Parelaphostrongylus tenuis Cerebrospinal Nematodiasis in a Horse with Cervical Scoliosis and Meningomyelitis.

There are reports of horses with acute onset acquired cervical scoliosis and cutaneous analgesia. The underlying dorsal gray column myelitis that produces these neurologic signs has been only presumptively attributed to migration of Parelaphostrongylus tenuis within the spinal cord. Despite previous confirmation brain by polymerase chain reaction testing, of P. tenuis within the brain of horses by polymerase chain reaction testing, genetic testing has failed to definitively identify the presence of this parasite in cases of equine myelitis. This case report provides molecular confirmation via polymerase chain reaction of P. tenuis within the cervical spinal cord of a horse with scoliosis and cutaneous analgesia.

Presumptive Iatrogenic Microcystin-Associated Liver Failure and Encephalopathy in a Holsteiner Gelding.

An 8-year-old Holsteiner gelding was presented for evaluation of anorexia, obtundation, icterus, and mild colic signs of 48 hours duration. History, physical examination, and initial diagnostics were suggestive of hepatic disease and encephalopathy. Microcystin toxicosis was suspected based on historical administration of a cyanobacteria supplement, associated serum biochemistry abnormalities, and characteristic histopathological changes. Microcystin contamination was confirmed in both supplement containers fed to the horse. Fulminant hepatic failure and encephalopathy progressed resulting in euthanasia. Necropsy findings were consistent with microcystin induced liver failure.

Echo suppression in the human cortex is affected by the spatial and temporal proximity of the primary sound and echo.

Echo suppression in the human auditory cortex was studied with auditory middle latency evoked potentials (AMEP) using virtual reality acoustic stimuli, including distance and elevation cues, presented by earphones. The purpose of the study was to assess the effect of proximity of the source sound and echo on the degree of echo suppression. Sixteen subjects were presented with source-echo pairs in which the preceding source sound was always at the vertex, and the echo varied among ten positions on the coronal plane. Positions varied in elevation, distance and time lag between source and echo. The psychoacoustic location judgment of the fused source-echo pair was closer to the source sound (more echo suppression) the nearer the echo drew to the source in its elevation and time. The equivalent dipole magnitudes of the cortical components of AMEP were significantly reduced (more suppression) with shorter echo lags and when echo elevation was similar to that of the source sound. The distances used in this study did not significantly affect echo suppression. These results indicate that echo suppression in the auditory cortex is more pronounced the closer are the primary sound and echo in locational attributes and timing. As source sound and echo draw apart, echo suppression in the cortex decreases and the perceived localization of the fused source-echo is more biased toward the echo.

Short latency visual evoked potentials in occupational exposure to organic solvents.

OBJECTIVES: Short latency visual evoked potentials (SVEP), in response to high-intensity flashes from light emitting diodes (LED), were used to detect subclinical effects along the visual pathway in four groups of subjects with different levels of exposure to gasoline, all within legally acceptable limits. METHODS: Potentials and exposure levels were obtained from 31 subjects with different occupational exposure levels to gasoline fumes, as well as from 17 non-exposed control subjects. SVEP were recorded from four electrode sites (infra-orbital, Cz, Pz, Oz), in response to flashes presented to each eye in turn from goggle-mounted LEDs. SVEP components were defined after digital filtering, which eliminated the high-frequency oscillatory potentials and accentuated five major components: a periocular P30, attributed to the retina; a fronto-central N50, attributed to the optic nerve; centro-parietal P65 and N85, attributed to the optic tracts and radiation; and an occipital, cortical P105. RESULTS: The latencies of successive SVEP components of the exposed subjects showed a significant latency prolongation compared to controls, beginning with activity attributed to the optic nerve and increasing cumulatively with the later components. Retinal components were not affected by the exposure to organic solvents. Among the exposed groups, differences in latency prolongation corresponded to occupational exposure. CONCLUSION: The low-frequency components of SVEP were reliably measured and proved to be sensitive to subclinical effects of organic solvents on conduction along the visual pathway. These components are likely to be sensitive to other subcortical visual pathway lesions, but their clinical promise needs further verification.

Visual evoked potentials N75 and P100 latencies correlate with urinary delta-aminolevulinic acid, suggesting gamma-aminobutyric acid involvement in their generation.

Pattern reversal visual evoked potentials were recorded from 31 subjects who were occupationally exposed to lead and 54 non-exposed controls. No significant effects of lead were observed in the general subject population. However, when only non-smokers (17 lead-exposed and 27 controls) were evaluated, significant effects were found. The P100, but not the N75, latency was significantly prolonged in the lead-exposed group, and this correlated with both blood lead level and age. Nevertheless, both the N75 and P100 latencies correlated with the concentration of delta-aminolevulinic acid (delta-ALA) in urine and age. This, at least in part, could be due to elevated delta-ALA levels competing at gamma-aminobutyric acid (GABA) receptor neurons. This is consistent with the fact that GABA receptor neurons are involved along the entire length of the visual pathway. The results indicate that lead affects neural function even at permitted levels of exposure, and that this level should be reduced.

The effect of lead exposure on target detection and memory scanning differs.

Visual event-related potentials were measured in lead-exposed and control subjects, while they were performing a target detection as well as a memory scanning task. Blood lead and urinary delta-aminolevulinic acid (delta-ALA) were determined in samples taken on the same day. Lead exposure did not affect the memory scanning P300 latency, but it did delay the target detection P300 latency in a dose-dependent fashion. The P300 amplitude of lead-exposed subjects was significantly reduced for both tasks, but not in a dose-dependent fashion. The target detection, but not the memory scanning, P300 latency correlated with urinary delta-ALA. No correlation of P300 with age was found, even though the subjects ranged from 20 to 60 years of age. The difference in the effect of lead exposure on the target detection and memory scanning P300 adds to the evidence that the P300 for the two tasks arises from different generators. The absence of a correlation of the measured P300 latency for each task with age in the present study raises the possibility that this extensively reported observation might, in part, be due to inappropriately matched younger and older subjects. This study indicates that evaluation of subjects exposed to toxic substances can increase our basic understanding of evoked potentials, as well as providing evidence of their toxic manifestations.

Machine scoring of somatosensory evoked potentials.

A machine-scoring algorithm was developed for automatic identification and measurement of the positive and negative peaks of short-latency somatosensory evoked potentials (SEPs). The algorithm enables objective and consistent identification and naming of specific components with minimal operator involvement, avoiding inaccuracies and variability resulting from differences in the criteria used by different operators, or by the same operator at different times. The algorithm is based on finite impulse response filtering of wave forms from 4 conventional recording channels at a bandpass of 90-240 Hz. The bandpass was based on the major lobe in power spectra of multiple records and was verified as effective by application to numerous wave forms. Peak identification is based on identifying the peak at its optimal channel and verifying its consistency with corresponding peaks in the other channels. The machine-scoring algorithm was validated on SEPs from 120 subjects. The machine-scored peak latencies obtained with this procedure were significantly correlated with their manually measured counterparts.

Computational waveform analysis and classification of auditory brainstem evoked potentials.

The widely used quantitative descriptors of amplitude and latency of evoked potentials, for peaks and troughs along the waveform, relate to only a limited number of points along the waveform, ignoring the interposed data. Moreover, these descriptors are typically determined manually, rendering them susceptible to user bias. We propose and demonstrate a machine-scoring algorithm for the identification and measurement of Auditory Brainstem Evoked Potentials (ABEP) peaks I, III and V. We further introduce an algorithm for the quantitative analysis of ABEP by waveform, and for clustering records according to waveform characteristics. The results of computerized peak identification and measurement, without user intervention, were correlated with manual measurements of the same peaks in a large number of waveforms. The waveform analysis and classification procedure differentiated waveforms to monaural left, monaural right and binaural stimulation, as well as according to the recording montage. These results underscore the advantages of using information in the waveform of ABEP, which has so far been overlooked. The automated algorithms for evaluation of ABEP by waveform hold the promise of a more comprehensive and consistent evaluation, and hence improved sensitivity.