UNDERSTANDING CHILDHOOD ABSENCE EPILEPSY.
Childhood Absence Epilepsy (CAE) is thought to be a general form of epilepsy which is believed to affect the entire brain (Chen, Lu, Pan, Zhang, Wu, Xu & Ding, 2003). CAE is an idiopathic and generalised non-convulsive form of epilepsy (Crunelli & Leresche, 2002). It This disorder accounts for 10% to 17% of all cases of epilepsy diagnosed in school-aged children (Jallon & Latour, 2005). CAE is characterized by a multifactorial genetic aetiology (Matricardi, Verrotti, Chiarelli, Cerminara & Curatolo, 2014). This disorder is thought to result from interactions between genetic and acquired factors, although this is still debated (Matricardi et al, 2014). In terms of its genetic epistemology it has been argued that in 15% to 44% of CAE cases there is a positive family history of epilepsy in either the parents or siblings (Medina, Bureau, Hirsch & Panayiotopoulos, 2012). Epilepsy twin studies confirmed a concordance rate significantly higher in development of epileptic syndromes such as CAE (Reid, Berkovic & Petrou, 2009; Corey, Pellock, Kjeldsen & Nakken, 2011). More specifically, the genes implicated in CAE consist of [gamma]-amino-butyric acid (GABA) A and B receptors (GABRG2, GABRA1, BABRB3 [Yalcin, 2012]). These genes contribute towards "thalamocortical dysrhythmia" and gene mutations encoding this particular pattern of activity (Yalcin, 2012). However, despite the robust genetic aetiology of CAE, genes involved and mode of inheritance still remain unidentified (Corey, Pellock, Kjeldsen & Nakken, 2011).
The Neural Correlates of Childhood Absence Epilepsy
The primary characteristics of CAE are the very frequent absence seizures (Jallon & Latour, 2005). In terms of its neurophysiologic correlates, it is well established that CAE is characterised by a distinct 3-4 Hz wave and spike discharge observed in the Electroencephalogram (EEG [Blumenfeld, 2012]). This pattern of EEG activity corresponds to temporary loss of consciousness, behavioural arrest, and unresponsiveness and it can last for very brief periods of 5-10s (Loiseau, Panayiotopoulos & Hirsch, 2002). This is the essential feature of absence seizures in CAE (Blumenfeld, 2012). The variations in consciousness deficits from one seizure to another are also important features of absence seizures (Berman, Negishi & Vestal, 2010).
A number of neurophysiological studies have consistently demonstrated that at diagnosis and even during childhood patients who are affected by CAE have behavioural disorders, as well as cognitive and linguistic impairments (Caplan, Siddarth & Stahl, 2008; Kernan, Asarnow & Siddarth, 2012). Cognitive difficulties may involve particularly executive functions and the attentional domain (Pavone, Bianchini, Trifiletti, Incorpora, Pavone, Parano, 2001; D'Agati, Cerminara, Casarelli, Pitzianti, Curatolo, 2012). Furthermore, EEG evidence also points to verbal difficulties and deficits in visuospatial memory (Nolan, Redobaldo & Lah, 2004; Henkin, Sadeh & Kivity, 2005). Ictal and postictal features in EEG research have documented that some of the associated ictal features in CAE consist of 3Hz regular eyelid movement, and irregular and inconsistent eye opening, particularly during seizures in which the eyes were initially closed (Sadleir, Farrell, Smith, Connolly & Scheffer, 2006). Other EEG studies (see Sadleir, Scheffer & Smith, 2008; Sadleir, Scheffer, Smith, Carstensen, Farrell & Connolly, 2009) have also been used in the diagnosis of other CAE features such as photic stimulation, and hyperventilation. In this respect, one should note that intermittent photic stimulation and hyperventilation have been found to induce the absence of seizures in at least 21% and 83% of patients, respectively. CAE interictal EEG activity can be characterized by normal background activity (Sadleir, Scheffer, Smith, Carstensen, Farrell & Connolly, 2009).
However, interictal paroxysmal activity from generalised spike-waves discharges has been found in up to 92% patients (Sadleir, Scheffer & Smith, 2008). In this respect, Sadleir, Scheffer and Smith (2008) analysed the extent to what specific factors such as age, state of arousal, epilepsy syndrome somehow determines specific features of absence seizures. More specifically, they used electroencephalography (EEG) methods as means of analysing level of awareness, eyelid movements, and eye opening during seizures. In this way, they evaluated 509 seizures on a sample of children (n= 70) with Childhood Absence Epilepsy. They found an association between age, level of awareness, and eye opening. From the 383 seizures with clinical signs they found that abnormal eyelid movements occurred in 228 (60%), and clinical seizures occurred in 56 (80%) of patients. They also demonstrated that there was ~ 3-Hz rhythmic eyelid movements in 159 (42%) patients. In this respect, abnormal eyelid was significantly more likely to occur in longer seizures (p=0.001). Based on this pattern of results they have also postulated that age independently influenced eye opening and level of awareness. Similar EEG studies have also demonstrated that 50% of seizures in CAE consisted of typical spike-wave morphology in their initial generalized discharge (Seneviratne, Cook & D'Souza, 2012). Moreover, discharges can also develop some degree of irregularity towards the end of the seizure, particularly during sleep, hyperventilation, sleep and drowsiness (Kernan, Asarnow & Siddarth, 2012).
Treatment and Prognosis
The prognosis for CAE is somewhat inconclusive given that they largely differ in inclusion and inclusion criteria, diagnosis, and key definitions (Matricardi et al, 2014). Variable prognoses at different stages are contingent upon the length of follow-ups (Matricardi et al, 2014). For instance, in a well-known study carried out by Seneviratne, Cook and D'Souza (2012), children affected by CAE exhibited an overall good prognosis, whereby only 7% of children were still having seizures 12-17 years of follow up. In terms of treatment and therapeutic interventions, one of the most prominent forms of treatment consists of administering of drugs such as Ethosuximide (ESM), and Valproate (VAP). For instance, ESM is thought to allow complete control of CAE in up to 70% of treated patients (Blomquist & Zetterlund, 1985). When it comes to examining the effects of VPA some have reported (see Covanis, Gupta & Jeavons, 1982) seizure-free rates varying from 88% to 95%.
In conclusion, it should be evident that CAE is a very prominent paediatric epileptic syndrome. Correct diagnosis of CAE relies heavily upon well-known seizure types associated with EEG features. Its clinical expression is thought to be largely contingent upon both genetic and acquired factors. Finally, the present paper has demonstrated that CAE can impair a wide range of cognitive and behavioural functions. Therefore, when it comes to effectively treating this disorder, early detection is paramount.
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|Author:||Palmer, Laura Scott|
|Publication:||Journal of Social and Psychological Sciences|
|Date:||Jan 1, 2017|
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