Periodic complexes and alternating rotatory nystagmus with cyclic pupillary changes

[Pseudoperiodic and paroxysmal electroencephalographic activities]

Periodic and paroxysmal EEG patterns are frequent and easily recognized. They often correlate with particular neurological or systemic conditions. We propose a reclassification and critical examination of these periodic EEG patterns by reviewing the original work presented by J. Gaches in this journal some thirty years ago. Periodic EEG activity is still classified by its localisation--generalised or focal--and by its periodicity--long or short. Periodic long-interval diffuse paroxysmal patterns are reported with rare pathologies such as SSPE, trypanosomiasis or intoxication with phencyclidine. Suppression bursts (SB) may be found in two main situations post-anoxic encephalopathies and drug-induced comas. Ohtahara syndrome is a very rare childhood epileptic syndrome with SB. Periodic short-interval diffuse pattern have been reported in Creutzfeldt-Jakob disease but also in toxic encephalopathies, such as lithium intoxication or as recently reported in acute Cefepime intoxication as well as with metabolic encephalopathies and rarely during AIDS. Periodic lateralized epileptiform discharges (PLEDs) have been classified according to their morphology and the associated condition (epileptic seizures, subtle status, "vascular" seizure). The principal etiology is cerebro-vascular disease and herpes encephalitis but it has also been reported in several other neurological diseases.

Clinical accompaniments of the burst-suppression EEG pattern

A burst-suppression pattern on the EEG following anoxic insult is usually associated with a poor prognosis. Myoclonic jerks may accompany the electrographic burst. On rare occasions oral, ocular, or appendicular movements can be associated with bursts of EEG activity recorded following cerebral anoxic insult. At times these movements may cause confusion about the patient's state of consciousness or the purposefulness of the movements; they may mimic volitional movements in response to external stimuli. To better describe the variety of movements that may accompany bursts of EEG activity in comatose patients, we review 12 cases where movements occurred in association with the electrographic bursts.

Burst-suppression pattern with unusual clinical correlates

A 44-year-old man suffered a severe anoxic encephalopathy with rapid fatal outcome. His EEG prior to expiration showed a burst-suppression pattern (BSP) with occurrence of two previously unreported clinical features: spontaneous chewing movements during the burst and tonic posturing during the suppression phase. In coma the appearance of BSP in the EEG commonly implies a severe anoxic/metabolic insult to the brain with a grave prognosis. The pattern is considered to be interictal, except in cases presenting with myoclonic status epilepticus. Subtle intermittent movements of the eye, mouth and cardiovascular rhythm are uncommon and it is unclear whether these are epileptic events or not. This case indicates that the suppression phase can also have associated clinical signs.

Language-apparent reflex epilepsy

An adolescent with photosensitive epilepsy had absence seizures reproduced by forced voluntary eye closure in light or in darkness, independent of eyelid immobilization or ocular elevation. Attacks preferably occurred while speaking Spanish, her second language, mediated through brief, strong, automatic closing of the eyes during difficult word retrieval. Complex other multidirectional ocular movements or blinking, cognitive and language tasks were ineffective. Frontorolandic cortical epileptogenesis is seemingly responsible for light-provoked seizures in Papio papio, acting via hyperexcitable neuronal facial aggregates (i.e. Baba and Wada). Since orbicularis oculi muscle fibers mediating strong and weak contractions are differentially innervated by the facial nuclei, we submit that critical threshold tonic activation of specific nuclear aggregates explains this language-apparent reflex epilepsy, triggered by extreme eye closure. A "dopamine connection hypothesis" linking periodic eye closure, effortful memory and photosensitivity, based on its putative evolutive significance, is discussed.