Seizure: European Journal of Epilepsy
Volume 19, Issue 5 , Pages 261-263, June 2010

The duration of temporal lobe epilepsy and seizure outcome after epilepsy surgery

  • Natalie Marie Lowe

      Affiliations

    • Salford Royal Foundation Trust, Stott Lane, Salford, Lancashire M6 8HD, United Kingdom
    • Corresponding Author InformationCorresponding author. Tel.: +44 07954604717.
    • ,
  • Paul Eldridge

      Affiliations

    • The Walton Centre NHS Foundation Trust, Lower Lane, Fazakerley, Liverpool, Merseyside, L9 7LJ, United Kingdom
    • ,
  • Thelekat Varma

      Affiliations

    • The Walton Centre NHS Foundation Trust, Lower Lane, Fazakerley, Liverpool, Merseyside, L9 7LJ, United Kingdom
    • ,
  • Udo C. Wieshmann

      Affiliations

    • The Walton Centre NHS Foundation Trust, Lower Lane, Fazakerley, Liverpool, Merseyside, L9 7LJ, United Kingdom

Received 9 November 2009; accepted 26 February 2010. published online 30 April 2010.

Article Outline

Abstract 

To assess the effect of the duration of epilepsy on the outcome of epilepsy surgery in non-lesional medically refractory temporal lobe epilepsy we reviewed the outcome of 76 patients.

Methods

All patients had anterior temporal resections for “non-lesional” temporal epilepsy (excluding any patient with tumours or vascular malformations but including patients with hippocampal sclerosis). Outcome at one year was assessed using Engel's scale.

Results

67% had a good outcome (Engel I or II). The mean duration of epilepsy was 23.0 years (range 2.9–46.9 years). Overall, there was no significant difference between patients with good outcome (mean duration 22.4 years) and poor outcome (mean duration 24.2 years) (p=0.49). The proportion of patients with good outcome was slightly higher in the shorter duration groups. (Duration less than 10 years 75%, 10–19 years 71%, 20–29 years 65%, 30–39 years 62%, and 40–49 years 60% good outcome, p=0.95).

Conclusion

We found no significant associations between outcome and duration of epilepsy.

Keywords: Epilepsy, Surgery, Temporal lobectomy, Duration

 

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1. Introduction 

Mesiotemporal lobe epilepsy is often refractory to medical treatment but epilepsy surgery can be extremely effective.1

However, a substantial number of patients continue to have seizures, with the number of patients remaining seizure free decreasing over the years to as low as 38%.2

The reasons for failure are poorly understood. A plausible hypothesis is that ongoing seizure activity causes an epileptogenic kindling process3 resulting in new epileptic “mirror” foci.4

The longer the epilepsy the higher the risk of mirror foci and the lower that chance to be seizure free after epilepsy surgery. Hence the duration of epilepsy should be an important (negative) predictor of outcome in epilepsy surgery. The aim of our study was to determine if there was a link between outcome and duration.

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2. Methods 

The study was registered and conducted as an audit at the Walton Centre and our local ethical committee was informed about the study and has approved the study.

Data from patients with mesial temporal lobe epilepsy, operated on between 1992 and 2005 at the Walton Centre for Neurology and Neurosurgery (WCNN) were collected.

Patients with mesiotemporal temporal lobe epilepsy who were investigated and operated on between 1996 and 2004 were reviewed. All patients who had tumours, vascular lesions such as cavernous haemangiomas or selective amygdalohippocampectomies were excluded to reduce the possibility of confounding factors, leaving only patient who had anterior temporal lobectomies for non-lesional epilepsy for analysis. Seventy-six patients were included. Histological examination showed hippocampal sclerosis or gliosis. All patients underwent a standardised presurgical work-up including EEG, neuropsychology, magnetic resonance imaging (MRI) including quantitative measurements of the hippocampal volume and T2 relaxation time5 and Sodium Amytal (WADA) test.6 In patients in whom the seizure onset could not be localized with scalp EEG, invasive EEG with foramen ovale electrodes was used7, 8 or invasive EEGs performed.

Postsurgical MR imaging in all patients who were not seizure free showed that the intended structures were resected.

Outcome data for at one year postoperatively was classified using Engel's classification (Ia=seizure free, Ib=auras only, II=rare seizures (not more than 2 per year), III=worthwhile improvement (reduction of seizures of 90% or more), IVa=significant reduction, IVb=unchanged, IVc=worse).9 Patients falling into the various subgroups of Engel's class II and III were pooled.

We used Engel's classification because this classification is most widely used. The International League against Epilepsy (ILAE) recently suggested a revision of the classification.10 For the purpose of our study Engel 1a=ILAE 1, Engel 1b=ILAE 2. ILAE categories 4 and 5 cover a wide range of outcomes. For example outcome 5=less than 50% reduction to 100% increase. In our study a 50% decrease was classified as Engel IVa and a 100% increase as Engel IVc.

The outcome of the surgery, categorised into Engel's classification criteria, was collected independently and blindly (i.e. with no suggestion when collecting the information as to what it was to be analysed for).

Chi squared test and t-tests were used to identify any significant differences.

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3. Results 

Overall 67% were seizure free or “almost seizure free” one year after surgery (Engel Ia, Ib-d, II,III,IV/28,18,5,3,22). The mean duration of epilepsy was 23.0 years (range 2.9–46.9 years). The frequency chart produced for the duration of epilepsy showed a relatively good spread of durations (Fig. 1). On the other hand the patients were more homogenous in terms of age of onset (Fig. 2).

Overall, there was no significant difference between patients with good outcome (mean duration 22.4 years) and poor outcome (mean duration 24.2 years) (p=0.49). The proportion of patients with good outcome was slightly higher in the shorter duration groups (Fig. 3). (Duration less than 10 years 75%, 10–19 years 71%, 20–29 years 65%, 30–39 years 62%, and 40–49 years 60% good outcome, p=0.95). Table 1 shows clinical, EEG and MRI findings.

Table 1. Clinical, EEG and MRI data in different duration groups. OP=operation (anterior temporal lobectomy), FC=history of prolonged and/or complicated febrile convulsions, sEEG=surface EEG, inEEG=invasive EEG with foramen ovale electrodes or depth electrodes.
Duration [years]Number of patientsMean age at OP [years]FCSEEG/inEEGHippocampal asymmetry on MRIOutcome Engel I+II
<10 years828.122146
10–192429.6096 (2 depth)1217
20–292633.769101917
30–391342.086698
40–49548.772153

The oldest patient was 53 years old at the time of operation. He had suffered from epilepsy since the age of 10 years. Epilepsy surgery was first considered at the age of 22 years at another hospital in 1967. He had one postoperative seizure but remained seizure free thereafter.

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4. Discussion 

In our study the duration that a patient has had temporal lobe epilepsy, did not have an effect on the outcome of their subsequent surgery. We found a trend for a better outcome in patients with shorter duration but this was not significant. Possible confounding factors such as lesions11 and the use of different types of surgery12 were excluded. Patient selection and presurgical investigations were standardised. The outcome of the surgery, categorised into Engel's classification criteria, was collected independently and blindly (i.e. with no suggestion when collecting the information as to what it was to be analysed for), to decrease information collection bias.

Our study is in keeping with the results of most other studies, which failed to find a link between the duration of epilepsy and outcome.13, 14 We used the outcome one year after surgery, because one-year outcome is usually considered as a good predictor of long-term outcome15, 16 but our study does not allow conclusions regarding the long term. In one study the duration of epilepsy affected the long-term (five years) outcome.17 It is unclear why patients with a longer duration of epilepsy only relapsed at a later state and one difficulty in this study was that an increasing number of patients were lost in the longer follow-up assessments. Long-term outcome was not affected by the duration of epilepsy in another large study.18

Patients who suffered from epilepsy for a long time may have more difficulties to adjust and there is a higher risk of side effects including cognitive side effects of epilepsy surgery in older patients19 but some older patients can have an excellent outcome. This result is important when determining whether a candidate should be offered surgery.

While our data did not support the existence of an ongoing epileptogenic process, at least not in our patient population, a kindling process cannot be entirely excluded. Kindling may not only be related to the duration of epilepsy but also to the frequency of seizures and the frequency of secondary generalisation. Furthermore, frequent subclinical events may also trigger a kindling process.

Nevertheless, from a practical point of view a long duration of epilepsy alone should not be used as an exclusion criterion for epilepsy surgery.

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Appendix A. Supplementary data 

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References 

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PII: S1059-1311(10)00054-3

doi:10.1016/j.seizure.2010.02.011

Seizure: European Journal of Epilepsy
Volume 19, Issue 5 , Pages 261-263, June 2010

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