Steps Taken to Classify Seizures in Horses

Compared to what’s known about seizures in humans and small animals, there’s surprisingly little data about seizures in horses. In addition, veterinarians and owners use many different terms to describe the disorders. To further collective knowledge, a research team recently undertook a study aimed at better defining this relatively rare equine disorder.

Led by Véronique Lacombe, PhD, DVM, Dipl. ACVIM, associate professor at Oklahoma State University’s Center for Veterinary Health Sciences, the team studied information available for 104 horses admitted to The Ohio State University Veterinary Medical Center for seizures between 1988 and 2009.

Through the review, researchers were able to begin defining equine seizures and epilepsy, a chronic neurologic condition. Per the definition used in other species, epilepsy was defined as having two or more seizures. For the study, horses were considered epileptic if they had suffered two or more seizures at the time of admission to the hospital. Of the 104 horses, 70% were identified as having epilepsy.

In analyzing the available data, the researchers classified epilepsy in three categories: symptomatic, idiopathic, and cryptogenic. They diagnosed about a third of the horses with symptomatic epilepsy, meaning researchers identified a structural brain disorder (including tumors and other lesions) that caused seizures to occur.

The team determined that 2.7% of the seizures were caused by idiopathic epilepsy. These horses had a suspected genetic predisposition.

The third classification was cryptogenic epilepsy, meaning there were no identifiable causes. The researchers determined more than half the study horses (54%) had cryptogenic epilepsy because all their diagnostic test results were normal.

Additionally, the team found that horses with generalized seizures in which both sides of the brain were involved were seven times less likely to have epilepsy than those that had partial seizures, localized to one part of the brain.

Finally, researchers identified and classified "reactive seizures," which are seen in horses with normal brain function suffering from a temporary systemic disease, such as hepatic encephalopathy.

“It’s a first step in the classification of seizures and characterization of epilepsy in horses that could help veterinarians in establishing a diagnosis, therapeutic plan, and prognosis for seizures,” said Lacombe.

The study, "Epilepsy in horses: Aetiological classification and predictive factors," will be published in an upcoming issue of the Equine Veterinary Journal. The abstract is available online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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