Activation procedures, hyperventilation, intermittent photic stimulation and sleep enhance the epileptiform abnormalities and also help to identify seizure precipitating factors. Absence seizures have a special tendency to get precipitated during hyperventilation. The photoparoxysmal response, defined as the occurrence of generalized spike, spike-wave or polyspike wave discharges consistently elicited by intermittent photic stimulation,49 has a high correlation with primary generalized epilepsy.13,50 A proportion of patients with photosensitivity may exhibit a similar EEG response to geometric patterns.13,50 There are some racial differences in the reported prevalence of photoparoxysmal response. In White subjects with epilepsy it varied between 4 to 6%.49-51 A lower prevalence was reported in the African and Asian population with epilepsy, 0.4% to 1.6%.52-54 However, in a recent study from south India, the prevalence was similar to the studies among Whites, 3.5%.55 The wide variations observed in these studies may be related to the differences in the characteristics of the patient group studied and the study protocol. Patients with suspected reflex epilepsies should be subjected, during EEG recording, to appropriate stimuli that precipitate seizures.56 Cognitive tasks should include reading, speaking, listening to conversation, arithmetic calculation, writing, drawing and working crossword puzzles.57-60
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