Welcome to another "what-if" TidBit Tuesday! Here we go...
It's Wednesday morning and on your schedule is a 6 month old MC Cavalier King Charles Spaniel to see you for a complaint of "seizures". Upon examination, you find the pet to be normal both physically and neurologically. The client proceeds to describe the events that they've noticed as follows:
"When she goes to jump up on me to greet me she will sometimes fall into a praying position with all four legs stiff. It lasts 2-3 minutes and then she gradually relaxes and is able to walk normally."
Upon further questioning you discover that the dog appears mentally appropriate without signs of drooling, urinating, defecating or vomiting before or after the event. The client provides you a video of the event and at the conclusion, the dog resumes wiggling and excited behavior without obvious change in mentation. Hmmm....no preictal phase, no postictal phase and a relatively long ictal phase. Maybe it isn't an ictus at all???
Hopefully by now you're starting to think this may not be a seizure at all, but in fact one of those "movement disorders" you've been hearing about. What are they, and what can we do?
Movement disorders are a large group of diseases that are non-epileptic changes in muscle tone that happen episodically. They can be triggered by environment, or not. The most common classification that we see in veterinary medicine is a paroxysmal dyskinesia (PD), with or without dystonia. (I'm sorry...say what?? Okay, sorry. Paroxysmal = sudden violent or periodic event; dyskinesia = involuntary, erratic movements of muscles, usually face or limbs; dystonia = sudden muscle contracture, usually of opposing muscle groups which results in a writhing or twisting movement.) There are breed-specific PD which can be found here (https://www.frontiersin.org/files/Articles/163467/fvets-02-00065-HTML/image_m/fvets-02-00065-t005.jpg). Many of these are known to be inherited and some form of genetic mutation has been identified but in some cases we aren't clear on the cause. In humans there are inherited and acquired causes and entire books written about the different forms of movement disorders and their appearance. We don't have that...yet.
Pathophysiology
What happens to cause this, if it isn't a seizure? That is a complex question that I will try to answer simply. Most movement disorders originate from the brain in an area of the basal nuclei. This is where one of the most famous movement disorders, Parkinson's disease, originates from. Pathophysiology is largely unknown for animal movement disorders but there is definitely something going on in the basal ganglia. Diagnostic testing including brain MRI/CSF and at times muscle/nerve biopsies are recommended to pursue an acquired cause. These tests are often negative because inherited causes are more common.
Treatment
Effecting the basal ganglia through the use of benzodiazepine drugs (clonazepam 0.5 mg/kg) or even acetazolamide has shown some improvement. Some dyskinesia respond favorably to zonisamide and potassium bromide as well which further complicates our ability to decide cage-side if this is a seizure disorder, or not. An EEG is valuable here to identify the lack of brain changes consistent with seizures. However interpretation and acquisition of an EEG is challenging making this less available and useful for veterinary patients.
Sometimes it is plain ol' not clear if this is a seizure disorder or a movement disorder and we must do a trial and error with medications. In either case, breeding pets with known or suspected movement disorder OR epilepsy is discouraged due to the likelihood of inheritance.
Do you have a case in which you suspect a movement disorder? Let me know if you want to work through the case together! (Group frustration is much more tolerable than beating your head against the wall - metaphorically speaking - alone!).
Thanks for reading and have a great week! Stay safe, stay well and let me know how I can help you.