The possibilities of AEEG as a diagnostic tool for epilepsy in horses.

Abstract

Introduction: (A)EEG ((ambulatory) electroencephalography) is a method to record brain waves over a period for more than forty-eight hours. The method is used routinely for diagnostics and pre surgical procedures in human patients suffering from epilepsy(Empson 1986a; Patel et al. 2009; Rose and Hodgson 2000; Shih et al. 2009; Swartz and Goldensohn 1998). In horses still insufficiently research is done to use (A)EEG as a diagnostic tool for epileptic(Aleman et al. 2006; Lacombe et al. 2001; Williams et al. 2008). Objective: The aim of the study is test the hypothesis that AEEG can be used for longterm recordings in unsedated horses for identification of abnormalities, for instance epilepsy. Material and methods: The control group contained 8 healthy horses. The patient group contained 7 horses. Patients showed clinical signs of abnormal behaviour of unknown origin or epileptic–like insults as judged by their own vet. Electrode placement was determined based on the human system in combination with MRI examination of a head. 9 self adhesive electrodes were positioned. The ‘Porti-5’ recording system was attached underneath a metal roll-band on top of a girdle. The records were analysed making montages to compare the signals of the electrodes with each other. The filter settings were 0,5 Hz high pass and 35 Hz low pass. The records were analysed off-line at an amplitude of 50-200uV and 10 seconds time scale by visual inspection. Epileptic activity was defined as records containing a spike (a sharp wave of 70-200Hz), a period of rhythmical activity (longer period of similar waves of 1-1,5Hz) or a fast rhythmic discharge (short period of high amplitude waves of 4-7Hz) ((Aleman et al. 2006; Beleza et al. 2009; Liasis et al. 2006; Tassi et al. 2009). In one patient a post-mortem MRI was made. Results: The recording time varied from 6 until 48 hours. All the cases showed normal brain signals(Aleman et al. 2006; Empson 1986a; Williams et al. 2008). 57% of the patient group showed brain signals indicating pathology. 43% of the patient group and 12%(n=1) of the control group showed epileptic activity(Aleman et al. 2006; Beleza et al. 2009; Liasis et al. 2006; Tassi et al. 2009). One horse showed slow delta wave’s indicative of brain pathology in the left side of the brain. A post-mortem MRI showed a large left-sided abscess. Conclusions: Long-term records of good quality of horses brain waves were made with AEEG, resulting in a reasonable chance to record pathological signals indicating epileptic of pathological activity in absence of obvious abnormal behaviour. Practical significance: Intermittent abnormal behaviour can be normal by the time the veterinarian arrives. Still, horse owners will ask for a diagnosis and therapy. For insurance issues or just for their own comfort, it is important to develop a system to do identify abnormal brain activity.