Clinical correlations of photoparoxysmal responses

Reilly and Peters (1973) reported that photoparoxysmal responses (PPRs) that outlasted the stimulus correlated significantly with seizures as compared to self-limited PPRs. However, they defined a wide range of activity, including occipital spikes and slow wave bursts, as PPR. We examined EEGs of 3557 patients and 48 normal subjects for PPRs defined only as generalized spikes or spike-wave activity. None of the 48 normal subjects showed a PPR. PPRs were seen in 35 (1%) patients, 27 (77%) of these had a definite history of epilepsy, 3 (9%) had a questionable history, and 5 (14%) had had no seizures. PPRs were prolonged more than 100 msec beyond the stimulus in 11, and self-limited in 24. The incidence of seizures was not statistically different in these 2 groups. Furthermore, the classification of PPRs into these 2 groups could be influenced by the time at which the stimulus was stopped after the appearance of the PPR. PPRs are rare in normal subjects and non-epileptic patients and have a high correlation with seizures irrespective of their relationship to the strobe stimulus.