Epilepsy & Behavior Epilepsy & Behavior 4 (2003) 198–201 www.elsevier.com/locate/yebeh
Letters to the Editor
Re: Clinical presentations of naturally occurring canine seizures: similarities to human seizures To the Editor: We commend Licht et al.  for presenting informative and valuable data on canine seizure symptomatology and for once again stressing the striking resemblance of the clinical expression of canine and human epileptic seizures. The diagnosis of epilepsy is essentially clinical and based on a bona ﬁde history of epileptic seizures. Consequently, recognition of the clinical manifestations of seizures represents the most important criterion for establishing a diagnosis of epilepsy . By their thorough questioning of the dog owners, the investigators have paid special attention to initial seizure signs, thereby increasing the possibility of identifying a partial seizure origin that might otherwise have remained obscure. The results of their study strongly support existing data suggesting that partial seizures with secondary generalization are the most common seizure type in dogs, as is also the case in humans [3–7]. However, in the interest of the ongoing revision of the seizure classiﬁcation system, we have some comments that we would like to share. As correctly noted by the authors, signs described as auras, in a substantial number of cases of epilepsy previously described in the veterinary literature, have not been recognized as a part of the ictus (namely the partial onset in a partial seizure with secondary generalization), or as the ictus itself (as in partial seizures alone), but have been believed to represent a preictal event. As a consequence, these epileptic seizures have erroneously been classiﬁed as primary generalized seizures (the type of seizures predominantly characterizing idiopathic epilepsy), thus leading to the misunderstanding that most canine epilepsies are idiopathic. Based upon the above reﬂections we are puzzled by the overall assumption made by the investigators that the entire study population suﬀers from idiopathic epilepsy, since this statement is strongly contradicted by their results identifying a partial seizure origin in 80% of the dogs. This ﬁgure strongly suggests that the vast majority of these dogs may more likely be suﬀering from symptomatic or cryptogenic epilepsy.
Many human patients with partial seizures present without neurological signs, with normal MRI scans, and with normal interictal EEGs and are classiﬁed as having cryptogenic epilepsy, if the family history does not point toward an idiopathic familial epilepsy. One could argue that since the dogs participating in the present study were purebred dogs and therefore might be closely related, they could theoretically be suﬀering from idiopathic partial epilepsy. In man, idiopathic (benign) partial epilepsies of childhood are well described and account for about 10–15% of epilepsy cases in this age group . Clinical features include epilepsy with partial seizures, absence of clinical or neuroimaging evidence of brain damage, characteristic interictal EEG focal sharp waves with variable location, a possible family history of idiopathic epilepsy, onset of seizures between 18 months and 13 years, and spontaneous remission of epilepsy during childhood or adolescence. In the present study, however, the investigators tried to avoid collecting dogs from the same bloodlines in order to avoid selection bias. To prevent future confusion we suggest that the term ‘‘idiopathic’’ be reserved for those cases of epilepsy predominantly presenting with primary generalized seizures, in which a symptomatic origin is neither detected nor suspected, and that the term ‘‘symptomatic’’ be used only for epilepsy caused by a known/identiﬁed disorder of the CNS (focal structural cerebral pathology) and presenting as partial seizures with or without secondary generalization. The present study addresses the question of simple and complex partial seizures. In animals, diﬃculties in recognizing the owner or other signs of confusion may be interpreted as signs of impaired consciousness. In the Danish Epilepsy Research Team we have, however, with time come to the conclusion that the question of mental cloudiness in dogs and cats represents a true problem because the patients cannot report what they are actually experiencing during a seizure. We believe that the clinical signs alone (as interpreted by the owner and/or from videotaped episodes)—without EEG registration— do not really oﬀer enough objective data to justify discrimination between simple and complex partial seizures in animals. We therefore suggest that no such distinc-
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Letters to the Editor / Epilepsy & Behavior 4 (2003) 198–201
tion be made based upon clinical signs alone. Pragmatically, a distinction between simple and complex partial seizures in dogs is of little importance as the treatment will be the same. In man, the distinction may be decisive for the possibility of getting or keeping a driverÕs license. In recent years, revision of the 1981/1989 ILAE classiﬁcation has been under active discussion. Seizure classiﬁcation based exclusively on ictal semiology, either as reported by the patient or by an observer or as analyzed directly by video monitoring, has been proposed [9,10]. In such a classiﬁcation system, EEG or other test results do not inﬂuence the classiﬁcation. A new ILAE classiﬁcation will include more criteria for classiﬁcation than descriptive terminology for ictal phenomena, e.g., classiﬁcation of seizures based upon known or presumed pathophysiological and anatomic substrates . It is of great interest for veterinary neurology to follow the development of a revised human epilepsy classiﬁcation closely. These data can be of value for future endeavors to expand the classiﬁcation of canine and feline epilepsy. Based upon anecdotal evidence, a relationship between the type of epilepsy and the age at ﬁrst seizure is believed to exist in canines. Dogs with symptomatic epilepsy (characterized by partial seizures) are believed to experience their ﬁrst seizure either in the ﬁrst year of life or later than the age of 4 as opposed to dogs experiencing canine idiopathic epilepsy (predominated by primary generalized seizures) in which the ﬁrst seizure is believed to occur prior to the age of 5. The results of a recent epidemiological cross-sectional study of Danish Labrador retrievers could not support this assumption. The Danish study showed that among dogs suﬀering from partial seizures with or without secondary generalization, 83% experienced their ﬁrst seizure before the age of 4 . There is a great need for descriptive studies on canine epilepsy. The authors of the present study should once again be congratulated for their great eﬀort in presenting an informative study that adds important information on canine seizures and thereby increases our knowledge of canine epileptology.
References  Licht BG, Licht MH, Harper KM, et al. Clinical presentations of naturally occurring canine seizures: similarities to human seizures. Epilepsy Behav 2002;3:460–70.  Commission on Epidemiology and Prognosis, International League against Epilepsy. Guidelines on epidemiology and prognosis, International League against Epilepsy. Epilepsia 1993;34:592–6.  Podell M, Fenner WR, Powers JD. Seizure classiﬁcation in dogs from a nonreferral-based population. J Am Vet Med Assoc 1995;11:1721–8.  Heynold Y, Faissler D, Steﬀen F, et al. Clinical, epidemiological and treatment results of idiopathic epilepsy in 54 Labrador retrievers: a long-term study. J Small Anim Pract 1997;38:7–14.  Berendt M, Gram L. Epilepsy and seizure classiﬁcation in 63 dogs: a reappraisal of veterinary epilepsy terminology. J Vet Intern Med 1999;13:14–20.  Berendt M, Gredal H, Pedersen LG, et al. A cross-sectional study of epilepsy in Danish Labrador retrievers: prevalence and selected risk factors. J Vet Intern Med 2002;16:262–8.  Hauser WA, Annegers JF, Kurland LT. The incidence of epilepsy and unprovoked seizures in Rochester, Minnesota, 1993–1984. Epilepsia 1993;34:453–68.  Loiseau P. Idiopathic and benign partial epilepsies of childhood. In: Wyllie E, editor. The treatment of epilepsy: principles and practice, second ed. Baltimore: Williams & Wilkins; 1996. p. 442–50.  L€ uders HO, Burgess R, Noachtar S. Expanding the international classiﬁcation of seizures to provide localization information. Neurology 1993;43:1650–5.  L€ uders H, Acharya J, Baumgartner C, et al. Semiological seizure classiﬁcation. Epilepsia 1998;39:1006–13.  Engel J. Classiﬁcation of the International League against Epilepsy: time for reappraisal. Epilepsia 1998;39:1014–7.
Mette Berendt* The Royal Danish Veterinary and Agricultural University Copenhagen Denmark Mogens Dam Brovænget 36, Virum Denmark E-mail address: [email protected]
(M. Berendt) doi:10.1016/S1525-5050(02)00686-8 * Corresponding author.
Reply To the Editor: We welcome the comments of Dr. Berendt and Dr. Dam as a critical dialogue is needed to help advance the classiﬁcation of canine seizures and epilepsies. The primary concern that they raise with regard to our article is
that we did not assume, as they do , that partial (focal) onset seizures must lead to a diagnosis of either symptomatic or cryptogenic (probably symptomatic) epilepsy. Thus, they argue that our ﬁnding that at least 80% of both breeds (Poodles and Dalmatians) experienced partial onset seizures should have led us to