Retrospective epidemiological study of canine epilepsy in Japan using the International Veterinary Epilepsy Task Force classification 2015 (2003–2013): etiological distribution, risk factors, survival time, and lifespan

Hamamoto et al. BMC Veterinary Research (2016) 12:248 DOI 10.1186/s12917-016-0877-3 RESEARCH ARTICLE Open Access Retrospective epidemiological study of canine epilepsy in Japan using the International Veterinary Epilepsy Task Force classification 2015 (2003–2013): etiological distribution, risk factors, survival time, and lifespan Yuji Hamamoto, Daisuke Hasegawa* , Shunta Mizoguchi, Yoshihiko Yu, Masae Wada, Takayuki Kuwabara, Aki Fujiwara-Igarashi and Michio Fujita Abstract Background: Epilepsy is the most common neurological disease in veterinary practice. However, contrary to human medicine, epilepsy classification in veterinary medicine had not been clearly defined until recently. A number of reports on canine epilepsy have been published, reflecting in part updated proposals from the human epilepsy organization, the International League Against Epilepsy. In 2015, the International Veterinary Epilepsy Task Force (IVETF) published a consensus report on the classification and definition of canine epilepsy. The purpose of this retrospective study was to investigate the etiological distribution, survival time of dogs with idiopathic epilepsy (IdE) and structural epilepsy (StE), and risk factors for survival time, according to the recently published IVETF classification. We investigated canine cases with epilepsy that were referred to our teaching hospital in Japan during the past 10 years, and which encompassed a different breed population from Western countries. Results: A total of 358 dogs with epilepsy satisfied our etiological study criteria. Of these, 172 dogs (48 %) were classified as IdE and 76 dogs (21 %) as StE. Of these dogs, 100 dogs (consisting of 65 with IdE and 35 with StE) were included in our survival study. Median survival time from the initial epileptic seizure in dogs with IdE and StE was 10.4 and 4.5 years, respectively. Median lifespan of dogs with IdE and StE was 13.5 and 10.9 years, respectively. Multivariable analysis demonstrated that risk factors for survival time in IdE were high seizure frequency (≥0.3 seizures/month) and focal epileptic seizures. Conclusions: Focal epileptic seizures were identified as a risk factor for survival time in IdE. Clinicians should carefully differentiate seizure type as it is difficult to identify focal epileptic seizures. With good seizure control, dogs with IdE can survive for nearly the same lifespan as the general dog population. Our results using the IVETF classification are similar to previous studies, although some features were noted in our Japanese canine population (which was composed of mainly small-breed dogs), including a longer lifespan in dogs with epilepsy and a larger percentage of meningoencephalomyelitis of unknown origin in dogs with StE. Keywords: Dogs, Epilepsy, Idiopathic epilepsy, Lifespan, Risk factor, Structural epilepsy, Survival time * Correspondence: Department of Clinical Veterinary Medicine, Nippon Veterinary and Life Science University, 1-7-1 Kyonan-cho, Musashino-shi 180-8602, Tokyo, Japan © The Author(s). 2016 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Hamamoto et al. BMC Veterinary Research (2016) 12:248 Background Epilepsy is a common chronic and functional brain disorder in dogs and humans that is characterized by recurrent epileptic seizures. In the veterinary field, classification and terminology of epilepsy in part reflects current proposals from the human epilepsy organization, the International League Against Epilepsy [1–4]. However, a consensus on classification and terminology in veterinary medicine had not until recently been agreed; diagnostic procedures of epilepsy are slightly different between humans and animals, therefore routine examinations in human medicine (e.g., electroencephalogram (EEG) or functional imaging) have limitations in veterinary medicine. In order to address this problem, the International Veterinary Epilepsy Task Force (IVETF) was recently organized from specialists of veterinary neurology and other neuroscientists. Accordingly, new consensus reports on canine epilepsy were published in 2015 [5–11]. According to the IVETF consensus, “epilepsy is defined as a brain disease characterized by an enduring predisposition to generate epileptic seizures” [5]. Consequently, IVETF etiologically classified canine epilepsy into idiopathic epilepsy (IdE), structural epilepsy (StE), and unknown cause [5]. Additionally, IdE is further divided into genetic epilepsy, suspected genetic epilepsy, and epilepsy of unknown cause. Classification of dogs into genetic or suspected genetic epilepsy requires genetic and/or family analysis. The IVETF criteria for IdE diagnosis is described by a three-tier system [6]. The tier I confidence level describes a history of two or more unprovoked epileptic seizures occurring at least 24 h apart, with an age at epileptic seizure onset of between 6 months and 6 years, an unremarkable interictal physical and neurological examination, and no significant abnormalities on minimum data base (MDB) blood tests and urinalysis. The tier II confidence level describes unremarkable fasting and postprandial bile acids, brain magnetic resonance imaging (MRI), and cerebrospinal fluid (CSF) analysis. The tier III confidence level describes characteristic EEG abnormalities for seizure disorders. In addition, the IVETF consensus recommends performing MRI and CSF analysis in dogs with the following conditions: age of initial epileptic seizure onset <6 months or >6 years, neurological deficits, cluster seizures (CS) or status epilepticus (SE) at initial epileptic seizure onset, and cases previously diagnosed as presumptive IdE but showing single antiepileptic drug (AED) resistance. Because the IVETF classification has only recently been defined, there have not yet been etiological or survival studies of canine epilepsy based on this classification system. Previous studies of lifespan in dogs with epilepsy have been reported using different (conventional) classifications. A recent study reported median Page 2 of 14 lifespan to be 9.2, 5.8, and 7.6 years for dogs with IdE, StE, and epilepsy from all causes, respectively [12], with premature death due to epilepsy-related causes. Moreover, some studies have focused on CS [13, 14] and/or SE [15], and reported that dogs with frequent CS may be associated with euthanasia [13], while dogs with SE may have a short survival time [15]. Here, we retrospectively inves (...truncated)