Epilepsies characterized by seizures with a specific mode of precipitation occur in 4%–7% of patients with epilepsy.¹ More general factors such as stress, sleep deprivation, and fatigue may contribute to the exacerbation of seizures in up to 62% of patients.² Precipitants may be divided into simple and complex: simple precipitants include elementary sensory stimuli such as flickering light, color, patterns, somatosensory, proprioceptive, or startle, whereas complex precipitation implies relatively elaborate stimuli such as music and other complex auditory materials, eating, language, thinking, praxis, and experience/emotion.

These precipitants apparently relate to specific local or regional cortical function, and some precipitants activate symptomatic and focal epileptogenesis, whereas others activate idiopathic and generalized epileptogenesis. This chapter deals with reflex epilepsy or seizures in patients with idiopathic generalized epilepsy (IGE).

Somatosensory or proprioceptive stimuli usually induce focal seizures in patients with epilepsies of symptomatic or probable symptomatic origin, although there are some reports in patients with idiopathic epilepsy. Tapping may induce extreme spikes in children with benign Rolandic epilepsy,³ hot water precipitates focal seizures in familial cases,⁴ and specific auditory triggers (some also with complex linguistic modality) may operate in patients with lateral temporal lobe epilepsy with the LGI1 gene mutation.⁵

The common form of startle epilepsy occurs in patients with symptomatic etiology. However, Ricci et al⁶ and subsequent authors described several infants with myoclonic jerks provoked by startle stimuli and later by noise or contact. Seizure occurred before the age of 2 years, and seizure remission was rapid. The electroencephalographic (EEG) shows brief generalized polyspikes- or spike-wave complexes with the myoclonic jerks. This idiopathic type was designated as reflex myoclonic startle epilepsy in infancy and may be included in the syndrome of benign myoclonic epilepsy in infancy.⁷

Seizure induction by other sensations such as smell usually occurs in patients with a symptomatic etiology.

VISUALLY INDUCED SEIZURES

Visual sensitivity is the most common simple precipitant in patients with idiopathic generalized epileptogenesis and includes both flicker sensitivity and pattern sensitivity.⁸ A prevalence of photosensitivity, an abnormal response of the EEG to light stimulation consisting of a photoparoxysmal response (PPR), is estimated in the range of 0.3%–3%, although many studies are limited by subject-selection bias.⁹ Photosensitivity is higher in the young and female population. About one-third of photosensitive patients have epileptiform EEG abnormalities on viewing stationary striped patterns, and only a minority of patients sensitive to pattern are not sensitive to flicker.

The prevalence of visually induced seizures in the general population is <1 per 10,000, and the incidence 1 per 91,000 in the overall population.⁹ The Pokemon incident in Japan (1997) revealed that three of four photosensitive individuals had been unaware of their photosensitivity.

Sunlight, discotheque strobes, television viewing, movie screens, public displays, or videogames are common environmental triggers. Factors such as flicker rate, pattern, luminous intensity, color, size, location, and stimulus duration contribute to seizure precipitation.¹⁰ Intensities of 0.2–1.5 million candlepower are in range to trigger seizures. Frequency (flash rate) in the range of 15–25 Hz is most provocative.⁹ Patients with IGE are sensitive to the intermittent light stimulation containing wavelength spectra of approximately 700 nm.¹¹

Pattern sensitivity is enhanced by pattern vibration. Some patients are sensitive to eye closure. Abolition of central vision and fixation may also precipitate seizures. Some patients induce attacks with maneuvers producing visual stimulation. Game play may involve not only photo- or pattern stimuli, but also specific nonvisual triggers such as thinking, possibly with decision making, and hand movement, in addition to nonspecific factors such as fatigue by prolonged play and sleep deprivation.¹²

To avoid the risk of triggering seizures, the followings practices are recommended:^13,14,15 limiting bright flashes at >3Hz; light–dark stationary, oscillating, or reversing patterns should not have more than five stripes, unless they are restricted to <25% of the screen or are <50 cd/m² in brightness. Transition to or from saturated red is also considered to be a risk. People with epilepsy or known photosensitivity are advised to sit >2 m from any screen, to use good ambient lighting to reduce contrast, to avoid looking at rapidly flashing lights or alternating geometric patterns. Closing one eye or looking away from the image is of more benefit than closing both eyes. The effectiveness of nonpharmacologic treatment using sunglasses in controlling PPR was also reported.^16,17

Binnie¹⁸ reviewed mechanisms of photosensitivity with respect to activation of generalized seizures, and concluded that the visual cortex plays a crucial role in photogenic epileptogenesis and the generalization of discharges is secondary. He suggested that cortical hyperexcitability in generalized epilepsy is not uniform and may differ in degree and extent.

Myoclonus, absences, and generalized tonic–clonic seizures (GTC) are the typical clinical manifestations, but visual symptoms and lateralizing features may occur. Taylor et al¹⁹ noted previously unrecognized focal clinical and EEG occipital features in juvenile myoclonic epilepsy (JME) and suggested an overlap between JME and idiopathic photosensitive occipital lobe epilepsy, a syndrome defined as an idiopathic localization-related epilepsy with seizures of phosphen, blindness, or blurring of vision, often followed by head and eye deviation.²⁰

Complex precipitants involve higher brain function or mental processes, often associated with emotion. These complex triggers include: (1) verbal precipitation such as talking, reading, and writing; (2) nonverbal precipitation such as hearing music, game playing, decision making, drawing, solving mathematics, spatial thinking; and lastly (3) specific emotional precipitants.

Seizures induced by higher brain function may also be due to idiopathic or symptomatic etiologies, and may be focal or generalized. The latency from provocation is generally longer than for simple reflex seizures. The triggers often overlap. There may also be a contribution from nonspecific factors such as sleep deprivation.

In 1954, Bickford et al²¹ reported reflex idiopathic epilepsy induced by reading. He described three cases where prolonged reading gave rise to convulsions preceded by an aura of clicking or jaw movement. There were subsequent descriptions of seizures induced by various other cognitive activities such as calculating, writing, game playing, using language, decision making, drawing, and thinking, the majority of which were generalized.