Temporal Lobe Epilepsy

Temporal lobe epilepsy is a focal epilepsy arising from the mesial or lateral temporal lobe. Mesial temporal epilepsy with hippocampal sclerosis is the commonest drug resistant focal epilepsy.

It accounts for about 30 to 40% of focal epilepsy. Onset is usually in childhood or adolescence, and about one third of patients are resistant to drugs.

Causes. Hippocampal sclerosis (often following prolonged febrile seizures in childhood), tumours, cortical dysplasia, vascular malformations, infection, trauma and autoimmune encephalitis.

Seizure types. Focal aware seizures (auras), focal impaired awareness seizures and focal to bilateral tonic clonic seizures.

Course. Seizure freedom with drugs is achieved in about 50 to 60%. Cognitive (memory), mood and psychiatric complications are common, and sudden unexpected death in epilepsy risk rises with uncontrolled seizures.

Pathophysiology.

Neuronal loss and gliosis in the hippocampus, with mossy fibre sprouting and disinhibition, create a hyperexcitable network that spreads through limbic circuits.

Recurrent seizures further damage hippocampal structures, impairing memory.

• Auras: rising epigastric sensation, déjà vu, fear, olfactory or gustatory hallucinations.
• Focal impaired awareness: staring, oroalimentary automatisms (lip smacking, chewing), hand automatisms, dystonic posturing of the contralateral arm, lasting 1 to 3 minutes.
• Postictal confusion, amnesia and dysphasia with dominant hemisphere onset.
• Memory impairment, depression, anxiety and interictal psychosis in some.

Red flags.

• Seizures that fail 2 appropriate drugs.
• Progressive memory loss, acute confusion or limbic features (autoimmune encephalitis).
• Prolonged seizures or cluster episodes.

• EEG shows anterior temporal spikes; video EEG telemetry records seizures and defines the onset zone.
• MRI with epilepsy specific sequences: hippocampal atrophy, increased FLAIR signal, or another lesion.
• Neuropsychological assessment, and FDG-PET, SPECT or magnetoencephalography when MRI is non-diagnostic, in surgical evaluation.
• Screening of antibodies when onset is acute or atypical.

Differential diagnosis. Syncope, panic attacks, psychogenic non-epileptic seizures, migraine aura, transient epileptic amnesia, autoimmune encephalitis, parasomnias and frontal lobe epilepsy.

• First line drugs for focal seizures: lamotrigine or levetiracetam; carbamazepine is an alternative.
• Lamotrigine 25 mg orally once daily for 2 weeks, then 50 mg daily for 2 weeks, then increases of 50 to 100 mg every 1 to 2 weeks to a usual 100 to 200 mg daily in 1 or 2 doses. Maximum 400 mg daily (200 mg daily with valproate, 600 mg daily with enzyme inducers). Monitor rash, Stevens-Johnson syndrome and drug interactions. Reduce dose in moderate to severe hepatic impairment; no renal dose change, with caution in severe disease; acceptable in pregnancy with monitoring of levels.
• Levetiracetam 500 mg orally twice daily, increased by 500 mg twice daily every 2 weeks as needed to a maximum of 1500 mg twice daily. Monitor mood, irritability and renal function. Reduce dose when creatinine clearance is 50 to 80 mL/min (500 to 1000 mg twice daily), 30 to 50 mL/min (250 to 750 mg twice daily) and under 30 mL/min (250 to 500 mg twice daily). Acceptable in pregnancy.
• Carbamazepine modified release 100 to 200 mg orally once or twice daily, increased by 100 to 200 mg every 1 to 2 weeks to a usual 800 to 1200 mg daily. Maximum 1600 mg daily. Monitor sodium, full blood count, liver function and levels. Check HLA-B*1502 in people of Han Chinese, Thai or other at risk Asian ancestry before starting; avoid in atrioventricular block; reduce dose in hepatic impairment; many drug interactions (including reduced hormonal contraceptive efficacy); use only when needed in pregnancy.
• After 2 adequate drug regimens fail, refer for surgical evaluation: anterior temporal lobectomy or selective amygdalohippocampectomy gives seizure freedom in about 60 to 70% versus under 10% with continued drugs. Neuromodulation (vagus nerve stimulation, responsive neurostimulation) is for those not suitable for resection.
• Seizure safety counselling: bathing, driving, heights, and sudden unexpected death risk.
• Screen for depression and anxiety; supportive neuropsychology.

Monitoring. Review every 6 to 12 months; drug levels where relevant; sodium on carbamazepine.

Referral and escalation. Epilepsy centre early for drug resistant disease; urgent review for status or encephalitis features.

Special groups. Women: pregnancy planning and folic acid 5 mg orally once daily before conception through the first trimester (maximum 5 mg daily; no monitoring beyond B12 status; no renal adjustment). Older adults: reduced doses and bone health review on enzyme inducing drugs.