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Biomedical subjects

P D Williamson

Publications and source records attributed to P D Williamson.

At least 19 recordsLinked to original sources
PubMed1992

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.

Adolescent↗
PubMed1992

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)

Adolescent↗
PubMed1991

Comparison of bitemporal and unitemporal epilepsy defined by depth electroencephalography.

Of 166 consecutive patients studied with depth electroencephalography (EEG), 87 had seizures arising from one temporal lobe and 23 had seizures arising independently from each temporal lobe. We retrospectively reviewed and compared those patients with unitemporal and those with bitemporal seizures. There was no statistically significant differences between the two groups in terms of age at onset of seizures, duration of epilepsy, localization of scalp EEG abnormalities, surgical results, or pathological findings. The bitemporal group, however, had significantly fewer patients with a history of febrile seizures (p less than 0.025). Two patients with bitemporal seizures were later found to have extratemporal lesions, and one an extrahippocampal temporal lesion, on magnetic resonance scans; one patient's extratemporal lesion was resected and all habitual seizures stopped. These findings suggest that a single pathophysiological process accounts for unitemporal and some bitemporal epilepsy, but that independent onset of seizures from each temporal lobe detected by depth EEG may also indicate extratemporal foci.

Adolescent↗
PubMed1991

Temporal lobectomy in patients with bitemporal epilepsy defined by depth electroencephalography.

Patient selection for temporal lobectomy was reviewed for 23 patients with seizures that arose independently from each temporal lobe as detected by depth electroencephalography (EEG). Although neuropsychological testing, interictal EEG findings, imaging studies, and subclinical seizures were also considered, all patients offered temporal lobectomy had (1) at least 50% of the clinical seizures originating from the lobe to be resected, (2) adequate contralateral memory on testing with amobarbital, and (3) no clear evidence of an extratemporal focus. Eleven patients underwent temporal lobectomy. Pathological findings were considered positive in all nine specimens reviewed. Nine patients had no seizures, one had greater than 75% reduction in seizure frequency, and 1 had 50 to 75% reduction. Pathological features and clinical outcome were similar in the 6 patients with fewer than 80% and the 5 patients with at least 80% of seizures originating from the resected lobe. Thus, having fewer than 80% of seizures originate from one temporal lobe should not be an absolute contraindication for temporal lobectomy.

Adolescent↗
PubMed1990

Chronic focal epilepsy induced by microinjection of tetanus toxin into the cat motor cortex.

The tetanus toxin model of epilepsy, involving direct microinjection of toxin into the mammalian brain, has a number of advantages relative to other chronic models. However, chronic seizure foci have been confined primarily to the hippocampus. In the present study, 5 cats received total doses of 7.5-22.5 ng of tetanus toxin applied to the left primary motor cortex through an epidural cannula. After 2-18 days, all 5 cats exhibited similar persistent epileptiform syndromes. Three distinct types of spontaneous seizures were noted: focal motor seizures of variable complexity, focal motor seizures with secondary generalization, and epilepsia partialis continua. All cats required anticonvulsant therapy. Simple focal motor seizures, which predominated, were electrographically characterized by 3-5 Hz spike-sharp wave activity, originating in the left motor cortex, associated with contralateral shoulder and forepaw clonus and jacksonian spread. Electrographic activity quickly spread to ipsilateral neocortical structures, and in longer episodes to the cingulate gyri. Seizure foci were still active as long as 37 days after toxin injection. Light microscopic damage attributable to the toxin was absent. These experiments further generalized the tetanus toxin model and confirmed its advantages.

Animals↗
PubMed1990

Combined depth and subdural electrode investigation in uncontrolled epilepsy.

We used both depth and subdural electrodes to obtain localization of the seizure focus in 47 medically refractory epileptic patients. Seizures were localized in 33 patients. Onset was consistently localized by the depth electrodes in 23 patients, was variable or simultaneous in depth and subdural electrodes in 6 (in the same lobe), and was consistently localized to subdural electrodes in 4. All patients localized with subdural electrodes were extratemporal and 3 of the 4 had lesions on imaging studies which helped guide location of electrode placement. Eighty-seven percent of temporal lobe seizures began in hippocampus (recorded by the depth electrode), and 80% were eventually propagated to the ipsilateral temporal neocortex (recorded by the subdural electrode). In 8 patients with bilateral temporal depth and subdural recording, seizures never spread to the contralateral neocortex before the ipsilateral neocortex. Subdural electrodes were 20% less sensitive than depth electrodes in detection of seizures beginning in hippocampus but were accurate when lateralized. Variable or simultaneous unilateral neocortical versus hippocampal temporal lobe seizure onset, determined by the combined study, was significantly correlated with less favorable seizure control after anteromedial temporal lobectomy and hippocampectomy.

Adolescent↗
PubMed1989

Human cortical potentials evoked by stimulation of the median nerve. I. Cytoarchitectonic areas generating short-latency activity.

1. The anatomic generators of human median nerve somatosensory evoked potentials (SEPs) in the 40 to 250-ms latency range were investigated in 54 patients by means of cortical-surface and transcortical recordings obtained during neurosurgery. 2. Contralateral stimulation evoked three groups of SEPs recorded from the hand representation area of sensorimotor cortex: P45-N80-P180, recorded anterior to the central sulcus (CS) and maximal on the precentral gyrus; N45-P80-N180, recorded posterior to the CS and maximal on the postcentral gyrus; and P50-N90-P190, recorded near and on either side of the CS. 3. P45-N80-P180 inverted in polarity to N45-P80-N180 across the CS but was similar in polarity from the cortical surface and white matter in transcortical recordings. These spatial distributions were similar to those of the short-latency P20-N30 and N20-P30 potentials described in the preceding paper, suggesting that these long-latency potentials are generated in area 3b of somatosensory cortex. 4. P50-N90-P190 was largest over the anterior one-half of somatosensory cortex and did not show polarity inversion across the CS. This spatial distribution was similar to that of the short-latency P25-N35 potentials described in the preceding paper and, together with our and Goldring et al. 1970; Stohr and Goldring 1969 transcortical recordings, suggest that these long-latency potentials are generated in area 1 of somatosensory cortex. 5. SEPs of apparently local origin were recorded from several regions of sensorimotor cortex to stimulation of the ipsilateral median nerve. Surface and transcortical recordings suggest that the ipsilateral potentials are generated not in area 3b, but rather in other regions of sensorimotor cortex perhaps including areas 4, 1, 2, and 7. This spatial distribution suggests that the ipsilateral potentials are generated by transcallosal input from the contralateral hemisphere. 6. Recordings from the periSylvian region were characterized by P100 and N100, recorded above and below the Sylvian sulcus (SS) respectively. This distribution suggests a tangential generator located in the upper wall of the SS in the second somatosensory area (SII). In addition, N125 and P200, recorded near and on either side of the SS, suggest a radial generator in a portion of SII located in surface cortex above the SS. 7. In comparison with the short-latency SEPs described in the preceding paper, the long-latency potentials were more variable and were more affected by intraoperative conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain↗
PubMed1989

Human cortical potentials evoked by stimulation of the median nerve. II. Cytoarchitectonic areas generating long-latency activity.

1. The anatomic generators of human median nerve somatosensory evoked potentials (SEPs) in the 40 to 250-ms latency range were investigated in 54 patients by means of cortical-surface and transcortical recordings obtained during neurosurgery. 2. Contralateral stimulation evoked three groups of SEPs recorded from the hand representation area of sensorimotor cortex: P45-N80-P180, recorded anterior to the central sulcus (CS) and maximal on the precentral gyrus; N45-P80-N180, recorded posterior to the CS and maximal on the postcentral gyrus; and P50-N90-P190, recorded near and on either side of the CS. 3. P45-N80-P180 inverted in polarity to N45-P80-N180 across the CS but was similar in polarity from the cortical surface and white matter in transcortical recordings. These spatial distributions were similar to those of the short-latency P20-N30 and N20-P30 potentials described in the preceding paper, suggesting that these long-latency potentials are generated in area 3b of somatosensory cortex. 4. P50-N90-P190 was largest over the anterior one-half of somatosensory cortex and did not show polarity inversion across the CS. This spatial distribution was similar to that of the short-latency P25-N35 potentials described in the preceding paper and, together with our and Goldring et al. 1970; Stohr and Goldring 1969 transcortical recordings, suggest that these long-latency potentials are generated in area 1 of somatosensory cortex. 5. SEPs of apparently local origin were recorded from several regions of sensorimotor cortex to stimulation of the ipsilateral median nerve. Surface and transcortical recordings suggest that the ipsilateral potentials are generated not in area 3b, but rather in other regions of sensorimotor cortex perhaps including areas 4, 1, 2, and 7. This spatial distribution suggests that the ipsilateral potentials are generated by transcallosal input from the contralateral hemisphere. 6. Recordings from the periSylvian region were characterized by P100 and N100, recorded above and below the Sylvian sulcus (SS) respectively. This distribution suggests a tangential generator located in the upper wall of the SS in the second somatosensory area (SII). In addition, N125 and P200, recorded near and on either side of the SS, suggest a radial generator in a portion of SII located in surface cortex above the SS. 7. In comparison with the short-latency SEPs described in the preceding paper, the long-latency potentials were more variable and were more affected by intraoperative conditions.

Cerebral Cortex↗
PubMed1989

Task-dependent field potentials in human hippocampal formation.

Task-dependent field potentials were recorded from implanted electrodes located in the hippocampus and other medial temporal lobe (MTL) structures of epileptic patients undergoing evaluation for possible surgery. In 2-alternative categorization tasks, low-probability auditory, somatic, and visual stimuli elicited potentials with large amplitudes and sharp spatial gradients having the following characteristic spatial distribution: positive posterior to the hippocampus, negative within the hippocampus, and positive anterior to the hippocampus. The sharp spatial gradients within the MTL suggest that these potentials were locally generated, probably by hippocampal pyramidal cells. The MTL potentials were also reliably elicited by exemplars of semantic categories and by stimulus omissions and were sensitive to the sequence of preceding stimuli. However, they were not elicited by the same stimulus sequences when the patient's attention was directed elsewhere and categorization was not required. These results indicate that the MTL potentials reflect endogenous as opposed to obligatory processes. The time course and task dependence of the MTL potentials suggest that MTL structures could contribute to P300 and related event-related potentials on the scalp.

Acoustic Stimulation↗
PubMed1988

Corpus callosotomy for epilepsy. I. Seizure effects.

Twenty-two patients were analyzed 2 or more years after corpus callosum section (9 partial, 13 total). Forty-one percent had class 1 outcome (elimination of secondarily generalized and complex partial seizures), 32% had class 2 outcome (elimination of secondarily generalized seizures), and 27% had class 3 outcome (no appreciable change). Total section was twice as effective in abolishing secondarily generalized seizures as was partial section (77% versus 35%). Statistically significant associations were seen between focal CT lesions and class 1 outcome, and between IQ less than 45 and class 2 or 3 outcome.

Adolescent↗
PubMed1988

Corpus callosotomy for epilepsy. II. Neurologic and neuropsychological outcome.

Eighteen uncontrolled epileptic patients had neuropsychological evaluation before and after partial or total corpus callosotomy. In patients with early-onset seizures and signs of severe unilateral CNS dysfunction, callosotomy produced no deficits and several improvements. All patients whose language-dominant hemisphere did not control their dominant hand had impairments in some aspect of speech and language function after callosotomy. In some patients, unilateral deterioration of motor function was observed, and was associated with mild to moderate dysfunction in the contralateral hemisphere (ie, memory impairment or preexisting hemiparesis). Postoperative deficits occurred with partial, as well as total, section.

Adolescent↗
PubMed1988

Localization of human sensorimotor cortex during surgery by cortical surface recording of somatosensory evoked potentials.

The traditional means of localizing sensorimotor cortex during surgery is Penfield's procedure of mapping sensory and motor responses elicited by electrical stimulation of the cortical surface. This procedure can accurately localize sensorimotor cortex but is time-consuming and best carried out in awake, cooperative patients. An alternative localization procedure is presented that involves cortical surface recordings of somatosensory evoked potentials (SEP's), providing accurate and rapid localization in patients under either local or general anesthesia. The morphology and amplitude of median nerve SEP's recorded from the cortical surface varied systematically as a function of spatial location relative to the sensorimotor hand representation area. These results were validated in 18 patients operated on under local anesthesia in whom the sensorimotor cortex was independently localized by electrical stimulation mapping; the two procedures were in agreement in all cases. Similar SEP results were demonstrated in an additional 27 patients operated on under general anesthesia without electrical stimulation mapping. The following three spatial relationships between SEP's and the anatomy of the sensorimotor cortex permit rapid and accurate localization of the sensorimotor hand area: 1) SEP's with approximately mirror-image waveforms are recorded at electrode sites in the hand area on opposite sides of the central sulcus (P20-N30 precentrally and N20-P30 postcentrally); 2) the P25-N35 is recorded from the postcentral gyrus as well as a small region of the precentral gyrus in the immediate vicinity of the central sulcus: this waveform is largest on the postcentral gyrus about 1 cm medial to the focus of the 20- and 30-msec potentials; and 3) regardless of component identification, maximum SEP amplitudes are recorded from the hand representation area on the precentral and postcentral gyri.

Anesthesia, General↗
PubMed1986

Clinical and EEG features of complex partial seizures of extratemporal origin.

Complex partial seizures (CPSs) of extratemporal origin are frequently misdiagnosed. Common reasons for diagnostic errors are failure to recognize the epileptic cause of the attacks or to appreciate localizing clinical seizure characteristics and nonspecific or misleading scalp EEG findings. This report describes clinical characteristics of two types of extratemporal CPSs, frontal and occipital. Frontal lobe CPSs are brief, frequent attacks that begin and end suddenly. They are dominated by complex, semi-purposeful motor automatisms, and vocalization and sexual automatisms are common. Their often bizarre appearance frequently leads to a misdiagnosis of hysteria. Occipital lobe CPSs are characterized primarily by their spread pattern, which can follow various paths. They may mimic temporal lobe CPSs, sensorimotor partial seizures, or supplementary motor partial seizures. Scalp EEGs are frequently misleading. The initial clinical symptoms are the most important clue to correct diagnosis and include elemental visual symptoms, visual loss, eye pulling or movement sensations in the absence of detectable movement, rapid forced blinking or eye flutter, and contralateral eye deviation.

Adult↗
PubMed1985

Comparison of carbamazepine, phenobarbital, phenytoin, and primidone in partial and secondarily generalized tonic-clonic seizures.

We conducted a 10-center, double-blind trial to compare the efficacy and toxicity of four antiepileptic drugs in the treatment of partial and secondarily generalized tonic-clonic seizures in 622 adults. Patients were randomly assigned to treatment with carbamazepine, phenobarbital, phenytoin, or primidone and were followed for two years or until the drug failed to control seizures or caused unacceptable side effects. Overall treatment success was highest with carbamazepine or phenytoin, intermediate with phenobarbital, and lowest with primidone (P less than 0.002). Differences in failure rates of the drugs were explained primarily by the fact that primidone caused more intolerable acute toxic effects, such as nausea, vomiting, dizziness, and sedation. Decreased libido and impotence were more common in patients given primidone. Phenytoin caused more dysmorphic effects and hypersensitivity. Control of tonic-clonic seizures did not differ significantly with the various drugs. Carbamazepine provided complete control of partial seizures more often than primidone or phenobarbital (P less than 0.03). Overall, carbamazepine and phenytoin are recommended drugs of first choice for single-drug therapy of adults with partial or generalized tonic-clonic seizures or with both.

Adolescent↗