Reflex epilepsies (RE)
Incidence
Their prevalence varies from 1/3 000 to 1/700 for the most frequent forms (photosensitive epilepsies). RE may be classified into epilepsies that are primary or idiopathic (a genetic basis is likely) and epilepsies that are secondary or symptomatic (with an acquired basis). Primary RE frequently have a positive family history. The etiology of photosensitive epilepsy is unknown. A family history of epilepsy is reported in a great majority of patients. Other type of primary RE are non-verbal and verbal-induced seizures, but the genetics and incidence of it is not well reported, neither on secondary RE..
Clinical Characteristics
Reflex epilepsies (RE) are rare epileptic syndromes with seizures induced by specific triggering factors (either by visual, auditory, somato-sensitive or somato-motor stimulation, or by higher cortical function activities). It is considered an epileptic syndrome. Spontaneous seizures may also occur. RE may be classified into epilepsies that are primary or idiopathic (a genetic basis is likely) and epilepsies that are secondary or symptomatic (with an acquired basis). \"Reflex seizures\"\' can be also classified into a simple \"pure\" reflex epilepsy and a complex group. The former comprises seizure triggered by simple sensory stimuli or by movements (photosensitive epilepsies). The latter are triggered by complex mental and emotional processes (verbal and non-verbal epilepsies). Reflex epilepsies are generally considered as idiopathic. Primary RE frequently have a family history, an age of onset in early life, a benign prognosis and good response to medication (sodium valproate, lamotrigine), and an electroencephalogram (EEG) with a variable presentation but an almost invariable normality of background activity. Electroencephalographic seizures expression may be partial or generalized. In visually sensitive patients, myoclonic or tonic-clonic
seizures manifest typically at the age of 8-10 years; the risk of having visually-induced seizures then increases until after puberty, with a decline after the age of 25 years. Most patients (75%) have tonic-clonic, myoclonic, and absence seizures, whereas a minority (25%) have a history of partial seizures. Photosensitive patients typically have subtle eyelid myoclonic movements, jerks of the arms (mostly, symmetric), and massive jerks of the whole body. These signs occur with or without loss of consciousness and subjective symptoms. As described above, other type of primary RE are non-verbal and verbal-induced seizures. Such reflex seizures are rare and are sometimes very difficult to diagnose. The etiology of primary non-verbal and verbal-induced seizures is unknown. Non-verbal and verbal-induced epilepsies may be divided into epilepsies that are primary or idiopathic (with a genetic basis) and epilepsies that are secondary or symptomatic (with an acquired basis). Primary reflex seizures are precipitated by one and only one stimulus and occur under no other circumstance. Secondary seizures are induced by several triggers and spontaneous seizures occur.
Secondary RE occur at later age, frequently in patients with an associated neurologic and non epileptic impairment. There is sometimes less stereotypy in clinical expression, a poorer response to drugs used for focal seizures (like carbamazepine, phenytoin), and frequently an abnormal interictal EEG background.
Precipitants
The presence of a clear triggering factor should lead to restrictions concerning exposure to the trigger. The latency of seizure occurrence is influenced by many non-specific factors such as sleep deprivation, fatigue, alcohol intake and menstruation. Patients often recognize the initial symptoms and avoid prolonged exposure to the stimulus to prevent GTCS. Concentration of attention or stress may contribute to the precipitation of seizures.
Provocation Tests
Standard intermittent photic stimulation (IPS) procedure reports that photosensitive patients are most sensitive when photic stimulation is performed during eye closure (93%), they are less sensitive to seizures with their eye closed (81%), and they are least sensitive with their eye open (66%). Many patients do not have photoconvulsive response on the EEG if one eye light reception is prevented with the use of a hand or cardboard. Depending on the triggering stimulus, exposure to that stimulus may trigger a seizure or show abnormal EEG response on the video-EEG simultaneously performed. Verbal-induced epilepsies are associated with a subjective sensation of clicking, mouth trembling, stuttering, difficulty in pronouncing words and eventual speech arrest that may progress to a generalized tonic-clonic seizure (GTCS) if the stimulus persists. Concentration of attention or stress may contribute to the precipitation of seizures.
Diagnostic Procedures
It is a clinical-EEG diagnosis. Photosensitive epilepsy diagnosis is based on subjective symptoms and clinical signs, EEG recordings in response to intermittent photic stimulation (IPS) or a combination of these. In other types of RE, Video-EEG recording is a critical test to elucidate the clinical and EEG features of the induced seizures and the modalities of their precipitation. Ictal EEG recordings are used to as a major criterion as to whether reflex epilepsy is a localization-related or a generalized syndrome.