Abstracts

Rationale: Photoparoxysmal response (PPR) on photic stimulation (PS) during EEG associated with abnormal motor manifestation or behaviour change is considered a provoked seizure. In the absence of an obvious associated clinical phenomenon, PPR is considered as interictal EEG signatures of cortical hyperexcitability and not a seizure. Subtle behavioural changes during PPR can easily go unnoticed. Simultaneous Motor Function Task MFT (as below) can detect subtle behavioral changes as slowness. Objective: To ascertain whether PPR during EEG represents a provoked seizure, even in the absence of obvious clinical manifestation during PPR, by using a simultaneous MFT. Methods: Patients were instructed and trained to squeeze a soft rubber ball attached to a pressure transducer at a regular rate (approximately 1 per second). The motor performance was digitally displayed on the EEG monitor synchronized to the brain waves. Any slowing of the motor task time-locked to PPR not associated with other obvious clinical change was considered as a positive response. Inclusion 1.EEGs during 1/2005- 5/2005 which showed PPR. 2.Children <18 yr. Exclusion Clinically obvious motor or behaviour change during PPR other than change in motor task. Measurement The average time interval between two successive motor response across a PPR will be compared to the average time interval between two successive motor response during photic stimulation not associated with PPR and during non-PS period. Results: 36 patients with PPR were identified. 3 had photoconvulsive response, MFT was not performed in 5 due to young age and 6 did not perform MFT consistently. 22 patients were included in the study (table 1). 13 children showed motor slowing during MFT. All the children with motor slowing during PPR had generalised epileptiform discharges during PPR. Of the 10 children with epilepsy and motor slowing during MFT, 5 had juvenile myoclonic epilepsy. 50% of children (3/6) without epilepsy also showed motor slowing during PPR.Conclusions: MFT reliably detected change in the behavioural state of patients in the absence of other obvious clinical changes which otherwise would have gone undocumented. This study also has demonstrated that in some children, PPR is associated with slowing in MFT and hence represents a provoked seizure. It is reasonable to believe that such a child has high likelihood of experiencing similar brief seizures in certain situations; viz, light flickering, rapid change of sun shade & light during travel etc. This could have significant impact in the safety of a teenage driver who has PPR in EEG, but no clinical seizures. We recommend that MFT be done routinely during photic stimulation part of EEG recording.