By Megan Davis, DVM and Jay McDonnell, DVM, MS, DACVIM
The Article: Clinical Characterization of Epilepsy of Unknown Cause in Cats. A.M.Wahle, et al. J Vet Intern Medicine 2104; 28: 182-188
This study tries to determine the prevalence of Epilepsy of Unknown Cause (EUC) in cats. Idiopathic epilepsy in dogs and humans is presumed to be genetic. [See Dr. McDonnell’s previous articles, Canine Epilepsy: An Information Guide and Geriatric Onset Ideopathic Epilepsy, for more on this subject.] However, causes for feline seizures haven’t been systematically reviewed.
Many times we falsely assume that a cat has “epilepsy of unknown cause” without a complete work-up and start anticonvulsants that simply treat the symptoms. The authors postulate that EUC is being overestimated in cats because a rigorous work-up is not followed. A typical recommended work-up needed for the diagnosis of EUC includes either a high field strength MRI scan or a post-mortem exam (PME). All of this is important because if we can diagnose a cause for the seizures, we can directly treat the cause, instead of treating the symptoms.
This retrospective study looked at data from 2005-2010 and included cats that had two or more seizures occurring on different days. Inclusion criteria were a full neurological examination, screening laboratory data and either a high-field MRI evaluation or postmortem exam (PME). EUC was defined as a patient with a normal neurologic exam, normal lab tests, normal cerebrospinal fluid (CSF), and no abnormalities on either MRI or PME.
Eighty-one cats met the inclusion criteria.
- Structural brain lesions noted in 38 cats on MRI or PME. This included tumors, meningitis, encephalitis, feline hippocampal necrosis and birth defects.
- In 25 cats, unequivocal metabolic /toxic abnormalities were found.
- In only 18 cats (22%) the cause of epilepsy was not found despite extensive diagnostic investigations (EUC).
- Neither sex nor age at seizure onset differed between the groups.
- The one-year survival rate for cats with EUC was 73% (13 of 18).
- 44% of cats with EUC experienced seizure remissions with anti-epileptic drug treatment.
- The one-year survival rate for NON EUC cats was 35%.
- EUC must be a diagnosis of exclusion of intracranial lesions and other causes. MRI is a crucial key to diagnosis.
Conclusion: The seizing cat is not the same as dogs with seizures. The vast majority of cats with seizures have an underlying cause that can be found with a neurologic work-up including MRI and spinal fluid analysis. Cats with EUC respond very well to anti-convulsants and have a higher survival than cats with identifiable problems.
The bottom line on seizures in cats…
At VNIoC we recognize that most cats with seizures have underlying disease that could and should be addressed. Cats with epilepsy of unknown causes do very well on anticonvulsants long term.