern California
Contributor Information and Disclosures

Updated: Apr 8, 2009

Differential Diagnoses

Absence Seizures
Frontal Lobe Epilepsy
Narcolepsy
Periodic Limb Movement Disorder
Tardive Dyskinesia

Other Problems to Be Considered

Panic disorder: This may be associated with autonomic phenomena and anxiety similar to those observed in the simple partial phase of a temporal lobe seizure. However, unlike temporal lobe epilepsy, which lasts seconds to 2 minutes, panic attacks last several minutes (usually longer than 10 minutes).

Occipital lobe epilepsy: This type of epilepsy may propagate to the temporal lobe and be clinically indistinguishable from a temporal lobe seizure (see article Identification of Potential Epilepsy Surgery Candidates).

Excessive daytime somnolence: This may be due to a sleep-related breathing disorder or narcolepsy. It causes episodes of loss of time due to falling asleep frequently.

Psychogenic seizures: Approximately 10-30% of patients with psychogenic seizures also have epileptic seizures.

Frontal lobe epilepsy: Frontal lobe complex partial seizures have certain distinctive characteristics. They appear in clusters of many brief seizures with rapid onset and ending and minimal, if any, postictal state. Prominent features include bizarre behavioral changes including vocalizations and complex motor and sexual automatisms. However, distinguishing frontal lobe complex partial seizures from those of the temporal lobe based solely on clinical features may be difficult; EEG is invaluable for localization.

Absence epilepsy: Generalized absence seizures have an abrupt onset with no aura, usually last less than 30 seconds, and have no postictal state. EEG in absence shows generalized, bilaterally synchronous spike-and-wave discharges and photosensitivity. Complex partial seizures usually are preceded by a distinct aura, last longer than a minute, and have a period of postictal confusion. EEG shows focal spikes in complex partial seizures.

Workup

Imaging Studies

• CT scan of the head is often obtained in the emergency department, but the resolution is quite poor compared with MRI.
• MRI is the neuroimaging modality of choice for patients with temporal lobe epilepsy. Most brain MRI do not include coronal images, but for temporal lobe epilepsy this sequence is more informative than the axial and sagittal cuts.
  • Thin coronal oblique slices of 1.5-2 mm with no gap using spoiled gradient recall images (SPGR) are recommended.
  • All patients with newly diagnosed temporal lobe epilepsy should have a high-resolution MRI with at least a 1.5-Tesla MRI, although the availability of a stronger magnet is increasing resolution.
  • High-resolution MRI shows hippocampal atrophy in many patients with temporal lobe epilepsy by visual analysis alone. Hippocampal atrophy is bilateral in 10-15% of cases. An increase in the T2-weighted signal intensity in the hippocampus may be seen on fluid-attenuated recovery (FLAIR) MRI; this finding is also consistent with hippocampal sclerosis.
• Positron emission tomography with 18-fluorodeoxyglucose (PET-FDG) is a useful tool for interictal seizure localization in surgical candidates when the MRI result is normal.
  • It usually is performed as an adjunctive measure to delineate the epileptogenic zone.
  • Interictal deficits include reduced glucose metabolism in the medial and lateral temporal lobe.
  • Ictal PET recordings are rare.
• Single-photon emission computed tomography (SPECT) is also an adjunctive imaging modality useful only for surgical candidates; the accuracy of seizure localization is about 80-90%.
  • Ictal SPECT done with hexamethylpropyleneamine oxime (HMPAO) shows hyperperfusion in the region of seizure onset. The characteristic pattern is hyperperfusion of the medial and lateral temporal lobe. This requires ictal injection within 30 seconds of seizure onset.
  • Interictal SPECT testing is less sensitive than FDG-PET and ictal SPECT and is not used routinely for localization of the epileptogenic zone.
• Investigational techniques such as MR spectroscopy may become clinically useful in the future in selected surgical candidates with normal MRI.

Other Tests

• EEG should be performed in all patients with suspected temporal lobe epilepsy.
  • Interictal abnormalities, consisting of spike/sharp and slow complexes, usually are located in the anterior temporal region (F7/F8 and T3/T4 electrodes) or basal temporal electrodes (most commonly T1/T2 and in research settings T9/T10 and F9/F10). During video-EEG monitoring sphenoidal electrodes can be useful.
  • One third of patients with temporal lobe epilepsy have bilaterally independent, temporal interictal epileptiform abnormalities.
  • Ictal recordings from patients with typical temporal lobe epilepsy usually exhibit 5-7 Hz, rhythmic, sharp theta activity, maximal in the sphenoidal and the basal temporal electrodes on the side of seizure origin.
  • In documented temporal lobe seizures, lateralized postictal slowing, when present, is a reliable lateralizing finding.
  • A patient with temporal lobe epilepsy can have a normal EEG. The yield of the EEG can be increased on a repeat study with prolonged recordings, and, in certain patients, activation with sleep deprivation can be useful.
  • Video-EEG telemetry is used as part of the presurgical evaluation. It also is used if the diagnosis of temporal lobe epilepsy is suspected but still in question.
  • Intracranial EEG with placement of intracranial subdural electrodes is done only if the patient is a surgical candidate and MRI and other non-invasive EEG data are not sufficiently localizing (see article Presurgical Evaluation of Medically Refractory Epilepsy).
• Another complementary method to assess cerebral physiologic activity similar to EEG is magnetoencephalography (MEG), which measures the magnetic fields generated by the epileptic spikes. The main use of MEG is the co-registration with the MRI to give magnetic source imaging (MSI) in 3-dimensional space.

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