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, ...