Characteristics of the synchronous occipital and frontopolar spike phenomenon in Panayiotopoulos syndrome

Purpose: The synchronous appearance of an occipital and frontopolar spike (the Fp-O spike) is characteristic of Panayiotopoulos syndrome (PS). This phenomenon is also seen in various other types of epilepsy, particularly those that occur in childhood. Using dipole analysis and sequential mapping, we investigated the characteristics of the Fp-O spike observed in seven patients with PS and six patients with symptomatic localization-related epilepsy in childhood (SLE). Methods: We analyzed both one averaged spike and 20 manually selected successive individual Fp-O spikes for each patient through sequential topographical mapping with steps of 10 ms from 40 ms before to 40 ms after the negative maximum peak of each spike. For dipole analysis, a period of 40 ms before the maximum negative peak of the averaged spike in each patient was examined using equivalent current dipole localization software. Results: Sequential mapping revealed that occipital negative peaks preceded frontal negative peaks in all of the PS patients, as well as in two of the six SLE patients. The four remaining SLE patients did not exhibit preceding occipital peaks. In all of the patients with PS, representative dipole locations were in the posterior area, whereas in SLE patients they were scattered over more anterior areas. The estimated sources of the Fp-O and O spikes appeared to have the same position and orientation in the two PS patients. Conclusion: We conclude that Fp-O spikes in PS occur as the result of a rapid spread of epileptic activity from the posterior areas to the anterior areas of the brain. Fp-O spikes in PS patients show a uniform topographical pattern and dipole location, whereas those in other patients show more heterogeneity in these features. These findings support the homogeneity of PS and thus its designation as a syndrome.