Occipital seizures induced by intermittent photic stimulation in Dravet syndrome

Dravet syndrome (DS) is a rare disorder with seizure onset in the first year of life, typically beginning with prolonged febrile hemiclonic seizures or generalized tonic-clonic seizures. Photosensitivity is reported in more than 40% of patients. We present two cases of DS in which we had the chance to record occipital seizures induced by Intermittent Photic Stimulation (IPS).

We retrospectively reviewed the medical records of 32 children affected by DS. All clinical notes were reviewed in order to evaluate the occurrence of seizures induced by IPS.

Among the 32 reviewed clinical records, two patients with IPS-induced seizures were found. In both patients seizures originated from the occipital-temporal region. Clinical history was characterized by generalized tonic-clonic seizures, and myoclonia. At the age respectively of 11 months and 20 months they presented a prolonged focal seizure induced by IPS at a frequency of 10 Hz. During the follow-up they additionally presented with hypomotor seizures, also induced by IPS during laboratory EEG examinations. The semiology of hypomotor seizures resembled what is described as "complex partial status", a type of non-convulsive status with ictal discharges arising unilaterally from the occipito-temporal region.

Based on available literature, IPS induced occipital seizures have not been reported during the first year of life. Although pathophysiological features are not yet completely understood, both photosensitivity and occipital seizures should be considered in the diagnostic evaluation in DS. The documentation of IPS induced occipital seizures might contribute to widen the clinical and neurophysiological spectra of DS.