Relación entre estructura y biodegradabilidad

Three clinical variants of benign focal epilepsies of childhood (BFEC) are recognised: benign epilepsy with centrotemporal or Rolandic spikes (BECRS), the most frequent form; childhood epilepsy with occipital paroxysms and benign psychomotor epilepsy (Metz-Lutz and Massa, 1999). This section will concentrate on BECRS, as the variant with the greatest potential relevance to language deficits associated with malaria. BECRS is the most common focal epilepsy of childhood, accounting for between 13 and 23% o f all childhood epilepsies (Wirrell, 1998). Peak onset is between 7 and 8 years, although the syndrome may occur at any time between 3 and 13 years o f age. The characteristic EEG manifestation is of blunt, high-voltage centrotemporal spikes, often followed by sleep-activated slow waves that tend to spread from side to side. Seizures classically occur during sleep and are often infrequent, with 13-21% of patients experiencing only a single seizure (Wirrell, 1998).

Several authors have considered BECRS to be a useful research model, overcoming many of the methodological problems confronted when investigating the complex interactions between cognitive function and epilepsy. Despite the focal nature o f the seizures and EEG characteristics, there is no anatomical brain lesion and the prognosis is benign regardless of the antiepileptic drug therapy. Finally, most seizures occur at night and may not present as convulsions and the patient and his or her family and friends know the prognosis is benign, both o f which may reduce the negative sociocultural consequences associated with a diagnosis of epilepsy (D'Alessandro, et al., 1990; Piccirilli, et al., 1994).

Although, as its name suggests, the syndrome is considered to be benign, it is not clear whether its ‘benign nature’ refers to seizure manifestations, normalisation of the EEG, normal psychomotor development or all three (Croona, et al., 1999). A number of studies have contested the ‘benign’ label attributed to BECRS, although the nature of the problems is variable. Poor performance on cognitive assessments measuring IQ (Weglage, et al., 1997; Yung, et al., 2000), aspects of memory (Croona, et al., 1999; Weglage, et al., 1997), executive functions (Croona, et al., 1999) and attention

(Piccirilli, et al., 1994) have variously been reported. Impairments in speech

production (Deonna, et al., 1993), fine motor performance (Weglage, et al., 1997) and behaviour (Yung, et al., 2000) have also been described.

More consistently, deficits in language functions have been identified (Deonna, et al., 2000; Staden, et al., 1998; Yung, et al., 2000), although Weglage and colleagues (1997) maintain that verbal functions were less affected than non-verbal functions in his patients. Deonna and colleagues (2000) describe three of their cohort of 22 children with ‘developmental dysphasia’ or delayed language development. Impairments were phonological and/or lexicosyntactic in character and improved over the three year follow-up period but did not resolve completely. Aphasie impairments have also been described by Yung and colleagues (2000), who report three children with an acquired epileptic aphasia in association with BECRS, one of whom had initially presented with a profile compatible with delayed language development. They interpret their findings as suggesting that the same epileptic process can interfere with language function at two different times in its evolution, causing a developmental language delay before the onset of spoken language and an acquired aphasia after the

acquisition of language. Other studies have documented more isolated problems in semantics (D'Alessandro, et a l, 1990; Deonna, et al., 2000), word finding, phonology, oromotor functions (Deonna, et al., 1993), reading and spelling (Deonna, et al., 2000). Staden and collègues (1998) administered a detailed battery o f language assessments to 20 children with BECRS. Thirteen presented with a consistent pattern o f mild to moderate language dysfunction, eight of whom had widespread deficits in up to eight of the 12 assessments. Impairments were concentrated in the areas o f reading/spelling single words, auditory verbal learning, expressive grammar and auditory discrimination with background noise. The authors suggest that the deficits are indicative of a specific language impairment as IQ was assessed as normal in eight of the 13 children with language problems.

Other studies have found that although children with BECRS have more scholastic and neuropsychological problems as a group than controls, no single cognitive profile to characterise the group emerges (Deonna, et al., 2000). Some studies suggest that impairments identified would be unlikely to have any appreciable consequences in daily life, although they may adversely affect the more complex levels of information processing and result in behavioural problems and school adjustment (D'Alessandro, et al., 1990). Several authors have linked the cognitive problems with the intensity of paroxysmal activity (D'Alessandro, et al., 1990; Deonna, et al., 2000; Metz-Lutz and Massa, 1999). Baglietto and colleagues (2001) found that children with BECRS had poorer visuomotor coordination, non-verbal short term memory, sustained attention, picture naming and visual-perceptual ability compared to controls at interictal

epileptic discharge (lED) activation during sleep. At spontaneous or treatment-

induced lED remission, there were no differences between children with BECRS and controls.

The persisting question in BECRS is whether the EEG abnormalities play a direct role in causing developmental and neuropsychological problems or whether they are

simply non-specific markers of an underlying encephalopathy. The disorder is

considered to have a genetic component as there is an increased prevalence o f various types o f epilepsy in patients’ families (Willmore and Ueda, 2002) and one third of siblings or first degree relatives have identical EEG abnormalities (Weglage, et al.,

deficits seen in BECRS. Early and prolonged focal epileptic activity, even at a subclinical level, may affect neuronal networks in the process o f specialisation and lead to the development of abnormal neuronal connections (Deonna, 2000) or neuronal degeneration (Wasterlain and Shirasaka, 1994). The findings of Deonna and colleagues' (2000) study suggest the epilepsy played a direct role in the cognitive impairments seen in their participants: in the three participants whose EEGs worsened,

language and learning problems increased. However, the relationship between

cognition and EEG discharges is a complex one: not only can epileptiform discharges affect cognitive performance but activities such as reading, playing music or nonspecific cognitive activity can affect discharge rates (Binnie, 2001).

The experience of BECRS suggests that paroxysmal activity alone may be sufficient to disrupt cognitive processes, even in the absence o f organic brain damage, the negative effects of antiepileptic drug therapy and adverse sociocultural conditions (D'Alessandro, et al., 1990; Piccirilli, et al., 1994).