By Edward (Ned) E. Patterson, DVM, PhD
Vet Clin Small Anim 44(2014) 1103-1112.
Epilepsy is a disorder of the brain that is characterized by recurring, unpredictable seizures. The seizures are likely due to uncontrolled electrical activity in regions of the brain, which can produce behavioral changes. When no specific cause for the seizures can be found, the disease is known as idiopathic epilepsy (IE). Young dogs (less than 1 year of age) that experience seizures often do so because of exposure to an infectious agent or to a developmental anomaly. However, the seizures could also be due to an inherited degenerative disease or metabolic disorder. Most dogs that experience their first seizure when they are much older than 5 years of age most commonly do so because of a tumor, or a late-onset degenerative or metabolic disorder. IE is the diagnosis when a specific cause for the seizures cannot be found. It typically occurs in between these very early and late cases, with an age of onset between 1 and 5 years. IE is only diagnosed after all other causes of the seizure activity have been ruled out. Most dogs with IE have a normal lifespan. However, dogs that experience seizures lasting at least five minutes or who have multiple seizures without recovery in between (known as status epilepticus) typically have a reduced survival time.
Dr. Ned Patterson is an epilepsy clinician and researcher at the University of Minnesota Clinical Investigation Center. His Canine Epilepsy Network (www.canine-epilepsy.net) is a wonderful online resource for owners and breeders of affected dogs, as well as clinicians and researchers. He gave an excellent health seminar on epilepsy at the 2009 PBGVCA National in Tucson.
In this recent article, Dr. Patterson focuses on the need for urgent and aggressive treatment for seizures that last more than a few minutes or occur back-to-back without recovery. He cites the statistic that 40 to 60 percent of dogs with idiopathic epilepsy suffer cluster seizures or status epilepticus. These are emergencies that can lead to irreversible neuronal damage. Prolonged or frequent seizures can also lead to heart and kidney damage.
Dr. Patterson outlines the general standard of practice for canine status epilepticus. Unfortunately, there has not been an expert panel consensus statement for treatment of the canine disease, as there has been for human status epilepticus. Dr. Patterson states, “There does seem, however, to be fairly similar recommendations from a number of sources that can be generally summarized as:
“1. First-line therapy should be with a benzodiazepine, which most often is intravenous diazepam, but can be by other routes and/or with midazolam, or lorazepam. There have not been any published studies comparing benzodiazepines to each other in dogs or cats as there has been for people. Shortly after the benzodiazepine, there should be intravenous loading or mini loading doses of intravenous phenobarbital or intravenous [levetiracetam] to start chronic therapy, for when the short-acting benzodiazepines wear off.
“2. In second-line therapy for continuing seizure activity, intravenous phenobarbital or intravenous LEV or a [constant rate infusion] of diazepam or midazolam should be given. The author has found that two or more of these second-line therapies can potentially be given to the same patient.
“3. Third-line therapy of [refractory status epilepticus] to induce general anesthesia can be with intravenous propofol or pentobarbital. In some instances, IV ketamine or inhalant anesthesia has been administered.”
Research over the past decade has tested new approaches, which Dr. Patterson hopes will lead to paradigm shifts in treatment for seizures. These include neurosteroids, gene therapy, use of molecules that alter gene expression, and new biochemical targets. Dr. Patterson concludes, “Status epilepticus in companion animals is an emergency and should be quickly treated by recommended first-line (emergent) therapy with benzodiazepines followed by loading doses of chronic therapy drugs, and then secondline, and third-line (refractory) therapy when needed. Cluster seizures can evolve into status epilepticus, and therefore at-home treatment with per rectum or intranasal benzodiazepines and longer-acting oral antiepileptic drugs for dogs is often recommended, and if not effective, then hospitalization for observation and treatment as for status epilepticus are recommended.”