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Biomedical subjects

P Jayakar

Publications and source records attributed to P Jayakar.

At least 19 recordsLinked to original sources
PubMed1995

Electroclinical significance of rolandic spikes and dipoles in neurodevelopmentally normal children.

"Centrotemporal" (rolandic) spikes are elemental to the diagnosis of benign rolandic epilepsy (BRE) and may reveal a characteristic dipole distribution. Yet, not all children with rolandic spikes present with clinical seizures. Using additional scalp coverage according to the 10-10 electrode system, we attempted to correlate 2 specific spike features: (a) dipole fields, and (b) exact location of maximum negativity, with the presence or absence of clinical seizures in 42 neurodevelopmentally normal children with rolandic (central) spikes. Thirty-three (79%) presented with seizures. Seventeen of 21 children revealing dipoles (81%) and 16 of 21 patients without dipoles (74%) had seizures. Children with high central (C3/C4) foci were just as likely to present with seizures (10 of 15, 67%) as were those with low central (C5/C6) foci (23 of 27, 85%) (P > 0.10). The majority of our study subjects (27 of 42, 64%) revealed maximum negativity in the low central region (C5/C6), and the dipole feature was as likely to be associated with high central foci (7 of 15, 47%) as with low central foci (14 of 27, 52%). Although rolandic spikes are a reliable indicator of potential epileptogenicity, neither their exact location nor dipolar distribution help to further define the population with clinical seizures.

Brain↗
PubMed1995

Cuban embargo.

Explore the source record for details and available documents.

Commerce↗
PubMed1994

Posterior temporal epilepsy: electroclinical features.

In the course of evaluating children with posterior temporal lobe epilepsy with subdural electrodes, we observed that their seizures commonly arose from basal rather than convexity foci and that they followed a stereotyped clinical sequence. Seizures characteristically began with behavioral arrest that coincided with basal temporal seizure discharges and progressed to motor signs as the seizure activity spread to the ipsilateral cortical convexity. Behavioral automatisms were observed in approximately half the patients, but were never the first or most prominent ictal manifestation. Focal lesions were identified preoperatively in 7 patients. We performed tailored temporal lobe resections in 14 patients, 10 (71%) of whom were seizure free (N = 9) or had occasional auras (N = 1) at a mean follow-up of 2 years. These findings suggest that in childhood, posterior temporal seizures frequently arise from basal cortex and have a consistent and recognizable ictal and electrographic semiology. In medically refractory patients, tailored temporal resection is an effective therapy.

Adolescent↗
PubMed1994

Medical intractability in children evaluated for epilepsy surgery.

We assessed the value of therapeutic reevaluation and additional pharmacotherapy in medically intractable children referred for epilepsy surgery. In 21 children with antiepileptic drug treatment omissions, correcting the omission was ineffective in 19 (90%). Two children (10%), both of whom had structural lesions, achieved significant seizure control with high-dose carbamazepine monotherapy. Therapeutic reevaluation is indicated in all medically intractable children prior to epilepsy surgery.

Adolescent↗
PubMed1994

Early surgery for epilepsy: redefining candidacy.

Surgical resection for localization-related epilepsy has recently become a generally accepted treatment in children. Evidence of the poor outcome in natural history studies of temporal lobe epilepsy in childhood initiated consideration of surgical intervention. Subsequent favorable outcome following surgery was encouraging. A number of variables differentiate adults with focal seizures from children. Evolving biologic factors modify the clinical and electroencephalographic expression of seizures in childhood. The pathologic substrate is different, and there is a higher incidence of extratemporal epilepsy. Chronic seizures beginning under age 2 years rarely remit, especially when associated with a demonstrable structural lesion. Behavioral consequences of chronic seizures are significant and become a major problem by adolescence if seizures are not controlled. Early surgery results in superior functional outcome, although subtle deficits persist postoperatively. Surgical outcome is as favorable as in adults with improvements in behavioral status and socialization. Abundant data exist to more adequately assess the benefits and risks of surgery in children so that intervention is not deferred longer than it needs to be.

Adolescent↗
PubMed1994

Neurobiologic considerations in early surgery for epilepsy.

Children with well-localized medically resistant seizures are often referred for surgical therapy. In young children, at least three maturational issues play a significant role in the selection process and long-term outcome. First, the early years are a time of exceptionally rapid brain development leading to dynamic changes in the electroencephalogram and the clinical expression of seizures. Many early-onset seizure presentations are also associated with catastrophic outcomes, developmental arrest, or regression. Second, the immature limbic system may be vulnerable to stresses operating in early life, although the consequences may not become apparent for many years. Third, in comparison to the adult, the child's nervous system typically exhibits superior functional recovery after lesioning, but the process of sparing and recovery is often incomplete. An understanding of how these neurobiologic factors influence developmental outcome will ultimately lead to greater selectivity of candidates for early surgery and to improved long-term prognosis.

Animals↗
PubMed1994

Subdural monitoring in the evaluation of children for epilepsy surgery.

Noninvasive assessment of children with chronic epilepsy is often imprecise and localization of seizure foci requires intracranial electroencephalographic monitoring. Subdural electrodes provide coverage of large areas of neocortex and are ideally suited for evaluating children with intractable epilepsy and to functionally map critical cortex. This report discusses the role of subdural electroencephalography in the evaluation of childhood epilepsy.

Brain Mapping↗
PubMed1992

A safe and effective paradigm to functionally map the cortex in childhood.

Conventional cortical stimulation based on pulses of fixed duration briefer than the chronaxie rarely elicit responses in infants and young children. We developed a stimulation paradigm that relies on increments in both stimulus intensity and pulse duration. This approach ensures that stimulation parameters converge to the chronaxie by mathematically minimizing the energy required to elicit a response. In six patients, this paradigm successfully elicited clinical responses and/or afterdischarges at thresholds 5-8 mA below the standard paradigm and at up to 64% lower energy levels. Furthermore, three patients under age 5 years who did not respond to maximal fixed duration stimulation demonstrated afterdischarges and clinical responses when longer pulse durations were utilized. These findings indicate that a paradigm based on dual increments is effective for cortical mapping in children. Furthermore, by ensuring responses at lower energy levels, it may be more efficient for mapping the cortex at all ages.

Brain Mapping↗
PubMed1992

Ictal head deviation: lateralizing significance of the pattern of head movement.

To resolve the controversy surrounding the lateralizing value of ictal head deviation, we analyzed head-turning movements in relation to the actions of the two divisions of the sternocleidomastoid muscle. In 12 (75%) of 16 patients with surgically confirmed lateralized seizure foci, the face rotated upward and contraversive to the hemisphere of seizure origin, consistent with activation of the ipsilateral sternomastoid muscle. One patient showed a sustained, downward ipsiversive head tilt consistent with the action of the ipsilateral cleidomastoid muscle, and three patients had a combined ipsiversive head tilt and contraversive face rotation. No patient exhibited ipsiversive upward face rotation or contraversive head tilting, as would be expected if the contralateral sternocleidomastoid were activated. Our findings indicate that hemispheric seizure foci activate one or both divisions of the ipsilateral sternocleidomastoid muscle. Accurate lateralization of the seizure focus is possible only when ictal head deviation is assessed in the context of the different actions of the sternomastoid and cleidomastoid muscle divisions.

Adolescent↗
PubMed1991

Localization of epileptogenic foci using a simple reference-subtraction montage to document small interchannel time differences.

We present a modified EEG montage that detects small interchannel time differences and assists in localizing the epileptogenic focus. Regions with apparently synchronous epileptic discharges are displayed simultaneously in referential and subtraction derivations. The subtraction derivation is a bipolar configuration of two regions of interest that are not necessarily adjacent. The referential derivation reveals the polarity, voltage, and morphology of the two discharges, and the subtraction derivation detects asynchrony; the combined reference-subtraction derivation thus indicates the region that is activated first.

Electroencephalography↗
PubMed1991

Localization of seizure foci: pitfalls and caveats.

The pitfalls and difficulties in accurately localizing seizure foci are reviewed. Basic issues regarding modeling, volume conduction, inhomogeneities, and corticocortical propagation are discussed, and the limitations of scalp and intracranial recordings are outlined. The ambiguities in interpreting patterns and their significance are highlighted with a concluding commentary on pitfalls in defining the epileptogenic region.

Brain↗
PubMed1990

Clinical correlations of photoparoxysmal responses.

Reilly and Peters (1973) reported that photoparoxysmal responses (PPRs) that outlasted the stimulus correlated significantly with seizures as compared to self-limited PPRs. However, they defined a wide range of activity, including occipital spikes and slow wave bursts, as PPR. We examined EEGs of 3557 patients and 48 normal subjects for PPRs defined only as generalized spikes or spike-wave activity. None of the 48 normal subjects showed a PPR. PPRs were seen in 35 (1%) patients, 27 (77%) of these had a definite history of epilepsy, 3 (9%) had a questionable history, and 5 (14%) had had no seizures. PPRs were prolonged more than 100 msec beyond the stimulus in 11, and self-limited in 24. The incidence of seizures was not statistically different in these 2 groups. Furthermore, the classification of PPRs into these 2 groups could be influenced by the time at which the stimulus was stopped after the appearance of the PPR. PPRs are rare in normal subjects and non-epileptic patients and have a high correlation with seizures irrespective of their relationship to the strobe stimulus.

Adolescent↗
PubMed1989

Automated rule based graded analysis of ambulatory cassette EEGs.

We describe algorithms, developed on a PDP-11/73 microcomputer, which identify spikes/sharp waves (STs), spike-and-wave complexes (SSWs), artifacts and background activity in 4-channel ambulatory EEGs. The algorithms were trained using 40 database segments. Time domain/mimetic methods were used and semantic rules, based on morphology and multi-channel contextual information, were developed to mimic the principles used in visual interpretation. The likelihood of STs/SSWs being genuine was graded from 10 to 1. This approach avoids forced classification of each event as genuine ST/SSW or not. The algorithms were then evaluated using 60 independent segments. STs/SSWs graded greater than 7 had significantly higher probability (P less than 0.005) of being genuine than those graded less than or equal to 7. Less than 4% of STs/SSWs identified by both electroencephalographers were missed. None was distinct. All 113 artifacts resembling STs/WWs were graded less than or equal to 7. Classification of 969/1117 (86%) waves in the background matched that of one electroencephalographer. The algorithms can be extended to 8- or more-channel EEGs.

Algorithms↗