The implantation effect: delay in seizure occurrence with implantation of intracranial electrodes.

OBJECTIVE: A transient decrease in seizure frequency has been identified during therapeutic brain stimulation trials with stimulator in patients in the inactive sham group. This study was performed to examine whether the implantation of intracranial electrodes decreases seizure occurrence and explores factors that may be associated. METHODS: A retrospective review of 193 patients was performed, all evaluated with both scalp video EEG monitoring and intracranial EEG (iEEG) monitoring. Data about the number of seizures per day during the monitoring period, the number of days until the first seizure, anti-epileptic drugs (AEDs), pain medications, types of implanted electrodes, and anesthetic agents were reviewed. We conducted a repeated measure analysis for counted data using generalized estimating equations with a log-link function and adjustment for number of days and anti-epileptic medication load on the previous day to compare seizure frequencies between scalp and iEEG monitoring. RESULTS: The time to the first seizure was significantly prolonged during iEEG monitoring as compared to scalp monitoring after correction for AED withdrawal (hazard ratio: 0.81, CI 0.69-0.96). During scalp video EEG monitoring, patients experienced an average of 1.09 seizures/day vs 1.27 seizures/day during iEEG monitoring (P=.066). There was no significant difference in seizure frequency in patients that received craniotomy vs burr holes only for intracranial implantation. An increasing number of electrodes implanted increased the delay to seizures (P=.01). Of all anesthetic agents used, desflurane seemed to have an anticonvulsive effect compared to other anesthetics (P=.006). Pain medication did not influence delay to seizures. SIGNIFICANCE: Seizures are delayed during iEEG as opposed to scalp monitoring illustrating the "implantation effect" previously observed. Surgical planning should account for longer monitoring periods, particularly when using larger intracranial arrays.

Secondarily generalized seizures in mesial temporal epilepsy: clinical characteristics, lateralizing signs, and association with sleep-wake cycle.

PURPOSE: Secondarily generalized seizures (SGSs) are often considered to be stereotyped, presumably sharing a common electrical pathway. We examined whether SGSs are uniform in a homogeneous group of patients with mesial temporal epilepsy, and whether certain clinical signs associated with generalization are lateralizing with regard to seizure origin. METHODS: A comprehensive, standardized video/EEG analysis was performed of the clinical characteristics of 29 patients (69 SGSs) with mesial temporal seizure onset. RESULTS: The sequence of tonic postures, as well as the sequence of tonic and clonic activity, was variable in SGSs of mesial temporal origin. The sequence of tonic activity, followed by vibratory and then clonic activity alone, was seen only in 51.7% of patients. Tonic and clonic activity could occur simultaneously. The most common clinical signs were forced head deviation (89.7%) and vocalization (75.9%). The most common tonic posture was bilateral arm extension (72.4%). All other clinical signs occurred in <60% of patients. Among these, early forced head deviation, asymmetric tonic facial contraction, tonic arm abduction with elbow flexion, and tonic arm extension combined with opposite arm flexion had lateralizing significance. The preceding partial seizure in SGSs (mean, 43.6 s) was significantly shorter than partial seizures without generalization (mean, 105.2 s; p < 0.001). SGSs occurred more often out of sleep (p < 0.01). CONCLUSION: Secondarily generalized seizures of mesial temporal origin are not uniform in their clinical presentation. The final phases of SGSs are more stereotyped than the initial clinical signs of generalization. This suggests variable electrical spread patterns, which may end in a common pathway. Some asymmetric motor signs have lateralizing significance. SGSs were associated with sleep and abbreviated partial seizures.

Medically intractable, localization-related epilepsy with normal MRI: presurgical evaluation and surgical outcome in 43 patients.

PURPOSE: High-resolution magnetic resonance imaging (MRI) plays a crucial role in the presurgical evaluation of patients with medically refractory partial epilepsy. Although MRI detects a morphologic abnormality as the cause of the epilepsy in the majority of patients, some patients have a normal MRI. This study was undertaken to explore the hypothesis that in patients with normal MRI, invasive monitoring can lead to localization of the seizure-onset zone and successful epilepsy surgery. METHODS: A series of 115 patients with partial epilepsy who had undergone intracranial electrode evaluation (subdural strip, subdural grid, and/or depth electrodes) between February 1992 and February 1999 was analyzed retrospectively. Of these, 43 patients (37%) had a normal MRI. RESULTS: Invasive monitoring detected a focal seizure onset in 25 (58%) patients, multifocal seizure origin in 12 (28%) patients, and in six patients, no focal seizure origin was found. Of the 25 patients with a focal seizure origin, cortical resection was performed in 24, of whom 20 (83%) had a good surgical outcome with respect to seizure control. Six of the 12 patients with multifocal seizure origin underwent other forms of epilepsy surgery (palliative cortical resection in two, anterior callosotomy in two, and vagal nerve stimulator placement in two). CONCLUSIONS: Successful epilepsy surgery is possible in patients with normal MRIs, but appropriate presurgical evaluations are necessary. In patients with evidence of multifocal seizure origin during noninvasive evaluation, invasive monitoring should generally be avoided.

Cryptogenic epilepsy: an infectious etiology?

PURPOSE: Cryptogenic epilepsy, the group of epilepsy syndromes for which an etiology is unknown, comprises approximately 20% of all epilepsy syndromes. We selected patients in this subgroup of epilepsy and tested them for evidence of Toxoplasma gondii IgG antibodies by the enzyme-linked immunosorbent assay. T. gondii is found in up to 20% of the U.S. population forming dormant brain cysts in the latent bradyzoite form. We investigated the hypothesis that dormant T. gondii infection might be associated with cryptogenic epilepsy. METHODS: We selected patients with cryptogenic epilepsies and tested them for evidence of T. gondii IgG antibodies by the enzyme-linked immunosorbent assay. A control group was also tested for comparison. RESULTS: We have found a statistically-significant elevation of T. gondii antibodies among cryptogenic epilepsy patients as compared to controls [59% increase in optical density (OD), p = 0.013]. This association persisted after adjustment for subjects' gender and age in a multiple logistic regression model; however, it was no longer as statistically significant. CONCLUSIONS: Our results suggest that chronic T. gondii infection with brain cysts may be a cause of cryptogenic epilepsy.

Investigation of extra-temporal epilepsy.

Medically intractable epilepsy of extra-temporal origin can represent a difficult therapeutic challenge. Our Epilepsy Service has managed these patients using standard investigative methods as well as ictal SPECT and intracranial electrode recording. In the present series of patients, image-guided surgery was used for all electrode implantation and resective surgery. Seizure localization and successful resection were achieved in 70-80% of 42 patients with follow-up of at least one year. Normal MRI and previous failed intracranial investigation were not associated with poorer outcome.

Does performing image registration and subtraction in ictal brain SPECT help localize neocortical seizures?

UNLABELLED: Ictal brain SPECT (IS) findings in neocortical epilepsy (patients without mesiotemporal sclerosis) can be subtle. This study is aimed at assessing how the seizure focus identification was improved by the inclusion of individual IS and interictal brain SPECT (ITS)-MRI image registration as well as performing IS - ITS image subtraction. METHODS: The study involved the posthoc analysis of 64 IS scans using 99mTc-ethyl cysteinate dimer that were obtained in 38 patients without mesiotemporal sclerosis but with or without other abnormalities on MRI. Radiotracer injection occurred during video-electroencephalographic (EEG) monitoring. Patients were injected 2-80 s (median time, 13 s) after clinical or EEG seizure onset. All patients had sufficient follow-up to correlate findings with the SPECT results. All patients had ITS and MRI, including a coronal volume sequence used for registration. Image registration (IS and ITS to MRI) was performed using automated software. After normalization, IS - ITS subtraction was performed. The IS, ITS, and subtraction studies were read by 2 experienced observers who were unaware of the clinical data and who assessed the presence and localization of an identifiable seizure focus before and after image registration and subtraction. Correlation was made with video-EEG (surface and invasive) and clinical and surgical follow-up. RESULTS: Probable or definite foci were identified in 38 (59%) studies in 33 (87%) patients. In 52% of the studies, the image registration aided localization, and in 58% the subtraction images contributed additional information. In 9%, the subtraction images confused the interpretation. In follow-up after surgery, intracranial EEG or video-EEG monitoring (or both) has confirmed close or reasonable localization in 28 (74%) patients. In 6 (16%) patients, SPECT indicated false seizure localization. CONCLUSION: Image registration and image subtraction improve the localization of neocortical seizure foci using IS, but close correlation with the original images is required. False localizations occur in a minority of patients.

Intractable seizures of frontal lobe origin: clinical characteristics, localizing signs, and results of surgery.

PURPOSE: We analyzed the clinical characteristics of seizures of frontal lobe (FL) origin with particular emphasis on establishing different categories and determining if these categories had any localizing or lateralizing value. In addition, results of surgery are reported. METHODS: Seizure characteristics were established by historical review and electroencephalographic/videotape analysis of 449 seizures in 26 adult patients with refractory seizures of FL origin. RESULTS: No outstanding risk factor was identified for seizures of FL origin. Seizures were frequent (7.1 per week), brief (mean duration, 48.3 seconds), and had a nocturnal preponderance in 58% of the patients. Status epilepticus was reported in 54%, and generalized convulsions as a prominent seizure type were reported in 26% of patients. The most common reported aura was a nonspecific sensation, often localized to the head (35%). Early forced head and eye deviation was not a consistent lateralizing sign, whereas late head and eye deviation always occurred contralateral to the site of seizure origin. Early asymmetric tonic posturing occurred consistently contralateral to the side of seizure origin. Clinical seizure patterns did not consistently localize to specific regions of the frontal lobe, although there were some noticeable trends: focal clonic seizures were associated with seizure origin in the frontal convexity; tonic seizures were most often associated with origin in the supplementary motor area but also occurred with origin in other parts of the frontal lobe; seizures resembling typical temporal lobe seizures with oroalimentary automatisms were observed with seizure origin in the orbitofrontal region; and seizures with hyperactive, frenetic automatisms were not associated with any specific region within the frontal lobes. Eighty percent of patients had favorable seizure outcome after surgery (class I/II). CONCLUSION: Although certain clinical features are characteristic for seizures of frontal lobe origin and some have lateralizing value, they do not localize to specific areas within the FL. After careful presurgical evaluation, both lesional and nonlesional patients benefit from epilepsy surgery.

An unusual complication of intracranial electrodes.

This report describes two patients who developed persistent neurologic deficits during intracranial EEG recording without clear evidence of intracranial edema or infarction. Both patients had previously received high-dose brain radiation therapy and chemotherapy. Because of this experience, we strongly caution the use of intracranial electrodes in patients with similar profiles.

The role of intracranial electrode reevaluation in epilepsy patients after failed initial invasive monitoring.

PURPOSE: Intracranial electrode recording often provides localization of the site of seizure onset to allow epilepsy surgery. In patients whose invasive evaluation fails to localize seizure origin, the utility of further invasive monitoring is unknown. This study was undertaken to explore the hypothesis that a second intracranial investigation is selected patients warrants consideration and can lead to successful epilepsy surgery. METHODS: A series of 110 consecutive patients with partial epilepsy who had undergone intracranial electrode evaluation (by subdural strip, subdural grid, and/or depth electrodes) between February 1992 and October 1998 was retrospectively analyzed. Of these, failed localization of seizure origin was thought to be due to sampling error in 13 patients. Nine of these 13 patients underwent a second intracranial investigation. RESULTS: Reevaluation with intracranial electrodes resulted in satisfactory seizure-onset localization in seven of nine patients, and these seven had epilepsy surgery. Three frontal, two temporal, and one occipital resection as well as one multiple subpial transection were performed. Six patients have become seizure free, and one was not significantly improved. The mean follow-up is 2.8 years. There was no permanent morbidity. CONCLUSIONS: In selected patients in whom invasive monitoring fails to identify the site of seizure origin, reinvestigation with intracranial electrodes can achieve localization of the region of seizure onset and allow successful surgical treatment.

Localized pain associated with seizures originating in the parietal lobe.

PURPOSE: Ictal pain is a rare symptom of seizures. Epileptic pain may be experienced unilaterally (lateral/ peripheral), cephalically, or in the abdomen. Painful seizures have been associated with seizure origin in both the parietal and the temporal lobes. We report on the different types of epileptic pain and discuss its etiology and possible localizing value. METHODS: We reviewed the records of patients referred to our epilepsy program over the last 6 years. Eight (1.4%) of 573 patients had pain as an early prominent symptom of their seizures. RESULTS: Pain was predominantly unilateral in three patients, cephalic in two, and abdominal in three patients. Seizure onset was in or involving the parietal lobe in all patients, and when the painful symptoms were lateralized, they were contralateral to the side of seizure origin. Parietal lobe seizure origin was determined by both intracranial EEG recording and neuroimaging [magnetic resonance imaging (MRI), ictal single photon emission computed tomography (SPECT)] in five patients, and by both scalp EEG and neuroimaging in three patients. CONCLUSIONS: We conclude that ictal pain is a rare symptom of parietal lobe seizure origin with lateralizing potential.

Long-term seizure outcome following corpus callosotomy in children.

INTRODUCTION: The long-term outcome of pediatric patients undergoing corpus callosotomy (CC) for palliative control of medically intractable seizures is presented. METHODS: During a 27-year period, 43 patients, 20 years of age or younger, underwent CC for seizure palliation and had a minimum of 1 year follow-up. Seizure reduction and stability of that outcome for individual seizure types and for most disabling seizure were reviewed. RESULTS: Overall, 63% of the seizures documented showed a good response. For the most disabling seizure, 56% of the patients had good outcomes. Changes in outcome status occurred within the first 6 months, and outcome was largely maintained after that point. CONCLUSION: Callosotomy achieves the goal of seizure palliation in more than half of the patients, with stable, good outcomes being maintained in the majority of patients.

Six-month evaluation of Carbatrol (extended-release carbamazepine) in complex partial seizures.

We evaluated the use of a new, controlled-release capsule form of carbamazepine, Carbatrol capsules, in an open-label, multicenter study of 124 patients with complex partial seizures. Ninety-one percent of the patients successfully completed the 6-month trial with good seizure control, with a significant improvement in quality of life. We conclude that switching patients with complex partial seizures from multiple daily-dose carbamazepine to twice-daily Carbatrol on a milligram-to-milligram basis is relatively safe.

Medial temporal lobe epilepsy: videotape analysis of objective clinical seizure characteristics.

PURPOSE: The syndrome of temporal lobe epilepsy has been described in great detail. Here we focus specifically on the clinical manifestations of seizures originating in the hippocampus and surrounding mesial temporal structures. METHODS: Seizure origin was confirmed in 67 cases by depth EEG recording and surgical cure after mesial temporal resection. RESULTS: Among nonlateralized manifestations, we commonly found oral automatisms, pupillary dilatation, impaired consciousness, and generalized rigidity. Appendicular automatisms were often ipsilateral to the seizure focus, whereas dystonia and postictal hemiparesis were usually contralateral. Head deviation, when it occurred early in the seizure, was an ipsilateral finding, but was contralateral to the seizure focus when it occurred late. Clear ictal speech and quick recovery were found when seizures originated in the non-language-dominant hemisphere, but postictal aphasia and prolonged recovery time were characteristic of seizure origin in the language-dominant hemisphere. CONCLUSIONS: These signs help to define the mesial temporal lobe epilepsy (MTLE) syndrome and often provide information as to the side of seizure origin.

Successful epilepsy surgery without intracranial EEG recording: criteria for patient selection.

Twenty-two patients with intractable complex partial seizures (CPS) were treated with temporal lobectomy. Eighteen of 22 (82%) are seizure-free while receiving medication, with a mean follow-up time of 4 years. In each case, the clinical seizure pattern, interictal and ictal scalp EEG, magnetic resonance imaging (MRI), neuropsychological testing, and results of the intracarotid amobarbital procedure (IAP) converged to indicate a localized abnormality. None of the patients in this series had mass lesions, vascular malformations, or cortical scars, but 18 of 22 had hippocampal atrophy on MRI and 20 had hippocampal sclerosis (HS) on pathologic examination. We believe it is possible, on the basis of the preoperative evaluation described, to identify a population of epileptic patients who will do very well postoperatively. Such patients do not require invasive EEG monitoring, and they represent approximately 20% of the patients treated surgically in our epilepsy unit in the past several years.

Characteristics of medial temporal lobe epilepsy: I. Results of history and physical examination.

In order to more precisely define a syndrome of medial temporal lobe epilepsy, histories and physical findings were evaluated in 67 patients studied with intracranial electrodes who had medial temporal seizure onset and became seizure free following temporal lobectomy. Patients with circumscribed, potentially epileptogenic mass lesions were excluded. Fifty-four patients (81%) had histories of convulsions during early childhood or infancy, 52 of which were associated with fever. Complicated febrile seizures occurred in 33 (94%) of the 35 patients in whom detailed descriptions of the febrile seizures were available. Bacterial (5) or viral (2) central central nervous system infections were present in 7 patients with seizures and fevers. Other less common, but probably significant, risk factors included head trauma (10%) and birth trauma (3%). Only 5 patients had no apparent risk factors. The mean age at habitual seizure onset was 9 years. All patients had complex partial seizures, with half having only complex partial seizures. The other half also had secondarily generalized tonic-clonic seizures, but these were never the predominant seizure type. Only 3 patients had histories of convulsive status epilepticus and no patient had a history of nonconvulsive status epilepticus. All but 3 patients reported auras before some or all of their seizures, with an abdominal visceral sensation being by far the most common type of aura (61%). Of the 60 patients with identified risk factors, all but 2 had an interval between the presumed cerebral insult and the development of habitual seizures, with a mean seizure-free interval of 7.5 years.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of medial temporal lobe epilepsy: II. Interictal and ictal scalp electroencephalography, neuropsychological testing, neuroimaging, surgical results, and pathology.

Sixty-seven patients with temporal lobe epilepsy without circumscribed, potentially epileptogenic lesions, who were studied with intracranial electrodes and who became seizure free following temporal lobectomy were retrospectively evaluated with regard to preoperative scalp electroencephalographic (EEG) findings, neuropsychological test results, neuroimaging findings, results of surgery, and pathology of resected tissue. Interictal scalp EEG showed paroxysmal abnormalities during prolonged monitoring in 64 patients (96%). These were localized in the anterior temporal region in 60 (94%) of these 64 patients. Bilateral independent paroxysmal activity occurred in 42% of the patients and was preponderant over the side of seizure origin in half. Ictal EEG changes were rarely detected at the time of clinical seizure onset, but lateralized buildup of rhythmic seizure activity during the seizure occurred in 80% of patients. In 13%, the scalp EEG seizure buildup was, however, contralateral to the side of seizure origin as subsequently determined by depth EEG and curative surgery. Lateralized postictal slowing, when present, was a very reliable lateralizing finding. Neuropsychological testing provided lateralizing findings concordant with the side of seizure origin in 73% of patients. When neuropsychological testing produced discordant results or nonlateralizing findings, those patients were usually found to have right temporal seizure origin. Intracarotid amobarbital (Amytal) testing demonstrated absent or marginal memory functions on the side of seizure onset in 63% of patients, but 26 patients (37%) had bilaterally intact memory. In those patients who had magnetic resonance imaging, it was very sensitive in detecting subtle medial temporal abnormalities. These abnormalities were present in 23 of 28 magnetic resonance images, and corresponded with mesial temporal sclerosis on pathological examination in all but 2 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Parietal lobe epilepsy: diagnostic considerations and results of surgery.

Eleven patients, evaluated between 1983 and 1988, with parietal lobe seizure origin as determined by circumscribed lesion detection in all and successful surgery in 10, were retrospectively evaluated in terms of clinical seizure characteristics and electroencephalographic (EEG) findings. Seven of 11 patients reported auras prior to seizures. In 4 patients, auras were lateralized somatosensory sensations, but in 1 they were ipsilateral to the side of seizure origin, and in 2 they had only occurred many years previously when seizures began. Other auras were either nonspecific or suggested seizure origin outside of the parietal lobe. Observed seizures were of two types: asymmetrical tonic seizures with or without clonic activity and complex partial seizures with loss of contact and automatisms. Four patients had only the first type of seizure and an equal number had only the second type. Three patients had both types of seizures during different episodes. Scalp EEGs correctly localized the side and region of seizure onset in only 1 patient. Three additional patients with congruent parietal localization on scalp EEG had additional misleading EEG findings. All patients had lesions detected with neuroimaging, but in 5 this detection occurred after they had been initially evaluated. These 5 patients had intracranial EEG studies designed to localize the region of seizure origin, and correct seizure onset localization was achieved in 2. Of the other 3 patients, false localization occurred in 1, and 2 could not be localized. Four patients with known lesions and 2 of the patients in whom lesions were detected after initial intracranial evaluations were studied with subdural grid electrodes placed over the lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Occipital lobe epilepsy: clinical characteristics, seizure spread patterns, and results of surgery.

Twenty-five patients with occipital lobe seizure origin were retrospectively evaluated to determine clinical seizure characteristics and electroencephalographic manifestations. Certain symptoms and signs served to identify occipital lobe origin in 22 (88%). These included elementary visual hallucinations, ictal amaurosis, eye movement sensations, early forced blinking or eyelid flutter, and visual field deficits. Eye or head deviation, or both, was observed frequently and was contralateral to the side of seizure origin in 13, but 3 patients exhibited ipsilateral deviation in some or all their seizures. After the initial signs and symptoms, clinical seizure characteristics resembled those of seizures originating elsewhere. Seizures typical of temporal lobe origin with loss of contact and various types of automatic, semipurposeful activity occurred in 11 patients. Seizures in 3 patients exhibited asymmetrical tonic or focal clonic motor patterns characteristic of frontal lobe seizures. Eleven of the 25 patients had, on two occasions, two or more distinctly different seizure types. Scalp electroencephalographic findings were seldom helpful for occipital lobe localization and were frequently misleading. Intracranial electroencephalographic recording correctly identified occipital lobe seizure origin in most, but not all, patients who had such studies. Intracranial electroencephalic recording also proved the variability in clinical seizure characteristics was related to different seizure spread patterns, medially or laterally above and below the sylvian fissure, both ipsilateral and contralateral to the occipital lobe of seizure origin. Eighteen patients had occipital lobe lesions detected with computed tomographic or magnetic resonance imaging scans or both. Resection of the lesions in 16 patients produced excellent results in 14 (88%). Five patients had temporal lobectomies, with good results in 3, but poor results in 2. Two patients with unlocalized seizures had complete section of the corpus callosum, 1 with a good result and the other with a poor result.