Simple partial seizures (isolated auras) in medial temporal lobe epilepsy

Simple partial seizures (isolated auras) in medial temporal lobe epilepsy

Seizure 2004; 13: 247–249 doi:10.1016/S1059-1311(03)00192-4 Simple partial seizures (isolated auras) in medial temporal lobe epilepsy J. JANSZKY, R...

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Seizure 2004; 13: 247–249

doi:10.1016/S1059-1311(03)00192-4

Simple partial seizures (isolated auras) in medial temporal lobe epilepsy J. JANSZKY, R. SCHULZ & A. EBNER Epilepsy Centre Bethel, Bielefeld, Germany Correspondence to: Dr J. Janszky, M.D., Ph.D., Epilepsie-Zentrum Bethel, Krankenhaus Mara, Maraweg 21, Bielefeld 33617, Germany. E-mail: [email protected]

We analysed whether the medial temporal lobe epilepsy (MTLE) with isolated auras makes any difference in the clinical picture in comparison with MTLE in which only complex partial seizures (CPS) occur. We included 100 patients (aged 16–59 years) with unilateral medial temporal lobe lesions who consecutively underwent presurgical evaluation due to intractable MTLE and who became completely aura- and seizure-free after the anterior temporal resection. Preoperatively, isolated auras were present in 70 patients. These patients were categorised into the IA group. The remaining 30 patients in whom the auras preceded seizures were categorised into the NIA group. We found no difference between the two groups for the age at onset, epilepsy duration or aura types. Conversely, a right-sided epileptogenic region (61%) occurred more frequently in the IA group than in the NIA group (27%, P = 0.001). Conclusively, isolated auras show affinity to the right hemisphere. One explanation may be that seizures stop more quickly in the right hemisphere. Another hypothesis is that consciousness can be disturbed much easier by the ictal activity in left temporal seizures: auras evolve more frequently to CPS due to the disturbance of consciousness. © 2003 BEA Trading Ltd. Published by Elsevier Ltd. All rights reserved. Key words: simple partial seizures; lateralisation; mesial temporal lobe epilepsy; isolated aura; right hemisphere.

INTRODUCTION

METHODS

Medial temporal lobe epilepsy (MTLE) is characterised by complex partial seizures (CPS) and auras. Auras can occur independent of the CPS in 74% of patients with MTLE1 . It is unknown why in most patients some auras do not evolve to the complex partial phase, while in others auras are always followed by CPS. The understanding of the mechanism of isolated auras has also therapeutic implications. Aura intervention, such as a voluntary interruption of the evolution of the aura to the complex partial phase, may be beneficial to some patients. About 10% of patients with epilepsy report that they can successfully inhibit their CPS in the presence of auras or prodromas2 . This can also be a learned technique leading to significant reduction of disabling seizures. The aim of our study is to analyse whether MTLE with isolated auras makes any difference in the clinical picture in comparison with MTLE in which only CPS occur.

In this retrospective study, we included all patients with intractable MTLE due to medial temporal lobe lesions who consecutively underwent presurgical evaluation, including non-invasive video-EEG monitoring with seizure registration from 1993 to 2001 and who became aura- and seizure-free after the anterior temporal resection (category Engel Ia). Patients without aura experience were excluded. The postsurgical outcome was assessed 2 years after the surgery. The data on the age at epilepsy onset, usual seizure frequency, and presence of generalised tonic–clonic seizures were derived from medical records registered at our centre. At the admission to the presurgical unit, all patients were asked about the nature of their auras and whether they had auras which were not followed by disabling seizures. We defined an aura as a subjective phenomenon immediately preceding the CPS. Sometimes auras without proceeding CPS also occurred. These cases were defined as isolated auras. Because all patients had

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drug-resistant CPS, even patients in whom isolated auras occurred also had non-isolated auras. We categorised the auras according to their nature into abdominal, affective, dysmnestic, olfactory, gustatory, somatosensory, auditory, vertigo and non-specific auras.

cavernoma and focal cortical dysplasia occurred in 1 patient each. Table 1 shows the clinical features of the IA and NIA groups. Right-sided epileptogenic regions (61%) occurred more frequently in the IA group than in the NIA group (27%, P = 0.001). Thus, 84% of patients with a right-sided mesiotemporal epileptogenic region had isolated auras, while they occurred in only 55% of patients with a left-sided mesiotemporal region. The type of aura showed no difference between the two groups (see Table 2). The Wada test was necessary in 60% of patients to establish speech and memory lateralisation. The speech dominance could not be determined in two patients. Concerning the remaining 58 patients, isolated auras occurred in 81% of patients with non-dominant epileptogenic regions, while they occurred in 58% of patients having dominant epileptic foci (P = 0.05).

Statistical methods For the analysis of the categorical data, Chi-square or Fisher’s exact tests were carried out. For continuous variables, the Mann–Whitney test was used. Two-tailed error probabilities smaller than P < 0.05 were considered to be significant.

RESULTS There were 100 patients who met the inclusion criteria. Isolated auras were present in 70 patients, whom we categorised them into the IA group, while the remaining 30 patients, in whom the aura always occurred before the seizures, were categorised into the NIA group. The mean age of patients was 31.4 years (range 16–59). There were 54 women and 46 men. The mean age at epilepsy onset was 11.9 years (range 1–37). In 51 patients, the epileptogenic region was on the right, while in 49 patients it was on the left side. All patients had CPS proved by ictal video-EEG. All of them showed unilateral medial temporal lobe lesions on the preoperative MRI. The histopathological examination revealed hippocampal sclerosis in 80, ganglioglioma in 12, other low-grade tumours in 6 cases, while a

DISCUSSION Our main results are that isolated auras show an affinity to the right (or non-dominant) hemisphere, whereas neither the aura type nor the clinical history differentiate between NIA and IA groups. For the right-sided predominance of isolated auras, we can offer two hypotheses. An ictal seizure pattern is frequently absent during the auras compared to the pattern during CPS even in the same patient1 , suggesting that the seizure activity involves only a small volume of brain tissue, thus, the ictal activity does not reach the EEG electrodes. A SPECT study revealed that the isolated auras

Table 1: General data and clinical history of patients with or without isolated auras. All patients (N = 100)

NIA group (N = 30)

IA group (N = 70)

P value

11.9 ± 8 19.4 ± 11 46 51 82 49

13.3 ± 7 17.3 ± 8 17 (57%) 8 (27%) 26 (87%) 16 (53%)

11.3 ± 8 20.4 ± 12 29 (41%) 43 (61%) 56 (80%) 33 (47%)

0.1 0.3 0.16 0.001 0.4 0.66

(year)a

Age at onset Duration of epilepsy (year)a Men Right-sided epileptogenic region More than 1 seizure/month Presence of generalised tonic–clonic seizures a

Mean ± SD.

Table 2: Aura types in patients with or without isolated auras.

Abdominal aura Dysmnestic aura Affective aura Olfactory aura Auditory aura Somatosensory aura Vertigo Gustatoric aura

All patients (N = 100)

NIA group (N = 30)

69 15 25 5 3 6 6 1

20 (67%) 5 (17%) 5 (17%) 3 (10%) 2 (7%) 0 (0%) 3 (10%) 0 (0%)

IA group (N = 70) 49 10 20 2 1 6 3 1

(70%) (14%) (28%) (3%) (1%) (9%) (4%) (1%)

P value 0.81 0.77 0.2 0.16 0.21 0.17 0.36 1.0

Isolated auras in medial temporal lobe epilepsy

are associated with seizure activity not extending to the temporal lobes3 . Thus, one explanation for our results is that the seizure activity remains more localised or stops more quickly in the right hemisphere than in the left hemisphere. Indeed, PET hypometabolism is more restricted to the mesiotemporal region in the right-sided MTLE than in left-sided MTLE4 . In the current seizure classification, impaired consciousness is the key feature in the distinction between simple and complex partial seizures. Thus, one can speculate that in simple partial seizures (auras), the brain structures responsible for maintaining consciousness are not affected by the ictal disturbance. Automatisms with preserved consciousness occur almost exclusively in non-dominant temporal seizures, while ictal unconsciousness appears much more often during left-sided seizure activity5 . We can hypothesise that in left temporal seizures consciousness can be disturbed much easier by the ictal activity, auras change more frequently to CPS due to the disturbance of consciousness. All patients had intractable epilepsy in this study, so it is unknown whether those MTLE patients who had only auras and no CPS at all had right-sided epilepsy more often. If this is the case, one can speculate that most of those patients who have only auras and have never experienced intractable seizures do not seek medical help: their epilepsy remains unrecognised.

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This speculation could explain why left-sided epilepsy occurs more often than the right-sided disorders6 . ACKNOWLEDGEMENTS This work was supported by a grant from the Deutsche Forschungsgemeinschaft (DFG-Eb 111/2-2) and from the Humboldt Stiftung (Dr Janszky).

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