Surfactantes de origen natural

TLE is a common cause of complex partial seizures (CPS): although the temporal lobe is the most common site of origin, seizures may arise in other lobes (Paradiso, et al., 1995) or regions outside the temporal lobes, for example the frontal pole, ffonto- orbital cortex or cingulate gyrus (Eiger, 2000) or elsewhere.

The ILAE classification describes temporal lobe seizures as originating from either hippocampal (mesiobasal limbic or primary rhinencephalic psychomotor) or lateral temporal areas. Many epileptologists adopt an aetiological approach and divide TLE into three types:

1) Mesial temporal epilepsy, associated with hippocampal sclerosis

2) Lesional temporal lobe epilepsy, defined by lesions other than hippocampal sclerosis in the temporal lobe

3) Cryptogenic temporal lobe epilepsy (Wieser, et al., 2000)

Approximately one third of children with TLE have no underlying temporal lobe lesion, no associated psychological deficits and show seizure remission in later childhood (Harvey, 2000). Seizure signs and the course of seizure spread may be different in children compared to those in adults due to the nature of the developing brain and auras cannot be reported (Nordli, et al., 2001). The typical phenomena of TLE only occur in children above five or 6 years of age (Brockhaus and Eiger, 1995; Eiger, 2000).

3 .7.1 Mesial temporal lobe epilepsy

Temporal lobe epilepsy associated with its most common pathological substrate, mesial temporal sclerosis, has resulted in the distinct epileptic syndrome of mesial temporal lobe epilepsy (MTLE) (Harvey, et al., 1995; Harvey, et al., 1997). This syndrome is of particular interest in the consideration of epilepsy and child development because the limbic system, which consists o f the amygdalae, septum, cingulate gyrus and hippocampal formation (Crossman and Neary, 1995), is involved in memory, affect and behaviour.

The seizure semeiology of MTLE is often auras - typically epigastric sensations

associated with olfactory, gustatory and psychic phenomena such as fear, déjà vu or

déjà entendu) - evolving into CPS with ictal, postictal, de novo or reactive

automatisms. Automatisms are commonly oroalimentary symptoms such as lip-

movements. Wieser and colleagues (2000) classify such seizures into three groups. First, absence-like seizures; secondly, seizures characterised by automatisms and psychomotor symptoms and thirdly, seizures with psychosensory, cognitive or emotional symptoms characterised by visual, auditory, somesthetic or olfactory illusions or psychic symptoms.

The causative role of hippocampal sclerosis in MTLE is controversial. There is some debate as to the prevalence of mesial temporal sclerosis in TLE in childhood with some paediatric series suggesting that it is a rare cause (Wyllie, et al., 1993) while others suggest prevalence rates as high as 75% (Cross, et al., 1996; Mohamed, et al., 2001). One of the most contentious issues in epileptology is whether prolonged

febrile seizures cause mesial temporal sclerosis. Many population-based and

prospective studies have failed to find any association (Lado, et al., 2000; Shinnar and Glauser, 2002) and preventing febrile seizures does not result in a reduction in the incidence of subsequent epilepsy, which would be expected if a causal relationship

existed (Shinnar, 1998). However, Maher and McLachlan (1995) found an

association between febrile seizures over 90-100 minutes in length and TLE with mesial temporal sclerosis. Febrile seizures lasting more than 90 minutes occur in less than 1% of cases (Berg and Shinnar, 1996), although prolonged status epilepticus may

be more common in a malaria-related context. Investigating children with CM,

Crawley and colleagues found that 28% of children had an episode of status epilepticus, which was longer than 30 minutes in 83% of this group (median 150 minutes, range 40-390 minutes) (Crawley, et al., 2001; Dr J Crawley, personal communication). It has not been possible to exclude the possibility that the immediate cause of an early childhood seizure, such as an infectious or ischaemic insult, may also cause injury in the mesial temporal region, which may in itself prove to be epileptogenic (Lado, et al., 2000). In such a scenario, mesial temporal sclerosis occurs independently o f seizures but is the immediate cause of epilepsy.

3.7.2 Developmental impairments associated with TLE

The neurobiology of TLE is more complex than the lesion model o f focal brain damage that gave rise to classic neuropsychological paradigms: a diagnosis of TLE

may indicate little about the child’s cognitive and behavioural profile (Paradiso, et al., 1995; Shulman, 2000).

In their seminal study on the long-term effects of TLE, Ounsted and colleagues (1987) found that 30% of the 100 children they followed for 38 years had psychosocial problems and were completely dependent on others and 32% required special

schooling. In a study using comprehensive neuropsychological assessments,

Schoenfeld and colleagues (1999) found a pattern o f generalised cognitive impairment in children with CPS and suggest that regions outside the epileptogenic focus were adversely affected. The pattern of impairments, although the result o f epilepsy of much shorter duration, was similar to that found in adults with CPS (Hermann, et al.,

1997), leading Schoenfeld and colleagues to propose that such generalised cognitive

effects may be intrinsically associated with early-onset CPS. Studies on

developmental level and IQ have indicated that IQ is lower in children with bilateral temporal lobe foci (Jambaque, et al., 1993). Gadian and colleagues (1996) found that left-sided temporal lobe pathology, as detected by magnetic resonance spectroscopy (MRS) is associated with a reduction in verbal IQ (VIQ) and right-sided pathology with a reduction in performance IQ (PIQ), although others have found no VIQ/PIQ discrepancy related to laterality of pathology (Jambaque, et al., 1993).

Language functions may be particularly affected in children with CPS, in both expressive and receptive domains (Schoenfeld, et al., 1999; Shulman, 2000). A PET study in adults with left TLE found the areas of greatest metabolic depression to be in left inferior frontal and superior temporal regions, which correlate to Broca’s and Wernicke’s areas respectively (Arnold, et al., 1996). No comparable study has been carried out in children. In addition to linguistic impairments, communication abilities may be adversely affected in TLE. Children assessed before temporal lobectomy and children with CPS have been found to have impairments in thought processing and discourse cohesion (Caplan, et al., 1993; Caplan, et al., 1994). More recently, Caplan and colleagues have found that children with CPS made more syntactic revisions than controls, making their speech sound stilted, artificial and detailed (Caplan, et al., 2001). The fact that these findings were particularly pronounced in participants with EEG evidence of a temporal lobe focus suggests that repair o f basic linguistic functions involves the temporal lobe, in contrast to higher level linguistic planning,

which appears to involve the frontal lobes. Anomia may be a particular feature of language impairment (Hamberger and Tamny, 1999) and may account for some of the verbal memory deficits associated with left TLE (Hermann, et al., 1988; Mayeux, et al., 1980). The results of a study by Billingsley and colleagues (2001) indicate greater participation o f regions outside the left temporal lobe in language functions in adults with left TLE, leading them to suggest possible inter- and intra-hemispheric functional reorganisation o f language representation.

The importance of medial temporal lobe structures in memory function is well- recognised. This has come largely from the study of memory in patients who have undergone temporal lobectomy for intractable epilepsy, emphasising the contributions o f left and right temporal lobe systems for verbal and non-verbal material respectively (Paradiso, et al., 1995). Memory impairment is commonly found in TLE, particularly MTLE associated with hippocampal sclerosis (Rausch and Babb, 1993; Sass, et al., 1995). Studies suggest that episodic memory is dependent on the hippocampus (Vargha-Khadem, et al., 1997) and is particularly affected in the case of bilateral hippocampal pathology. There is some evidence for the effects o f laterality on verbal and non-verbal memory (Helmstaedter, et al., 1994), although most studies have shown that children with both left and right TLE show deficits in both modalities of memory (Oxbury, 2000).

Behavioural impairments have also been linked to TLE: their heterogeneity is increasingly recognised as a consequence of the syndrome's complex neurobiology involving neuropathological factors and variable neurophysiological factors (Shulman, 2000), in addition to the psychosocial factors outlined in section 3.3.1. However, apart from later psychosis, which is commonly associated with TLE, children with this form of epilepsy do not seem to have more behaviour disturbances than children with other types of epilepsy (Caplan and Austin, 2000).