Semiological and etiological classification of seizures in cats and dogs: 53 cases

Abstract

Epileptic seizures in cats and dogs are etiologically classified as idiopathic epilepsy, structural epilepsy and reactive seizures, and semiologically as atonic, tonic/clonic, or generalized tonic clonic, focal and focal seizures evolving into generalized seizures. This retrospective study aimed to evaluate the semiological patterns and etiological causes of seizures in both species, and to assess interspecies differences in a regional veterinary population. Between January 2022 and January 2025, 77 cats and 106 dogs presented with seizures to Ondokuz Mayis University Animal Hospital (Samsun/Turkiye). After exclusions due to insufficient data or financial constraints, 24 cats and 29 dogs were included based on the Tier-I diagnostic criteria proposed by the International Veterinary Epilepsy Task Force. The relationships between species, age, sex, neuter status, seizure semiology and etiology were analyzed. Generalized tonic-clonic seizures were observed in 83.3% of cats and 72.4% of dogs. Idiopathic epilepsy was diagnosed in 41.7% of cats and 55.2% of dogs. Structural epilepsy in cats was mainly associated with feline infectious peritonitis, while canine distemper virus was the predominant cause in dogs. Although seizure types were broadly similar across species, some etiological differences appeared regionally. The high rate of generalized seizures may reflect observer bias or challenges in accurately classifying semiology without electroencephalography. This study highlights the utility of tiered diagnostic approaches in veterinary epileptology and underscores the need for updated, species-specific consensus guidelines for diagnostic approach and classification especially in feline patients.

INTRODUCTION

Epileptic seizures occur as a result of excessive synchronization of neuronal activity in the brain and cause focal, motor, autonomic or behavioral changes that are usually self-limiting and episodic, or generalized manifestations that affect both hemispheres and are typically associated with impaired consciousness. Seizure types are currently classified in veterinary terminology into three groups: focal (motor, autonomic, behavioral), generalized (atonic, tonic, clonic, tonic-clonic, myoclonic) and focal seizures evolving into generalized seizures [2]. Focal seizures evolving into generalized seizures are characterized by an initial focal onset that rapidly progresses to bilateral motor activity. Their recognition is often difficult for general practitioners, as the early focal signs are typically brief and easily overlooked [2].

In dogs, epilepsy is classified etiologically according to the Internal Veterinary Epilepsy Task Force (IVETF) into three categories: reactive seizures; structural epilepsy and idiopathic epilepsy [2]. Seizures caused by metabolic or toxic extracranial problems are called reactive seizures and these seizures are reversible when the underlying cause is successfully treated [2, 6, 14]. Structural epilepsy caused by a structural forebrain disorder that can be defined as vascular, inflammatory/infectious, traumatic, abnormal/developmental, neoplastic and degenerative diseases [2, 7, 16].

Idiopathic epilepsy (IE) is defined by the IVETF both as a diagnosis of exclusion and collective term that includes multiple etiological forms. In dogs, IE encompasses case where extracranial and intracranial causes of seizures have been ruled out, as well as genetically confirmed epilepsy based on breed-specific mutations, and suspected genetic epilepsy characterized by a breed prevalence exceeding 2% without a known mutation [2, 7]. The IVETF consensus report recommends a three-tier diagnostic approach for idiopathic epilepsy in dogs. Tier-I is based on seizure history, normal interictal clinical findings and unremarkable minimum laboratory database results. Tier-II adds brain magnetic resonance imaging (MRI) and cerebrospinal fluid (CSF) analysis to exclude structural disease. Tier-III includes electroencephalography (EEG) confirmation of epileptiform activity [8].

The same etiological classification and diagnostic method used in dogs is often used in cats as well [12, 13]. However, unlike dogs, there is no established consensus guideline specific to epilepsy in cats, which can lead to terminological differences in research. Still, the IVETF classification can be used for cats in both clinical practice and research, as it helps to distinguish seizure causes based on underlying mechanisms [19].

In previous studies, it has been reported that seizures have a structural origin in 60% of cats and 50% of dogs, and idiopathic epilepsy is more frequently observed in dogs [22, 24, 27]. The prevalence of reactive seizures in cats and dogs is similarly 5–7.9% and it has been reported that they are frequently caused by toxication [3, 14]. The etiological causes of seizures vary regionally and semiological classifications vary according to different common statements.

The primary aim of this study was to evaluate species-related differences in the semiological classification of seizures in dogs and cats. A secondary objective was to determine the etiological distribution and underlying causes of seizures, based on cases presented to a single referral center, in the Black Sea region of Turkiye. The study aimed to provide comparative data by determining the regional prevalence of seizure etiologies and to contribute to the literature.

MATERIALS AND METHODS

Case selection

Among 49,698 cats and 25,073 dogs admitted to Ondokuz Mayis University Faculty of Veterinary Medicine Animal Hospital (located in the city of Samsun, in the Black Sea region of Turkiye) between January 1, 2022 and December 31, 2024, medical data of 77 cats and 106 dogs with seizure complaints were analyzed (Fig. 1). Ethical committee approval was received for this study from the Ethics Committee of Ondokuz Mayis University (Approval number/date: 2015-17/March 20, 2025).

Fig. 1.

Number of patients with analyzed medical data. *: Patients undergoing minimum IVETF Tier-I diagnostic procedures.

Analyzing medical records

Patient information, including age, gender, neutering status, and the semiological classifications of seizures and etiological classifications of epilepsy were recorded. Dogs and cats with a diagnosis of seizures based on physical and neurological examination, complete blood count, serum biochemistry, electrolyte panel, and urine analysis were included, in accordance with the Tier-I diagnostic approach recommended by the IVETF [8]. Dogs age between 6 months and 6 years presenting with at least two unprovoked seizures more than 24 hr apart, exhibiting normal inter-ictal neurological examination findings and having normal results in Tier-I laboratory diagnostics as defined by IVETF were classified as idiopathic epilepsy. Dogs younger than 6 months or older than 6 years, or those exhibiting abnormal inter-ictal neurological findings or a history of behavioral changes, underwent Tier-II diagnostics and were included accordingly.

For cats, in the absence of a standardized consensus for idiopathic epilepsy diagnosis, individuals that met at least the Tier-I diagnostic criteria proposed by the IVETF were included in the study. Cats with a serum albumin/globulin ratio of 0.5 or less and at least two compatible clinical signs (e.g., uveitis, ascites with positive Rivalta test, incoordination, or ataxia) were diagnosed with feline infectious peritonitis (FIP) according to diagnostic methods established by the AAFP/ EveryCat task force [29]. A rapid serological test for the detection of IgG and IgM antibodies against Toxoplasma gondii (Healvet^®, Shenzhen, China) was used as a diagnostic criterion in cats. CSF samples were analyzed using Polymerase Chain Reaction (PCR) or Enzyme-Linked Immunosorbent Assay (ELISA) analysis was used to diagnose the canine distemper virus (CDV). Data were excluded when diagnostic procedures could not be completed due to financial constraints.

The presence and type of seizures were determined using a video and/or IVETF’s “standardized epilepsy investigation questionnaire” and included in the study [8]. Cases without either questionnaire or video findings were excluded.

Patients were excluded if physicians did not determine the semiological classification of seizures. Patients were excluded if their medical records contained insufficient data for etiological and semiological identification. Seizures were semiologically categorized as atonic, tonic or clonic, focal, and generalized tonic-clonic. Epilepsy was classified as idiopathic and structural (infectious, inflammatory, neoplastic, vascular, traumatic), while seizures resulting from metabolic and toxic causes were defined as reactive seizures according to their etiological origin.

Statistical analysis

Statistical analyses were performed with the IBM SPSS (v26) package analysis program. Categorical data (etiological diagnosis, semiological diagnosis, sterile status, gender) were subjected to statistical analyses with a χ² test. Atonic and tonic or clonic seizures were combined and included in the analyses as a single group (focal/non-generalized seizures). Statistical analyses in the age variable between the subheadings of etiological and semiological diagnoses were performed with the Kruskal-Wallis test. Descriptive statistics in the tables were shown as mean ± standard deviation (SD) and median value. The statistical significance level was accepted as P≤0.01.

RESULTS

Between January 2022 and January 2025, a total of 106 dogs (0.42%) and 77 cats (0.15%) out of 25,073 dogs and 49,698 cats, respectively were admitted to the clinic with seizure signs. Seventy-seven dogs and 53 cats were excluded from the study. In 13 cats and 9 dogs, the owners refused the diagnostic procedures required to determine the etiology of seizures due to financial constraints. Forty cats and 68 dogs were excluded from the study due to missing data (seizure type, diagnostic procedures performed, and demographic data). The final study group included 24 cats- British Shorthair (n=3), Scottish Fold (n=1), Domestic Longhair (n=6), Domestic Mediumhair (n=7), and Domestic Shorthair (n=7) and 29 dogs- Rottweiler (n=1), Pug (n=2), German Shepherd (n=1), French Bulldog (n=1), Shih Tzu (n=2), Maltese Terrier (n=2), Yorkshire Terrier (n=5), Golden Retriever (n=1), Pomeranian (n=2), Chihuahua (n=1), Small Munsterlander (n=1), Border Collie (n=2), Poodle (n=1), and mixed-breed (n=7) (Supplementary Table 1). Video recordings are available for 19 of the 24 cats and 23 of the 29 dogs included in the study, and the IVETF’s standardized epilepsy investigation questionnaire is available for all patients included in the study.

Of the 24 cats, 18 were male (7 neutered) and 6 were female (1 neutered). Of the cats, 41.7% (n=10) were diagnosed with idiopathic epilepsy, 37.5% (n=9) with structural epilepsy and 20.8% (n=5) with reactive seizures. Of the dogs, 55.2% (n=16) were diagnosed with idiopathic epilepsy, 34.5% (n=10) with structural epilepsy and 10.3% (n=3) with reactive seizures (Table 1). Relative to the total clinical population, the proportion of idiopathic epilepsy cases was 0.06% in dogs and 0.02% in cats, respectively.

Table 1. The frequencies of semiological and etiological diagnoses and age demographic data of the dogs and cats included in the study were summarized in the table. Statistical analyses were performed between the frequencies of generalized tonic-clonic and focal seizures as semiological, idiopathic epilepsy, and reactive seizures as etiological.

	Cat	Dog	Cat age (mean ± SD) (median)	Dog age (mean ± SD) (median)	Sterilized cat	Sterilized dog
Atonic	0 (0%)	2 (3.8%)	30.50 ± 6.36 (30.50)	30.50
T/C	1 (4.2%)	3 (7.5%)	50.00 ± 33.15	65
GTC	20 (83.3%)	21 (72.4%)	28.40 ± 18.48 (30.50)	87.42 ± 56.12 (68)	7	4
Focal	3 (12.5%)	3 (10.3%)	29.33 ± 14.01 (25)	51.33 ± 54.92 (37)	1	2
IE	10 (41.7%)	16 (55.2%)	35.50 ± 19.65 (34.50)	72.81 ± 36.36 (64.50)	4	4
RS	5 (20.8%)	3 (10.3%)	23.80 ± 19.63 (31)	113.00 ± 91.65 (133)	0	1
SE	9 (37.5%)	10 (34.5%)	22.44 ± 11.22 (18)	69.70 ± 67.25 (41)	0	1
P-value			0.21	0.46

IE: idiopathic epilepsy, RS: reactive seizure, SE: structural epilepsy, T/C: tonic or clonic, GTC: generalized tonic-clonic, values in parentheses median values. Percentages (%) indicate the proportion of cats or dogs within each category.

Among the 9 cats classified as structural epilepsy, 7 were diagnosed with FIP and 2 with toxoplasmosis-associated encephalopathy. Among the 5 cats classified as having reactive seizures, 3 were due to antiparasitic intoxication, 1 due to hyperammonemia, and 1 due to hyperthyroidism. Among the 10 dogs classified with structural epilepsy, 6 had CDV, 2 had neoplastic lesions, 1 was suspected to have hydrocephalus, and 1 had a bacterial meningoencephalitis. Among the 3 dogs classified with reactive seizures, one was due to azotemia, 1 to multiple organ failure, and 1 to hepatic encephalopathy.

Seizures were classified semiologically into two main categories: generalized and focal/non-generalized (including atonic, tonic, and clonic types). Generalized tonic-clonic seizures were the most common seizure type, recorded in 83.3% (n=20) of cats and 72.4% (n=21) of dogs (Table 1). Focal seizures were recorded in 12.5% (n=3) of cats and 10.3% (n=3) of dogs. Atonic seizures were recorded in only 2 dogs. Only tonic or clonic seizures were recorded in 4.2% (n=1) of cats and 7.5% (n=3) of dogs (table 1). There was no statistically significant difference in the frequency distribution of generalized and focal/non-generalized seizures between cats and dogs (P>0.05).

DISCUSSION

Zero point one five % of cats admitted to the clinic had seizures. Of these, 0.06% were diagnosed with idiopathic epilepsy. A similar study reported seizure and idiopathic epilepsy prevalence rates of 0.16% and 0.04% in a large feline population in the United Kingdom [19]. In this study, the proportion of dogs presenting with seizures was 0.42%, and 0.06% were diagnosed with idiopathic epilepsy. In another study reported a 1-year seizure prevalence of 0.82% in dogs [9]. Differences in population size, case selection, and diagnostic criteria may explain this variation [9, 16, 19]. The similar rates of idiopathic epilepsy across studies suggest a common diagnostic trend. The differences in total seizure prevalence may reflect regional factors, such as referral patterns or access to diagnostic tools.

Previous studies have classified seizure types in two main groups: generalized and focal/non-generalized [15, 27]. Studies have reported that in cats, generalized tonic-clonic seizures account for 48%, whereas focal seizures represent 52% of cases [27]. In dogs, generalized tonic-clonic seizures have been identified in 81.1% of Poodles and 90.9% Dalmatians [15]. In this study, generalized tonic-clonic seizures were more frequent in both cats and dogs than in other seizure types. Seizures were recorded as generalized tonic-clonic in 83.3% of cats and 72.4% of dogs. Generalized tonic-clonic seizure is the most common seizure type in cats and dogs, and its prevalence has been reported to be 36–48% [15, 21, 27]. One possible explanation is the misclassification of focal seizures evolving into generalized seizures. Pet owners may not recognize subtle focal signs such as twitching, salivation or behavioral changes that precede generalization, especially if these occur rapidly. Furthermore, video recordings provided by owners may be incomplete or may begin after generalization has already occurred. Such limitations may contribute to the overestimation of primary generalized seizures in clinical records. In a similar study, it was reported that neurologists and non-specialists often differed in semiological classification when reviewing the same seizure videos [21]. This finding suggests that semiological classification is inherently subjective and may differ between observers. The objective method for determining whether a seizure is focal or generalized involves the recording and localization of epileptiform discharges using EEG. Despite this, EEG is not yet standardized in animals and remains challenging to implement in routine clinical practice. This situation has been discussed in IVETF and studies on the standardization of semiological classification are ongoing [2, 17].

Idiopathic epilepsy was identified in 41.7% of cats and 55.2% of dogs in this study. These findings are consistent with previous reports, which describe idiopathic epilepsy in 40–60% of dogs [8, 11, 18]. However, the proportion of structural epilepsy in cats (37.5%) was higher than that reported in earlier feline studies, which range from 18–30% [24, 27]. This increase may be attributed to the etiology of the cases included: among the nine cats diagnosed with structural epilepsy, seven were diagnosed with neurological FIP, and two with toxoplasmosis-associated encephalopathy. Seizures have been recorded in 19–25.5% of cats infected with FIP [4, 25, 30]. Neurologic FIP usually causes structural changes such as ventriculomegaly, syringomyelia and central vestibular syndrome that can lead to seizures [4]. Due to financial constraints, patients diagnosed with FIP could not undergo MRI and the structural factors causing seizures could not be identified. The high rate of FIP-related structural epilepsy in this study may be influenced by regional factors [1, 28, 32]. However, no published data are currently available to confirm an increased prevalence of FIP in this area. Further research is needed to investigate the local distribution of FIP and it is possible association with seizure disorders.

Among the dogs diagnosed with structural epilepsy, six were associated with CDV, one with bacterial meningoencephalitis, one with suspected hydrocephalus, and two with intracranial neoplasia. CDV is recognized as one of the most common etiological agents causing seizures in dogs under one year of age [23]. CDV is a neurotropic virus that induces demyelination and gliosis within neuronal tissue, leading to viral encephalitis. These structural changes in the central nervous system may result in the development of structural epilepsy [31]. In our study, CDV emerged as the most common etiology within the structural epilepsy group. This finding may be related to the regional epidemiology of CDV. In our region, legal regulations mandate rabies vaccination and sterilization for stray dogs prior to their release back to the streets; however, CDV vaccination is not routinely enforced [10]. A previous study reported CDV antibody prevalence of 9.03% among stray dogs in this area [27]. Several other studies have also demonstrated high CDV prevalence and insufficient immunization coverage, particularly in stray and shelter-housed populations [5, 20, 26]. This regional epidemiology may partly explain the higher proportion of CDV-associated encephalitis observed among structural epilepsy etiologies in our study compared to previous reports.

Age at seizure onset is an important criterion in the differential diagnosis of idiopathic epilepsy. According to the IVETF guidelines, the expected age range for idiopathic epilepsy is 1–5 years in cats and 6 months–6 years in dogs [2, 13]. In this study, the median age of cats diagnosed with idiopathic epilepsy was 2 years and 10 months, and for dogs, it was 5 years and 4 months—both within the expected ranges. However, four dogs were older than 6 years and one cat was older than 5 years. These age-outlier patients underwent Tier-II diagnostics, including MRI and/or CSF analysis, and no structural or metabolic causes were identified. In addition, interictal neurological examinations were normal and no triggering factors were present. In such cases, a diagnosis of idiopathic epilepsy remains justifiable when supported by comprehensive diagnostic work-up. These findings highlight the importance of integrating clinical signs, diagnostic tier level, and age when classifying epilepsy in veterinary patients.

Reactive seizures were diagnosed in 20.8% of cats and 10.3% of dogs in our cohort. These rates are consistent with previously reported prevalence ranges of 7.9–22% in cats and 10–11% in dogs [3, 14, 23, 27]. However, the median age of animals with reactive seizures in this study differed from earlier reports. The median age was 2 years and 7 months in cats and 11 years and 1 month in dogs. Previous studies reported median ages of 0.67 years and 2.9 years in cats, and 4 to 5.8 years in dogs [14, 23, 27, 33]. These discrepancies may reflect differences in etiological patterns, as reactive seizures can arise from a broad spectrum of causes, including intoxication, metabolic dysfunction, organ failure, and hormonal disturbances. Notably, intoxication has been identified as the most common cause of reactive seizures in cats, while metabolic (renal/hepatic encephalopathy) and hormonal (hyperthyroidism) etiologies also play an important role; the more heterogeneous distribution observed in our cohort is therefore consistent with this broader spectrum [14]. In our study, three cats were diagnosed with antiparasitic intoxication, while one had hyperammonemia and one had hyperthyroidism. Although intoxication has been reported as a predominant cause of reactive seizures in cats [14], our data suggest a more diverse etiological distribution. In dogs, reactive seizures were attributed to azotemia, hepatic encephalopathy, and multiple organ failure, without cases of intoxication. In contrast, intoxication has been reported as one of the leading causes of reactive seizures in dogs, yet the absence of such cases in our cohort is most likely attributable to the predominance of systemic/metabolic etiologies in our older patient population, as well as the tendency for acute intoxications to be managed at the primary care level before referral; additionally, the retrospective nature of our data may have resulted in underreporting of some intoxication cases [23, 33].

This study has several limitations. First, the relatively small sample size and its retrospective design may reduce the generalizability of the findings. Further studies with larger sample sizes in a prospective design may yield different or more conclusive results. Second, not all patients underwent Tier-II diagnostic evaluations such as MRI and CSF analysis due to financial constraints, potentially limiting the accuracy of etiological classification, especially in suspected idiopathic epilepsy cases. Third, the absence of EEG monitoring, which remains difficult to implement in veterinary practice, restricted the ability to objectively differentiate seizure types. Fourth, the study was conducted in a single veterinary center located in a specific geographic region, where the prevalence of diseases such as FIP and CDV may differ from other populations. These regional factors may have influenced the observed etiological patterns. Finally, although a three-step diagnostic approach similar to that used in dogs has been suggested for cats [12], no consensus has yet been established, and standardized guidelines remain lacking. In addition, certain seizure etiologies unique to felines, such as audiogenic reflex seizures (ARS), are not yet fully addressed within the IVETF classification system. This may limit the accuracy of etiological classification in feline patients and underscores the need for further research and updated consensus criteria in feline epileptology.

This study provides a comparative overview of the semiological and etiological classification of seizures in cats and dogs presented to a referral veterinary center. The findings confirm that idiopathic epilepsy remains the most frequent etiology in both species, although structural and reactive causes are not uncommon, particularly in older animals. The predominance of CDV among dogs and FIP among cats with structural epilepsy highlights the impact of regional disease prevalence patterns in Turkiye on etiological distribution. The high rate of generalized tonic-clonic seizures recorded in both species may reflect challenges in semiological classification, particularly in the absence of standardized EEG assessment. Despite diagnostic limitations, the application of IVETF-tiered criteria enabled structured classification of seizure etiology in the majority of cases. These results underscore the importance of a comprehensive diagnostic approach that integrates clinical history, neurological examination, and available diagnostics to improve diagnostic accuracy and therapeutic decision-making in clinical veterinary neurology.

CONFLICTS OF INTEREST

The authors declare that there is no conflict of interest regarding the publication of this article.