Department of Clinical Neurophysiology and Epilepsies, Guy’s & St. Thomas’ NHS Foundation Trust, London, UK
Purpose. To define the spectrum of the epileptic syndromes and epilepsies (other than the idiopathic epilepsies of childhood with occipital paroxysms) that can be associated with fixation-off sensitivity (FOS), delineate the electrographic types of FOS abnormalities and identify the patterns that can be associated with clinical seizures, and examine whether there may be a pure form of fixation-off sensitive epilepsy. Methods. We reviewed the clinical and video EEG data of all our patients with FOS over the last 12 years. Children with idiopathic focal epilepsies and occipital EEG paroxysms were excluded. Results. From January 1995 to December 2006, 19 of about 8,500 patients had had one or more video-EEGs with FOS, yielding an approximate incidence of 0.2%. From the 14 patients with full clinical and EEG data available, 12 had various epilepsies that included IGE phenotypes (7), symptomatic or probably symptomatic focal (3), cryptogenic generalised (1), and adult onset idiopathic photosensitive occipital (1), and two had no seizures. Seven patients (50%) were photosensitive. FOS EEG abnormalities were occipital in six patients, generalised in eight, and generalised with posterior emphasis in two patients. Seven of these patterns were associated with habitual seizures in seven patients, but actual FOS-induced seizures (absences) were documented with video EEG in only one patient; three others had some historical evidence suggesting that, under some circumstances, their FOS EEG abnormalities might generate clinical seizures. Conclusions. Despite the association of FOS with generalised and focal, symptomatic and cryptogenic and mild or pharmaco-resistant epilepsies, closer analysis of our data, and supportive evidence from functional imaging and physiological observations on alpha rhythm generation, disclose a prominent role of the occipital areas, even when FOS EEG abnormalities and seizures are ostensibly generalised. Although FOS appears to be of relatively low epileptogenicity, an electroclinical profile of pure FOS epilepsy may exist [Published with video sequences].