Felipe Quesney

Excitatory amino acids are elevated in human epileptic cerebral cortex

We used intraoperative electrocorticography to identify and compare specimens from two groups of patients undergoing temporal lobectomy: (1) spiking cortex (12 patients)—epileptic activity recorded over much of the temporal convexity; and (2) nonspiking cortex (9 patients)—temporal convexity free of interictal spiking, epileptic activity confined to the hippocampus and/or amygdala. Comparative amino acid levels were (μmol/g protein, mean ±: SEM): glutamate—spiking 109.8 ±: 1.8, nonspiking 87.4 ±: 2.0 (p < 0.001); aspartate—spiking 15.2 ±: 0.9, nonspiking 12.2 ±: 0.5 (p < 0.05); GABA—spiking 15.0 ±: 1.0, nonspiking 13.9 ±: 1.4 (NS); taurine—spiking 14.5 ±: 0.8, nonspiking 12.2 ±: 0.8 (NS); and glycine—spiking 11.5 ±: 0.8, nonspiking 7.4 ±: 0.6 (p < 0.01). Cortical epileptic activity appears to be associated with elevated concentrations of glutamate, aspartate, and glycine, but not GABA and taurine, perhaps indicating a relative imbalance between putative excitatory and inhibitory amino acid neurotransmitters.

Does head‐turning during a seizure have lateralizing or localizing significance?

Forced lateralized head-turning, occurring as the first clinical sign in 106 epileptic seizures in 43 patients, was recorded on videotape simultaneously with the EEG. Forty-five ictal EEGs were obtained with stereotaxically implanted intracerebral electrodes. Forced head-turning was seen with seizures that had a frontal, temporal, unilateral diffuse, or a generalized onset in the EEG. Ipsilateral was as common as contralateral head-turning in all groups, including the seizures with frontal lobe onset. Initial head-turning in a seizure has no localizing or lateralizing significance.

Electrocorticography and outcome in frontal lobe epilepsy

The prognostic significance of epileptiform activity (EA) recorded at electrocorticography (ECOG) was examined in a group of 60 consecutive non-tumoral patients with intractable frontal lobe epilepsy (FLE). Pre-excision EA was documented as absent, focal (one gyrus), regional (two gyri), lobar (3 gyri) or multilobar (frontal + temporal gyri). Post-excision EA was documented as absent, restricted to the resection border, or recorded distant to the resection border, and was quantitated by spike frequency. Pre-excision EA from < or = 2 gyri and absence of post-resection EA correlated with Class I or II (Engel classification) outcome while pre-excision EA from > or = 3 gyri and persistent post-resection EA, especially distant to the resection border, correlated with Class III or IV outcome (P < 0.001). A significant correlation between poorer outcomes and increased abundance of distant post-resection EA was observed (P < 0.001). EA restricted to the resection border was not significantly correlated with outcome. Presence of a circumscribed lesion correlated with Class I outcome (P < 0.01) and absence of pathological abnormality correlated with Class IV outcome (P < 0.05). Neither side nor extent of surgical excision correlated with outcome. EA recorded at ECOG is of prognostic significance in FLE. A lobar or multilobar distribution of pre-excision EA and persistent post-excision EA distant to the resection border, especially when abundant, are highly unfavorable prognostic indicators. In contrast, a restricted distribution of pre-excision EA and absence of post-resection EA both herald a favorable outcome.

The indications for and the role of depth electrode recording in epilepsy

A series of 47 patients studied with stereotactically implanted depth electrodes is analyzed. Indications and grouping of the patients fall into three main categories: (a) the bitemporal series (35 patients) where there is ambiguity as to the lateralization of the focus; (b) the unilateral series (6 patients) where the problem is one of localization within one hemisphere, and (c) the generalized series where one tries to determine the primary focus in secondary generalized seizures (6 patients). The best indication appears to be the bitemporal cases, in which a large number of attacks can be recorded by computer. Most of them tend to have a well-lateralized onset in one of the temporal lobes; 32 of the 35 implanted patients were operated upon (91.4%). The results on the seizure tendency in these patients is comparable, if not superior, to those obtained in the so-called unilateral cases. Correlation studies indicate that interictal activity is a good indicator of the predominance of seizures.

Enzyme changes in actively spiking areas of human epileptic cerebral cortex

Five enzymes involved in glutamic acid, GABA, and catecholamine metabolism were measured in epileptic human brain. Electrocorticographically defined areas of focal spiking were compared with samples from surrounding nonspiking cortex. Comparative enzyme activities were as follows (μmol/h/g wet wt): glutamic acid dehydrogenase (GDH)-spiking 135.77 ± 10.22 (mean ± SEM), nonspikingll8.58 ± 9.42 (p < 0.001, N = 17); gluotamicacid decarboxylase—spiking 10.63 ± 0.95, nonspiking 9.96 ± 1.10 (NS, N = 13); GABA-aminotransferase—spiking 36.49 ± 1.05, nonspiking 36.46 ± 1.48 (NS, N = 12); glutamine synthetase-spiking 96.94 ± 3.81, nonspiking 96.52 ± 4.10 (NS, N = 20); and tyrosine hydroxylase (TH; nmol/h/g)-spiking 16.23 ± 2.39, nonspiking 10.67 ± 1.95 (p < 0.001, N = 14). Increased activity of GDH and TH may prove useful to characterize further areas of active spiking in human focal epilepsy.

Morbidity of chronic recording with intracranial depth electrodes in 170 patients.

A consecutive series of 170 patients who have been submitted to intracranial depth electrode recordings is reviewed to assess the overall morbidity of the technique. Most patients had bitemporal and frontal electrodes inserted and were monitored for an average period of 18 days. A surgically amenable focus was found in 85% of the cases. There were 4 cases of infection including 2 cerebral abscesses which required surgical evacuation. One patient with frontal lobe atrophy developed an acute subdural hematoma after electrode implantation. There was no death or neurological deficit in the entire series. Morbidity was encountered mainly in the neuropsychological sphere, several patients having developed transient postictal psychosis after repetitive seizures. Our recording technique has been associated with low surgical morbidity. Patients undergoing depth electrode recordings should be closely monitored to minimize the occurrence of psychotic episodes associated with drug withdrawal and increased seizure frequency.

Induction of burst-suppression and activation of epileptiform activity after methohexital and selective amygdalo-hippocampectomy

Electrocorticography (ECOG) compared the effects of methohexital (MTH) and selective amygdalo-hippocampectomy (selAH) upon lateral temporal neocortical epileptiform activity (EA) in 31 patients with mesial temporal epilepsy. Pre-excision ECOG showed independent neocortical EA before MTH in 12/31 and after MTH in 18/31. MTH (20-50 mg) activated neocortical EA in 12 cases and induced burst-suppression (BS) over temporal neocortex in 14/31. Post-excision ECOG showed neocortical EA in 21/31 and BS in 27/31: compared with pre-excision ECOG before MTH, selAH activated neocortical EA in 15 cases. Significant correlations were found between presence of pre-excisional neocortical EA and presence of post-excisional neocortical EA (P < 0.001) and between activation of pre-excisional neocortical EA by MTH and activation of (post-excisional) neocortical EA by selAH (P < 0.006). Presence or severity of BS in the post-excision ECOG was not correlated with presence, absence or activation of post-excisional EA. Presence of neocortical EA was significantly correlated with a higher pre-operative seizure frequency (P < 0.001) but not with duration of epilepsy nor surgical outcome. Both MTH and selAH can induce neocortical BS, likely through chemical and surgical disconnection of cortex, respectively. Unrelated to induction of BS, MTH and selAH appear to decrease threshold for expression of neocortical EA in a similar fashion.