Non-Convulsive Seizures in Dogs and Cats With Cluster Seizures
This week we're going to dig into non-convulsive seizures in dogs a bit before we jump off of the seizure bandwagon and back into other topics in neurology next week. (Sorry to the surgeons that read these!) A recent study out of Germany by Tastensen et al (DOI: 10.1111/jvim.16953) evaluated nonconvulsive seizures in dogs and cats with cluster seizures. A few definitions, first....
Cluster seizures: 2 or more seizures within 24 hours in which pets regain consciousness between seizures.
Status Epilepticus (SE): Seizures lasting for longer than 5 minutes or 2 or more seizures in which consciousness is not regained.
Nonconvulsive seizures (NCS): no visible somatic or autonomic manifestation of seizures with evidence on EEG.
Nonconvulsive status epilepticus (NCSE): no visible somatic or autonomic manifestation of seizures, with evidence on EEG and the seizures are lasting longer than 5 minutes. (yikes!)
This study evaluated 26 dogs and 12 cats with EEG monitoring following cluster seizures and found 11 of the animals (9 dogs, 2 cats) had NCS. Of these 11 dogs and cats, 4 dogs and 2 cats (16%) had NCSE. They found repeated doses of benzodiazepine drugs and levetiracetam did not break the seizures. Only inhalant anesthesia with propofol induction resulted in a return to baseline EEG.
Six of 11 animals had a decreased level of awareness and a few of them had mild twitching of an ear which could have represented the somatic movement of the seizure. Sadly, this group had a much higher mortality rate (73% NCS; 67% NCSE) than the general population of dogs without NCS or NCSE (27%). Overall, cluster seizures have a higher mortality rate than for dogs or cats without cluster seizures (~40%) as well. None of these patients died as a result of NCSE or NCS however several were euthanized.
The seizure etiology was more often structural epilepsy (neoplasia, encephalitis, malformation, vascular cause or trauma) and accounted for 22/38 (58%) of the animals in the study. About 18% (7/38) had idiopathic epilepsy, 11% (4/38) had unknown epilepsy and about 18% (7/38) had reactive seizures. Does this mean that dogs and cats with structural epilepsy are more likely to have cluster seizures, or does it mean that the prognosis is inherently poorer for animals with structural epilepsy? If the prognosis is poorer, do clients elect humane euthanasia when in a situation of NCSE more readily, driving up the mortality rate, or does the disease make it harder to treat? Non-convulsive epilepsy is more common in humans with cluster seizures as well, and has a higher mortality rate than people without NCE or NCSE. I don't have the answers to these questions but pose them as a way of critically reviewing the data provided.
Take home message:
If you have a dog or cat with a history of cluster seizures and they are persistently, mentally inappropriate (obtunded, stupor or coma) after stopping the physical appearance of the seizure consider nonconvulsive seizures. Inhalant anesthesia would be recommended however without additional diagnostic testing (such as MRI or spinal tap) it would be unknown if there is high intracranial pressure from the underlying disease which could increase the risk of complication with anesthesia. So what do you do in general practice? If the owner wants a referral for 24 care - start there. If not, consider a bolus of diazepam or midazolam. OR you could monitor for 1-2 hours to determine if the change in behavior is secondary to postictal changes.
Not sure how to manage a seizure case? Feel free to email or call me or schedule a neurology consult! Please always text or call if it is an emergency; I don't check my email very often during the day. Have a great rest of your day!