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M D Nelson

Publications and source records attributed to M D Nelson.

At least 19 recordsLinked to original sources
PubMed1997

Spatial scale interactions and visual-tracking performance.

It has previously been observed that low spatial frequencies (< or = 1.0 cycles deg-1) tend to dominate high spatial frequencies (> or = 5.0 cycles deg-1) in several types of visual-information-processing tasks. This earlier work employed reaction times as the primary performance measure and the present experiments address the possibility of low-frequency dominance by evaluating visually guided performance of a completely different response system: the control of slow-pursuit eye movements. Slow-pursuit gains (eye velocity/stimulus velocity) were obtained while observers attempted to track the motion of a sine-wave grating. The drifting gratings were presented on three types of background: a uniform background, a background consisting of a stationary grating, or a flickering background. Low-frequency dominance was evident over a wide range of velocities, in that a stationary high-frequency component produced little disruption in the pursuit of a drifting low spatial frequency, but a stationary low frequency interfered substantially with the tracking of a moving high spatial frequency. Pursuit was unaffected by temporal modulation of the background, suggesting that these effects are due to the spatial characteristics of the stationary grating. Similar asymmetries were observed with respect to the stability of fixation: active fixation was less stable in the presence of a drifting low frequency than in the presence of a drifting high frequency.

Humans↗
PubMed1997

Factors affecting the recordability of auditory evoked response component Pb (P1).

The auditory middle latency response (AMLR) is characterized by two positive peaks (Pa, Pb) and two negative peaks (Na, Nb). The unpredictable nature of the second positive peak, Pb or P1, has made its diagnostic use problematic. Our purpose was to determine an appropriate combination of stimulating and recording variables that evoked a repeatable Pb in adults and children. Three experiments were designed to evaluate systematically the amplitude and latency of the Pb as a function of duration, stimulus type (500- and 4000-Hz tone bursts and clicks), repetition rate (0.5, 0.7, 1.1, 2.1, and 5.1/sec), and electrode array. Results showed that a longer duration (60 msec), low-frequency (500-Hz) tone burst consistently evoked the Pb in all subjects. Results also showed that a longer interstimulus interval (1.1/sec) is more likely to evoke the Pb component. Additionally, results showed that Pb is generally largest when recorded from a noninverting electrode at Fz with a noncephalic reference. Finally, results showed that Pb latency is significantly longer and amplitude larger in children than in adults.

Adolescent↗
PubMed1996

Usefulness of [18F]fluorodeoxyglucose positron emission tomography in pediatric epilepsy surgery.

We sought to analyze our experience with pediatric epilepsy surgery patients to determine the place of [18F]fluorodeoxyglucose (FDG) positron emission tomography (FDG-PET) in the preoperative evaluation of such children relative to chronic invasive intracranial monitoring. Fifty-six children who received an interictal FDG-PET as part of a phase 1 epilepsy surgery evaluation were compared with 44 children who did not have this study in a retrospective analysis of 100 patients accrued over a 4-year period. There was no significant difference between the two groups of children in terms of age or follow-up or was there a significant difference between the FDG-PET group and the no-FDG-PET group in regard to the numbers of children who had surgery, the type of procedure done, whether chronic invasive intracranial monitoring was performed, or outcome. The hypometabolic area demonstrated on interictal FDG-PET was concordant with that of the epileptogenic zone as mapped out with ictal recordings from subdural electrodes in 2 of 13 patients in whom a complete data set was available for comparison. In the other 11 children there was either poor agreement between interictal FDG-PET and ictal electrocorticographic data or the interictal FDG-PET was normal in the face of an epileptogenic focus which was successfully mapped by invasive electrophysiologic techniques and excised. We conclude that one cannot exclude a child with intractable partial seizures from surgical consideration because the interictal FDG-PET is normal; nor is there sufficient correlation between the interictal hypometabolic area on FDG-PET and the epileptogenic zone in terms of anatomic location and size to justify forgoing chronic invasive intracranial monitoring in children with intractable partial seizures being evaluated for epilepsy surgery unless there is absolute concordance between all neuroimaging, clinical, and video-electroencephalographic data.

Adolescent↗
PubMed1996

Surveillance imaging in children with primitive neuroectodermal tumors.

Controversy surrounds the benefits of routine surveillance magnetic resonance or computed tomographic imaging for monitoring children after resection of primitive neuroectodermal tumors. A recent study suggested that serial imaging studies detect only a small minority of tumor recurrences in patients with symptoms. The authors concluded that even in patients with recurrence documented by imaging, no patient with a recurrence survived long (average, 5 mo) and that surveillance scanning is of little clinical value in children with primitive neuroectodermal tumors. We reviewed our experience with 25 patients (28% of our total series) who presented to the Children's Hospital Los Angeles, Los Angeles, CA, from 1985 to 1993 with recurrent tumors after surgery and adjuvant therapy. Recurrent tumors were detected on routine imaging in 19 asymptomatic patients (76%) and in 6 symptomatic patients (24%). Recurrences were documented 15 months (mean) after the initial diagnosis in asymptomatic children and 5 months (mean) after the initial diagnosis in children with symptoms of recurrent tumor (P < or = 0.01). Asymptomatic patients with recurrence documented on serial imaging had prolonged survival when compared with those who were symptomatic (P < or = 0.05). The surviving patients with recurrence remained alive for more than 24 months after documentation of recurrence. Early detection of local tumor recurrence by surveillance scanning may provide a critical therapeutic window for successful treatment with aggressive or novel therapies.

Adolescent↗
PubMed1996

Ocular tolerability of timolol in Gelrite in young glaucoma patients.

BACKGROUND: Although initial patient response to timolol maleate in Gelrite (Timoptic XE) has been generally favorable in clinical settings, anecdotal reports of blurred vision warrant further investigation comparing the tolerability of this new formulation with that of timolol maleate in conventional solution. METHODS: A prospective, double-masked, randomized, cross-over study was performed using 28 normal volunteers who had no evidence of ocular disease, including glaucoma. Mean subject age was 32.5 years. Subjects were randomized to receive one drop in each eye of either timolol maleate in solution (TS) 0.5 percent or timolol maleate in Gelrite (TXE) 0.5 percent. Subjects rated each medication, using a visual analog scale, at the following time intervals: prior to drug instillation, immediately following instillation, 1 min, and at 15 min, 30 min, 1 hour, 2 hours, and 4 hours. RESULTS: Wilcoxon Matched Paris Test showed statistically significant differences at 1 minute for tearing (p = 0.003), blurred vision (p = 0.001) and drug acceptance (p = 0.028) in favor of TS. At 15 minutes and thereafter, however, none of the differences between groups was significant. Visual acuities were unaffected by either TS or TXE. CONCLUSIONS: These data suggest that TXE may impair visual function more than TS, but these effects are briefly and transitory. TXE appears to be a clinically acceptable drug delivery vehicle for use during the young glaucoma patient's waking hours.

Adrenergic beta-Antagonists↗
PubMed1995

Cognitive functioning, neurologic status and brain imaging in classical galactosemia.

A historical group of 45 children (4-18 years) and adults (18-39 years) with classical galactosemia had deficits of cognitive function that were variable and not related to the age at diagnosis or to severity of illness at presentation. There was a trend for patients to score highest on visual processing tasks. The standardized tests of speech and memory skills fell within the same range as the Broad Cognitive Ability score, indicating that the speech and language deficits may be part of a more global set of cognitive impairments. Scores on the Beery Visual Motor Integration and Block Design Tests fell in approximately the same range as other cognitive abilities. In addition, there was a high incidence of abnormality detected on MRI and 12 patients had neurologic symptoms that included ataxia, tremor and dysmetria. These abnormalities did not correlate with the age at diagnosis, severity of illness at presentation or scores on cognitive testing. The pathophysiology of neurologic and neuropsychologic impairments remains unknown. Since these appear to be unrelated to the duration of galactose exposure, other factors impacting on outcome need to be understood so that strategies can be developed to improve what appears to be a global impairment of cognitive function.

Adolescent↗
PubMed1995

Abnormal somatosensory evoked potentials in patients with classic galactosemia: correlation with neurologic outcome.

In classic galactosemia, long-term neurologic sequelae can include low cognitive functioning and a curious neurologic syndrome with tremors, dysmetria, and ataxia. An abnormal white-matter signal on cerebral magnetic resonance imaging (MRI) is present in almost all patients; some have mild cerebral or cerebellar atrophy and focal white-matter lesions. The present study was undertaken to assess the integrity of myelinated pathways by recording somatosensory evoked potentials. Results were correlated with age at diagnosis, severity of illness, age at evoked potentials, neurologic examination, MRI studies and cognitive outcome as measured by the Woodcock-Johnson Revised Standard Cognitive Battery. Evoked potentials were abnormal in 17 (28%) of 60 patients who had median nerve, and 26 (77%) of 34 patients who had posterior tibial nerve studies. Abnormalities of the central rather than the peripheral nervous system were most common. Evoked potentials correlated with severity of presenting symptoms (P = .011), age at evoked potential testing (P = .029), and presence of focal white-matter lesions on MRI (P = .049). Results of neurophysiologic testing showed no correlation with the Woodcock-Johnson Battery. Patients with classic galactosemia may have abnormal conduction along myelinated pathways that is associated with other central deficits. Myelin, which contains galactose, may be adversely affected in this inborn error of metabolism.

Adolescent↗
PubMed1995

Headache and stroke.

Explore the source record for details and available documents.

Cerebrovascular Disorders↗
PubMed1994

Subacute sclerosing panencephalitis in an infant: diagnostic role of viral genome analysis.

Subacute sclerosing panencephalitis (SSPE) is related to "defective" measles virus or vaccination, though an association with parainfluenza viruses has been reported. SSPE is characterized by a slow, erratic course and elevated cerebrospinal fluid measles titers. An immunocompetent, vaccinated infant, with onset of symptoms in parainfluenza virus season and a catastrophic course is described. Cerebrospinal fluid titers were negative, but postmortem brain had typical SSPE lesions. Patient brain-derived RNA, subjected to reverse transcription followed by polymerase chain reaction yielded polymerase chain reaction products with measles virus but not parainfluenza virus genes. The sequenced fragment revealed multiple mutations, typical for SSPE. SSPE can thus present in infants, with short latency and no cerebrospinal fluid antibodies. Viral genomic analysis may be diagnostic, permitting early therapy.

Antigens, Viral↗
PubMed1994

Real-time ultrasonography of arterial IVH in preterm infants.

The vascular origin of intraventricular hemorrhage in premature infants is controversial and has been variously attributed to arteries, veins, arterioles, capillaries, or sinusoids that may be found in the vicinity of the ganglionic eminence. The clinical histories and serial ultrasound images are reported from 2 patients with intraventricular hemorrhage of arterial (high pressure) origin that were captured on real-time ultrasonography as they occurred.

Adult↗
PubMed1994

Necrosis in pontine gliomas: radiation induced or natural history?

PURPOSE: To determine whether the central necrotic lesions that develop in a large number of patients with pontine gliomas are secondary to radiation therapy, specifically high-dose (7,200-7,800 cGy) hyperfractionation radiation therapy, or are part of the biologic progression of this tumor. MATERIALS AND METHODS: The authors analyzed neuroimaging studies of 31 consecutive patients with pontine-centered gliomas and assessed the time of onset of necrosis, the type and dose of radiation therapy administered, and the length of survival. RESULTS: Necrosis was present at diagnosis in eight of the 31 patients (26%). Time to appearance and total prevalence of central necrosis did not differ in the standard versus hyperfractionated therapy groups. The time between diagnosis and the appearance of necrosis correlated with length of survival (P = .005, Kendall correlation). CONCLUSION: In a substantial number of patients, central necrosis in pontine gliomas is not caused by radiation therapy but is an indication of an advanced tumor stage. Children with central necrosis at diagnosis have a significantly shorter median survival than do those without, regardless of the type of therapy administered.

Brain Neoplasms↗
PubMed1994

Sinusitis in status asthmaticus.

The relationship between sinusitis and status asthmaticus (SA) remains obscure. The purposes of this study were to determine the prevalence of abnormal sinus radiographs (SXRs) and investigate possible risk factors among unselected children admitted with SA. Eighty-eight patients over 2 years of age (range 2 to 16 years) consecutively admitted with SA were studied. The principal investigator, blinded to SXR findings, interviewed and examined the patients with respect to 10 physical parameters and 14 historical parameters. Two staff radiologists, blinded to the clinical findings, interpreted the SXRs. Relationship of historical and physical findings with positive SXRs was determined by statistical analysis. Twenty-seven percent of patients were found to have abnormal SXRs, manifesting two thirds or greater opacification of the sinuses. The mean age, sex, and race of patients with abnormal SXRs was not significantly different from those with normal films. A history of two or more admissions per year for SA, and, in children under 5 years of age, a history of chronic otitis media, and the physical finding of otitis media were significantly more frequent among patients with abnormal SXRs. Although not found to be statistically significant, a history of sinusitis and cough occurred more frequently in association with abnormal SXRs.

Adolescent↗
PubMed1994

Isolated lumbosacral neurenteric cyst with partial sacral agenesis: case report.

A case of an isolated intraspinal lumbosacral neurenteric cyst in a 5-year-old girl with partial sacral agenesis is reported. The cyst wall contained transitional epithelium and smooth muscle characteristic of the urinary bladder, suggesting a possible cloacal origin of the cyst. No prior cases of concomitant neurenteric cysts with partial or complete sacral agenesis have been reported, and the occurrence of an isolated intradural extramedullary sacral neurenteric cyst is rare. The possible pathogenesis of this lesion is described.

Child, Preschool↗
PubMed1993

Orofacial abscesses of odontogenic origin in the pediatric patient. Report of two cases.

Odontogenic infections rarely spread beyond the periapical space. Occasionally spread of infection into contiguous anatomic areas occurs through bone, fascial or muscular barriers. Two cases of orofacial abscess of odontogenic origin in the pediatric patient are presented, one imaged with CT and the other with MRI. Both abscesses involved the deep and superficial tissues of the face. Additionally, one of the abscesses extended into the orbit and the other involved the preseptal soft tissue. The pathogenesis, mechanism of spread and management of the disease are discussed.

Abscess↗
PubMed1993

Prenatal WIC participation can reduce low birth weight and newborn medical costs: a cost-benefit analysis of WIC participation in North Carolina.

A number of previous studies have found that prenatal participation in the Special Supplemental Food Program for Women, Infants, and Children (WIC) improves birth outcomes, but only a few studies have provided cost-benefit analyses. The present study linked Medicaid and WIC data files to birth certificates for live births in North Carolina in 1988. Women who received Medicaid benefits and prenatal WIC services had substantially lower rates of low and very low birth weight than did women who received Medicaid but not prenatal WIC. Among white women, the rate of low birth weight was 22% lower for WIC participants and the rate of very low birth weight was 44% lower; among black women, these rates were 31% and 57% lower, respectively, for the WIC participants. Multivariate logistic regression analysis confirmed that prenatal participation in a WIC program reduced the rate of low birth weight. It was estimated that for each $1.00 spent on WIC services, Medicaid savings in costs for newborn medical care were $2.91. A higher level of WIC participation was associated with better birth outcomes and lower costs. These results indicate that prenatal WIC participation can effectively reduce low birth weight and newborn medical care costs among infants born to women in poverty.

Black or African American↗