Abstract
Electroencephalography (EEG) records electrical activity of the brain and is displayed as a graph representing the difference in voltage between two different cerebral locations plotted over time.6 Our objective is to familiarize veterinarians with uses of EEG in aquatic veterinary medicine and provide a basic technique in pinnipeds for clinical use and interpretation. This method was developed at The Marine Mammal Center (TMMC) in Sausalito, CA in collaboration with the Veterinary Medical Teaching Hospital at the University of California, Davis to investigate domoic acid (DA) toxicosis in California sea lions (Zalophus californianus). DA is an excitatory neurotoxin produced by a number of marine algae, including the diatom genus Pseudonitzschia.1,4,5 California sea lions are affected by ingestion of intoxicated prey and present to TMMC with seizures and various degrees of neurological abnormalities. Some patients recover after anti-convulsive treatment and supportive care, while others have persistent behavioral abnormalities and are found to have gross hippocampal atrophy upon necropsy.3,4 Multiple methods of assessing prognosis in these patients are being investigated including magnetic resonance imaging (MRI), EEG, and cognitive assessment. At TMMC, EEG was performed on California sea lions using a method modified from human and canine techniques. Sea lions were sedated to allow placement of subdermal needle electrodes.2 An anterior posterior bipolar recording, similar to that used in human electroencephalography, was used in display of the cerebral activity. In the EEG of DA patients, epileptiform discharges, consisting of spikes, sharp waves, and spike-and-waves are often present even when clinical seizures are not apparent. These events are not observed in the EEG of patients admitted for other causes of morbidity, including malnourishment and trauma. Satellite-linked telemetry studies have indicated that DA intoxicated patients may have a poor prognosis for release.7 Further work to find a consistent prognostic indicator in these animals is warranted. From August 2004 to January 2011, 120 EEG's have been collected from stranded California sea lions. Analysis is pending to describe the EEG findings and correlate these findings with other clinical outcomes. The clinical assessment of an EEG requires recognition of normal activity in various levels of consciousness, recognition of artifacts, and an understanding of the effects of sedative drugs. An introduction to the technique and interpretation of EEG enables veterinarians to understand when EEG may be warranted. This information can be a powerful tool for veterinarians in the detection and monitoring of numerous neurological conditions.
References
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