Value of non-invasive testing when there are independent bitemporal seizures in the scalp EEG

Kindling in humans: Does secondary epileptogenesis occur?

The relevance of secondary epileptogenesis for human epilepsy remains a controversial subject decades after it was first described in animal models. Whether or not a previously normal brain region can become independently epileptogenic through a kindling-like process has not, and cannot, be definitely proven in humans. Rather than reliance on direct experimental evidence, attempts to answering this question must depend on observational data. In this review, observations based largely upon contemporary surgical series will advance the case for secondary epileptogenesis in humans. As will be argued, hypothalamic hamartoma-related epilepsy provides the strongest case for this process; all the stages of secondary epileptogenesis can be observed. Hippocampal sclerosis (HS) is another pathology where the question of secondary epileptogenesis frequently arises, and observations from bitemporal and dual pathology series are explored. The verdict here is far more difficult to reach, in large part because of the scarcity of longitudinal cohorts; moreover, recent experimental data have challenged the claim that HS is acquired consequent to recurrent seizures. Synaptic plasticity more than seizure-induced neuronal injury is the likely mechanism of secondary epileptogenesis. Postoperative running-down phenomenon provides the best evidence that a kindling-like process occurs in some patients, evidenced by its reversal. Finally, a network perspective of secondary epileptogenesis is considered, as well as the possible role for subcortical surgical interventions.

Diagnosis and Surgical Treatment of Drug-Resistant Epilepsy

Despite appropriate trials of at least two antiepileptic drugs, about a third of patients with epilepsy remain drug resistant (intractable; refractory). Epilepsy surgery offers a potential cure or significant improvement to those with focal onset drug-resistant seizures. Unfortunately, epilepsy surgery is still underutilized which might be in part because of the complexity of presurgical evaluation. This process includes classifying the seizure type, lateralizing and localizing the seizure onset focus (epileptogenic zone), confirming the safety of the prospective brain surgery in terms of potential neurocognitive deficits (language and memory functions), before devising a surgical plan. Each one of the above steps requires special tests. In this paper, we have reviewed the process of presurgical evaluation in patients with drug-resistant focal onset epilepsy.

Techniques for placement of grid and strip electrodes for intracranial epilepsy surgery monitoring: Pearls and pitfalls

BACKGROUND

Placement of intracranial strip and grid electrodes for recording cortical electrocorticography is important as part of the workup of patients who are being considered for resective epilepsy surgery. In recent decades, the indications and techniques for intracranial epilepsy monitoring have been refined.

METHODS

In this article, the authors describe the techniques for intraoperative placement of grid and strip electrodes for extraoperative study of a seizure focus.

RESULTS

Methods to enhance the efficacy of this technique while minimizing complications are reviewed.

CONCLUSIONS

Intracranial epilepsy monitoring with grid and strip electrodes is a useful tool for the planning of resective epilepsy surgery. Techniques to advance the safety and minimize complications will lead to improved outcomes.

Temporolimbic activation by intracranial electrical stimulation

BACKGROUND

To evaluate the results of intracranial electrical stimulation (ICES) as a pre-surgical tool in order to select the side of the operation in bitemporal lobe epilepsy (BTLE) patients who underwent depth electrode (DE) implantation.

METHODS

We reviewed the files of 77 medically intractable BTLE patients who underwent ICES with positive results through implanted DEs and then were under surgical treatment. One year or more after surgery, we evaluated the outcome. ICES was performed through: 1) Square-wave bipolar stimulation with symmetrical pulses of 60 Hz for 0.5 ms was delivered by a constant current Nuclear Chicago stimulator; 2) An initial intensity of 0.5 mA, and subsequently progressively stronger currents at 1-2 and occasionally 3 or 4 mA; 3) The duration of a single stimulation was usually 5 seconds; 4) The volume of tissue effectively stimulated did not exceed 5 mm.

RESULTS

We obtained habitual auras or seizures (clinical responses, CRs) in 74 patients and after-discharges, ADs in 61 of them, according to Engel's classification for post surgery outcomes. If CRs or ADs were obtained by stimulation of only one temporal lobe the result of epilepsy surgery tended to be better (Engel classes I or II) when the operation was done on the same side of positive CRs (15 cases) or ADs (14 cases), and tended to be worse (Engel classes III or IV) when the ICES had provoked bilateral responses or when the side operated on was contra-lateral to positive CRs (33 cases) or ADs (28 cases). Statistical analyses were performed in order to test these results and we found better post-operative results when the resection took place in the same side of positive responses to ICES (CRs: chi2 4.74 and p=0.0295; ADs: chi2 7.57 and p=0.0059).

CONCLUSION

In addition to other methods (PET, MRI and neuropsychology) presurgical ICES can provide useful data in the process of identifying the temporal lobe to be targeted for resection in BTLE patients.