Relationship between prolonged and self-limited photoparoxysmal responses and seizure incidence: study and review.

Photoparoxysmal responses (PPRs) are generalized epileptiform abnormalities occurring during photic stimulation. Prolonged PPRs, which outlast the stimulus, can be distinguished from self-limited PPRs, which cease spontaneously or when the flashes stop. Reilly and Peters (1973) found a higher incidence of seizures in patients with prolonged, rather than self-limited, PPRs. More recently, Jayakar and Chiappa (1990) reported a similar seizure incidence in the prolonged and self-limited groups. In order to assess these discordant results, we reviewed EEG records performed in our laboratory from 1983 to 1988. Sixty-eight EEGs had PPRs (19 prolonged and 49 self-limited). Patients with PPRs had a significantly higher incidence of seizures than controls (total patients versus controls, p less than 0.001; prolonged subgroup compared to controls, p less than 0.001; self-limited subgroup versus controls, p less than 0.01). Comparing PPR groups, we found that a prolonged PPR was associated with a higher incidence of seizures than a self-limited response (p less than 0.05); however, patients with a prolonged PPR more often had other epileptiform abnormalities than the self-limited group (p less than 0.001). There was no difference in seizure incidence between the PPR groups when comparing patients whose EEGs also contained other epileptiform abnormalities. Meta-analysis suggests apparent differences among the three studies are superficial.