O’Neill DG, Phillipps SA, Egan JR, Brodbelt D, Church DB, Volk HA. Epidemiology of recurrent seizure disorders and epilepsy in cats under primary veterinary care in the United Kingdom. J Vet Intern Med. September 2020.
While not common overall, seizures represent among the most prevalent neurologic abnormalities in cats, and occur in 2-3.5% of cats presented to referral hospitals. Recurrent seizure disorders (RSDs) include epilepsy and other conditions that lead to repeated episodes of seizure activity. Diagnosis of these conditions is confounded by inconsistent terminology around RSDs, including the use of epilepsy, idiopathic epilepsy, epilepsy of unknown cause, and genetic epilepsy, some of which have been defined in dogs but none consistently in cats. A further complication is that much of the data collected is from secondary and tertiary institutions, which, while more likely to gain a definitive diagnosis of cause, represented a limited and biased sample of the general population. The purpose of this study was to determine the prevalence of RSD and epilepsy in the wider cat population in the UK and to evaluate demographic risk factors for their occurrence. Secondarily, they aimed to assess factors associated with a diagnosis of epilepsy from the wider population of cats with RSD.
This study utilized the VetCompass database, which collects electronic medical record data from practices in the UK for epidemiologic research. It retrospectively recruited cats enrolled in the database over the course of 2013. Sample size estimates for prevalence were set at both 0.1 and 0.25% (quite conservative compared to canine prevalence of 0.82%), which indicated a samples size of 15,000-38,000 cats required to estimate prevalence to a precision of 0.05% with a 95% confidence level.
Inclusion for cases of RSD required at least one of: at least 2 episodes of seizure with a minimum of 24 hours between them; a final diagnosis of epilepsy in the medical record; or prescription of an antiseizure drug. Cats with extracranial reactive seizures (ie toxins or portosystemic shunts) were excluded. Candidate cases were generated via a computerized technical search of records, randomized, and manually reviewed for inclusion. Demographic factors including age, breed, sex, neuter status, coat color, weight, and others.
285,547 cats were enrolled in the study from 282 clinics. 1497 cats were identified as potential RSD cases, of which 458 were confirmed. This gave a 1-year prevalence of 0.16% of cats (note that this study enrolled all cats with RSD, not just new cases, as such measuring prevalence and not incidence). Of these cats, 114 (24.89%) were recorded as epileptic, a prevalence of 0.04% of cats. An additional 69 cases had a discussion of epilepsy recorded in the notes without an official diagnosis. There was no correlation between risk of RSK and purebred status. Median recorded age for first seizure event for all RSD cases was 8.9 years, while for the subset with epilepsy it was 6.4 years.
While univariate regression factors affecting the likelihood of RSD, only age and insurance status remained significant in multivariate regression. Odds of RSD increased progressively as cats aged, and insured cats had 1.5x the odds of RSD compared to uninsured. The same factors and general trends were identified for the risk of epilepsy in all cats, with the exception of cats aged 12-15 having decreased odds.
When assessing the risk of epilepsy in cats with RSD, only age 3-6 years was associated with an increased risk.
The increased odds of an RSD diagnosis in insurance cats is likely a result of increased diagnostics and workup in this portion of the population.
Some limitations to this study exist. Among them is the use of the term RSD rather than specific diagnoses of etiology. Confirmation of epilepsy was also made by primary practitioners and not neurologists, without the use of MRI or CSF analysis. While this was, in part, the goal of the study, it does somewhat limit epidemiologic analysis of the data and may have resulted in misclassification of cases. While relatively large and multi-centered, this study was also limited to the UK, which may limit generalizability to other parts of the world.
Overall this study provides good foundational data to suggest an overall RSD prevalence of 0.16% of cats in the UK, with 24.89% of them (0.04% of all cats) being classified by regular veterinarians as epileptic. Increasing age increased the risk of RSD, however, cats 3-6 years old had the highest risk of epilepsy. (MRK)
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