Diagnosis of epilepsy in canine and feline patients involves careful history taking, accurate physical and neurologic examinations, and appropriate diagnostic testing, including advanced imaging and cerebrospinal fluid analysis. Magnetic resonance imaging (MRI) is the gold standard for imaging brain tissue.
Unfortunately, this diagnostic procedure is an expensive test and does come with the risks inherent to anesthetic procedures. As clinicians, we have to be able to explain to clients the value of our recommended diagnostic tests while helping them weigh the risks versus benefits. The benefits of MRI are increased in patient populations which have diseases which may benefit from treatment beyond anticonvulsants. Current research suggests this is increasingly more true for feline epileptics compared to canine epileptics
Secondary epilepsy, defined as a structural forebrain lesion typically with an abnormal neurologic examination, is more commonly diagnosed in dogs greater than 6 years of age. In contrast, dogs who initially present with seizures between the ages of 1-6 are most likely to have primary epilepsy, where advanced imaging finds no structural abnormality. A 2017 study by Fredso et. al. found that 77.2% of their canine epileptics had no structural abnormalities on MRI.
Recent studies suggest this finding does not hold true in cats. There is a marked difference in the rates of diagnosed structural epilepsy in cats greater than 6 years of age when compared to cats between 1-6 years of age. It is also true cats in any age group are more likely than dogs to have structural causes of epilepsy. Some studies have demonstrated 41-62% of epileptic cats, without regard to age, have a structural brain lesion.
A recent retrospective study was published on cats suffering from epilepsy with no abnormalities on physical or neurologic examination during the interictal period. In this study (Raimondi et. al., 2015) MR imaging was reviewed for 188 of these cases. This study found cats who were older than 5 years of age and who otherwise had normal interictal neurologic examinations have an increased likelihood of demonstrating structural abnormalities on MRI as compared to dogs. Thus it is more important in cats to strongly consider MRI during an epileptic work-up. Clients should also be informed that even if their cat has no neurologic abnormalities during its interictal period, this current study suggests a higher incidence of structural abnormality in the brain of cats >5 years.
Magnetic resonance imaging of every feline epileptic is a goal we should be striving toward. Knowing the nature of each patient’s underlying cause of epilepsy will allow therapy to be better tailored to each patient. It will also allow the clients to be better informed about their pet’s condition and prognosis. Being able to justify the recommendation for advanced imaging will allow clients to play a more active role in their pet’s health care and increase their satisfaction with their pet’s overall care.