What is the diagnosis and recommended treatment for a patient with an abnormal 48-hour ambulatory EEG showing focal epilepsy arising from the left temporal region?

Focal Epilepsy Arising from Left Temporal Region: Diagnosis and Treatment

This patient has confirmed focal epilepsy with a left temporal seizure onset zone demonstrated by ambulatory EEG, and should be initiated on antiepileptic medication with levetiracetam, carbamazepine, or lamotrigine as first-line monotherapy, with consideration for surgical evaluation if seizures prove medication-resistant after trial of two appropriate antiepileptic drugs. 1, 2

Diagnostic Interpretation

The EEG findings definitively establish focal epilepsy:

• Seizure onset zone confirmed: The electrographic seizure originated from the left temporal region (T3>F7, T5) with characteristic low amplitude rhythmic theta activity that built up in frequency and evolved over the left parasagittal region 3, 4

• Prolonged electrographic seizure: The 8-minute duration seizure with minimal clinical manifestations represents a focal impaired awareness seizure, typical of temporal lobe epilepsy 5, 6

• Aura characteristics: The patient's reported "floating feeling" and bilateral head heaviness 15 minutes before ictal EEG changes likely represents a subjective aura originating from the temporal focus, though no EEG correlate was captured at that time 5, 6

• Absence of interictal epileptiform discharges: While no interictal spikes were seen, this does not exclude focal epilepsy—the ictal recording provides definitive localization 7

Additional Diagnostic Workup Required

High-resolution MRI with epilepsy protocol is mandatory to identify structural lesions:

• Obtain thin coronal slices through the temporal lobes with T1-weighted imaging, high-resolution volume T1-weighted gradient echo, and coronal T2 and FLAIR sequences 3, 4, 5

• MRI sensitivity for temporal lobe pathology is 84%, significantly higher than CT at 62% 3, 4

• Look specifically for mesial temporal sclerosis, focal cortical dysplasia, tumors (especially low-grade epilepsy-associated brain tumors), or temporal encephaloceles 8, 9

If MRI is negative or shows nonspecific findings, obtain FDG-PET:

• PET demonstrates glucose hypometabolism in the epileptogenic zone with 79-95% sensitivity and specificity 5

• PET sensitivity for temporal lobe epilepsy is 63-67% and can identify subtle lesions missed on MRI 3, 4, 5

• Hypometabolism often extends beyond the seizure onset zone, reflecting broader cerebral dysfunction 5

Consider ictal SPECT or SISCOM if surgical evaluation proceeds:

• Ictal SPECT shows hyperperfusion of the epileptogenic region during seizures 3, 4

• SISCOM (subtraction ictal SPECT co-registered to MRI) improves sensitivity and specificity, with >90% localization sensitivity in temporal lobe seizures 8, 3, 4

• Concordance between MRI, EEG, PET, and ictal SPECT predicts better surgical outcomes 8, 3, 4

Medical Management Algorithm

Initiate antiepileptic drug monotherapy immediately:

• First-line options: Levetiracetam (1000-3000 mg/day in divided doses), carbamazepine, lamotrigine, or oxcarbazepine are appropriate initial choices for focal-onset seizures 1, 2

• Levetiracetam demonstrated 26-30% reduction in seizure frequency over placebo in focal epilepsy trials, with responder rates (≥50% reduction) of 37-42% 1

• Consider patient-specific factors: adverse effect profiles, age, pregnancy potential, and concomitant medications when selecting initial therapy 2

Define medication resistance:

• Patient is considered drug-resistant if seizures persist after adequate trials of two appropriate antiepileptic drugs 8

• Approximately 30% of focal epilepsy patients do not respond to two antiepileptic medications 8

Timeline for surgical consideration:

• Standard practice allows approximately 2 years of medical management before considering surgery, though earlier intervention may be appropriate when multiple appropriate drugs fail 3, 4

• Earlier surgical referral should be considered given the clear focal onset and potential for complete resection 3, 4

Surgical Evaluation Pathway

If medication-resistant, refer for comprehensive epilepsy surgery evaluation:

• Complete surgical resection of the epileptogenic region is the treatment of choice for medically refractory temporal lobe epilepsy, with approximately 65% of patients becoming seizure-free 8, 3, 4

• Extended temporal resection shows higher success rates than lesionectomy alone 3, 4

• Temporal lobectomy demonstrates superior seizure outcomes compared to lesionectomy in multiple studies 3, 4

Critical prognostic factors for surgical success:

• Concordance between multiple diagnostic modalities (MRI, EEG, PET, SPECT) strongly predicts favorable outcomes 8, 3, 4, 5

• Complete removal of the epileptogenic zone is essential for optimal seizure control 3, 4

• Incomplete resection significantly increases seizure recurrence risk 3, 4

• Duration of epilepsy prior to surgery does not significantly affect outcome 3, 4

Important Clinical Caveats

Beware of these pitfalls:

• The 15-minute delay between reported aura and EEG changes suggests the aura may represent early seizure activity below scalp EEG detection threshold—this does not invalidate the temporal localization 7

• Absence of dramatic heart rate changes during the seizure is typical for temporal lobe seizures and does not suggest non-epileptic events 6

• The irregular sinus rhythm noted on single-lead ECG requires cardiology evaluation independent of epilepsy management 8

• Bitemporal or extratemporal hypometabolism on PET may indicate higher risk of postoperative memory decline and should prompt neuropsychological evaluation before surgery 3, 5

Lateralizing features to document:

• Postictal aphasia would strongly lateralize to left temporal onset (language-dominant hemisphere) 6

• Contralateral focal jerking or tonic head deviation would support left temporal localization 6

• Well-formed ictal speech would suggest right temporal onset, making left temporal localization more certain in its absence 6

Functional imaging interpretation:

• Temporal lobe hypometabolic regions on PET typically extend beyond the epileptogenic zone 5

• Cognitive impairment correlates with extratemporal hypometabolism involving mesial frontoparietal networks 3, 5

• Contralateral thalamic hypometabolism predicts poorer surgical outcomes compared to ipsilateral thalamic involvement 3