Fixation-off sensitivity and generalized epileptic EEG induced by eyes closed

The current state of absence epilepsy: can we have your attention?

Absence seizures are common within many different epilepsies and span all the ages. Even though absence seizures were described more than three centuries ago advances associated with its classification, pathophysiology, genetics, treatment, prognosis, and associated co-morbidities continue to be made.

Metabolic correlatives of brain activity in a FOS epilepsy patient

The correlation and the interactions between neuronal activity and underlying metabolic dynamics are still a matter of debate, especially in pathological conditions. This study reports findings obtained on a subject suffering from fixation-off sensitivity (FOS) epilepsy, exploited as a model system of triggerable anomalous electrical activity. Functional Magnetic Resonance Spectroscopy was used to investigate the metabolic response to visual spike-inducing stimuli in a single voxel placed in the temporo-occipital lobe of a FOS epilepsy patient. MRS measurements were additionally performed on a control group of five healthy volunteers. The FOS patient also underwent an EEG session with the same stimulus paradigm. Uniquely in the FOS patient, glutamate and glutamine concentration increased during the first 10 min of stimulation and then returned to baseline. On the other hand, FOS-induced epileptic activity (spiking) endured throughout all the stimulation epoch. The observed metabolic dynamics may be likely linked to a complex interplay between alterations of the metabolic pathways of glutamate and modulation of the neuronal activity.

Absence seizures: a review of recent reports with new concepts

Absence seizures with bilateral spike-wave (SW) complexes at 3Hz are divided into the childhood form, with onset at around 6 years of age, and the juvenile form, with onset usually at 12 years of age. These seizures typically last 9-12s and, at times, are activated by hyperventilation and occasionally by photic stimulation. Generalized tonic-clonic (GTC) seizures may also occur, especially in the juvenile form. There may be cognitive changes, in addition to linguistic and behavioral problems. Possible mechanisms for epileptogenesis may involve GABAergic systems, but especially T-calcium channels. The thalamus, especially the reticular nucleus, plays a major role, as does the frontal cortex, mainly the dorsolateral and orbital frontal areas, to the extent that some investigators have concluded that absence seizures are not truly generalized, but rather have selective cortical networks, mainly ventromesial frontal areas and the somatosensory cortex. The latter network is a departure from the more popular concept of a generalized epilepsy. Between the "centrencephalic" and "corticoreticular" theories, a "unified" theory is presented. Proposed genes include T-calcium channel gene CACNA1H, likely a susceptible gene in the Chinese Han population and a contributory gene in Caucasians. Electroencephalography has revealed an interictal increase in prefrontal activity, essential for the buildup of the ictal SW complexes maximal in that region. Infraslow activity can also be seen during ictal SW complexes. For treatment, counter to common belief, ethosuximide may not increase GTC seizures, as it reduces low-threshold T-calcium currents in thalamic neurons. Valproic acid and lamotrigine are also first-line medications. In addition, zonisamide and levetiracetam can be very helpful in absence epilepsy.

Inverted fixation-off sensitivity in atypical benign partial epilepsy

Fixation-off sensitivity is an electroencephalographic phenomenon characterized by spike-and-wave discharges that only occur when central vision and fixation are eliminated. It is especially seen in children with Panayiotopoulos-type, early-onset, benign childhood occipital epilepsy or Gastaut type, late-onset, childhood occipital epilepsy. It can also be seen in eyelid myoclonia with absences, in other idiopathic generalized epilepsies, and in asymptomatic children without epilepsy. We describe a boy with atypical, benign partial epilepsy of childhood who exhibited the reverse: epileptiform activity that was suppressed by the absence of central vision or fixation, and activated by central vision or fixation.

Unusual focal ictal pattern in children with eyelid myoclonia and absences

Eyelid myoclonia is a type of epileptic seizure characterized by marked jerking of the eyelids, often associated with jerky upward deviation of the eyeballs. It can be triggered by eye closure. The ictal electroencephalographic pattern of eyelid myoclonia consists of generalized polyspike waves at 3 to 6 Hz. Eyelid myoclonia can be a component of the clinical seizures seen with idiopathic, symptomatic, or cryptogenic generalized epilepsy. The objective of this study was to describe the unusual focal ictal electroencephalogram features of two patients with developmental delay and eyelid myoclonia. To the best of our knowledge, this unique electroencephalogram finding was not previously described.