Reflex Epilepsy

Reflex epilepsy is epilepsy in which seizures are consistently triggered by a specific sensory or cognitive stimulus. Triggers include visual flicker, reading, music, sudden startle, hot water, eating, movement, touch and thinking tasks.

Reflex seizures occur in about 4 to 6% of people with epilepsy, most commonly photosensitive seizures. Onset is usually in childhood or adolescence.

Types. Visual (flicker, patterns), reading epilepsy, musicogenic epilepsy, startle epilepsy, hot water epilepsy (common in southern India), eating epilepsy, praxis induced epilepsy, somatosensory epilepsy, and cognitive triggers such as calculation or decision making.

Course. Seizure control with trigger avoidance and drugs is usual in genetic generalised forms; focal reflex epilepsies with a structural lesion, such as startle epilepsy in brain injury, tend to be resistant.

Pathophysiology.

Specific cortical networks respond to sensory or cognitive input with synchronised hyperexcitability, so a stimulus that engages that network triggers discharge.

Underlying genetic generalised or focal structural epilepsy lowers the threshold for these triggers.

• Seizures follow a reproducible stimulus within seconds to minutes.
• Reading epilepsy: jaw jerks and myoclonus while reading, sometimes progressing to a tonic clonic seizure.
• Musicogenic epilepsy: focal impaired awareness seizures from specific music.
• Startle epilepsy: sudden tonic seizures after an unexpected sound or touch.
• Hot water epilepsy: focal seizures with immersion in hot water.
• Spontaneous seizures also occur in many patients.

Red flags.

• Prolonged seizure or status epilepticus.
• Progressive neurological deficit or developmental regression.
• Focal onset with a structural lesion.

• Detailed history to identify the trigger, and a video EEG with provocation of the suspected stimulus.
• MRI with epilepsy specific sequences, particularly for startle, somatosensory and musicogenic epilepsy.
• Genetic or metabolic evaluation when features suggest a syndrome.
• Review for non-epileptic reflex phenomena and psychogenic triggers.

Differential diagnosis. Psychogenic non-epileptic seizures, syncope with a trigger, tics, hyperekplexia, paroxysmal movement disorders, panic attacks and migraine aura.

• Avoid or reduce the trigger when possible, and modify exposure (shorter reading periods, tepid water at lower temperature, avoiding particular music).
• Treat the underlying epilepsy syndrome: choose the drug by seizure type and sex.
• 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, behaviour 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.
• Sodium valproate: 600 mg orally daily in 2 divided doses, increased by 200 mg every 3 days to a usual 1000 to 2000 mg daily. Maximum 2500 mg daily. Monitor liver function, full blood count, platelets and weight. Avoid in liver disease, mitochondrial disease (including POLG variants), urea cycle disorders and porphyria. Contraindicated in girls and women of childbearing potential unless no alternative works and a pregnancy prevention programme is in place.
• 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. Maximum 400 mg daily (200 mg daily with valproate). Monitor for rash and Stevens-Johnson syndrome. Reduce dose in moderate to severe hepatic impairment; levels fall with oestrogen containing contraception and in pregnancy.
• Surgery is considered for focal reflex epilepsy with a resectable lesion that does not respond to 2 drugs.
• Safety counselling for bathing, heights and road use.

Monitoring. Review every 6 to 12 months; monitor seizure triggers, mood and drug levels where relevant.

Referral and escalation. Epilepsy specialist for structural or drug resistant disease; neuropsychology for cognitive triggers.

Special groups. Women: valproate pregnancy prevention programme and folic acid 5 mg orally once daily from before conception until the end of the first trimester (maximum 5 mg daily; no monitoring beyond B12 status; no renal adjustment).