Photosensitive Epilepsy

Photosensitive epilepsy is a reflex epilepsy in which seizures are triggered by flashing lights or patterns, with an abnormal photoparoxysmal response on EEG. It is mostly seen in genetic generalised epilepsies, especially juvenile myoclonic epilepsy.

About 3 to 5% of people with epilepsy are photosensitive, and about 1 in 4,000 people in the general population have photosensitivity. Onset is mostly between 7 and 19 years, with a peak at about 12 to 13, and it is more common in girls.

Triggers. Flicker at 15 to 25 flashes each second, strobe lights, television and screens with flicker, video games, bright sunlight through trees or water, high contrast patterns (stripes) and red blue colour changes.

Course. Photosensitivity often declines in adulthood, but seizures can continue. Sleep deprivation, alcohol and fatigue lower the threshold.

Pathophysiology.

Visual cortical hyperexcitability and impaired inhibition cause synchronised discharges when the visual system receives rhythmic stimuli. Spread to thalamocortical circuits produces generalised spike wave.

The genetic liability is polygenic, and the photoparoxysmal EEG response is inherited.

• Myoclonic jerks, absences or generalised tonic clonic seizures within seconds to minutes of a trigger.
• Focal visual or occipital features in some, with headache, nausea or visual symptoms before the seizure.
• Self-induction (waving a hand in front of the eyes) in a minority.
• Recurrent events in specific situations (discos, screens, sunlight).

Red flags.

• Prolonged seizure or status epilepticus.
• Seizures in an unusually young child or with developmental regression.
• Focal neurological signs.

• EEG with intermittent photic stimulation across frequencies (1 to 60 Hz), with eyes open, closed and during closure; a photoparoxysmal response is generalised spike wave or polyspike wave.
• Pattern stimulation testing and review of screen use when screen induced seizures are suspected.
• Video EEG when events are unclear; MRI for atypical features.
• Review for associated syndromes (juvenile myoclonic epilepsy, Jeavons syndrome).

Differential diagnosis. Non-photosensitive generalised epilepsy, occipital lobe epilepsy, migraine aura triggered by light, panic attacks, non-epileptic events and syncope.

• Trigger avoidance: use a screen with a refresh rate of 100 Hz or higher or an LCD or LED screen, sit at least 2 to 3 metres from a television, use a small screen in a well lit room, avoid flashing content, cover one eye or use polarised or blue tinted lenses, avoid strobe lights and sleep deprivation.
• Sodium valproate is the most effective first line drug in males: 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, because of major malformations and neurodevelopmental disorders.
• Levetiracetam, first line in girls and women of childbearing potential: 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.
• Lamotrigine as an alternative: 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 (stop at the first rash). Reduce dose in moderate to severe hepatic impairment; levels fall with oestrogen containing contraception and in pregnancy.
• Avoid carbamazepine, phenytoin and other drugs that can aggravate generalised epilepsy.
• Counsel on safe use of screens, television, video games and nightclubs.

Monitoring. Review every 6 to 12 months; repeat EEG for treatment decisions; assess adherence and sleep.

Referral and escalation. Epilepsy specialist for all women of childbearing potential and for drug resistant disease; ophthalmology or optometry for lenses.

Special groups. Women: pre-conception counselling 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).