Atypical Seizures / Paroxysmal Dyskinesia
An episodic movement disorder that may be a form of focal motor seizure has been commonly recognized in Labrador Retrievers and other breeds (especially retriever crosses and poodles). This disorder has been variably called atypical epilepsy, paroxysmal dyskinesia or episodic dyskinesia.
We have recognized for some time that a significant proportion of Labrador retrievers with idiopathic epilepsy present either initially or during each episode with these atypical events and we have been collecting information (and DNA) from affected dogs for nearly 20 years. In three published reviews of Labrador Retrievers with epilepsy, focal motor seizures were described in 10 to 70% of the dogs.
Some Labradors with these atypical seizures simply stagger and look dazed or confused for a few seconds or minutes and then recover, without ever falling over. Others have a 2 to 5 minute episode (occasionally longer) where they appear anxious and are unable to stand erect and walk but they will attempt to crawl to their desired location. Some dogs will experience either uncontrollable trembling or increased muscle tone during an episode and a few simply develop a head tremor or trembling while they remain abnormally quiet and recumbent.
Affected dogs maintain consciousness and appear to be visual, able to recognize their owners and can even obey commands during the episodes. Episodes are most likely to occur when the dog is drifting off to sleep or when awaking from sleep in many dogs but exercise and excitement are common triggers in others. Affected dogs are normal between these episodes which occur suddenly, without warning. Systemic evaluation for metabolic, neoplastic and infectious causes of seizures is negative and repeated toxin exposure is unlikely. Related dogs may be similarly affected.
EEG evaluations of affected dogs have not been reported, and some investigators feel this is more correctly called a movement disorder (a dyskinesia) rather than a true seizure disorder. A similar syndrome identified in Chinooks (a Northern breed) has been identified as an inherited disorder and is thought to be a dyskinesia.
In support of this Labrador disorder being a seizure disorder, we have determined that many affected dogs will have a dramatic decrease in their episode frequency when treated with chronic oral anticonvulsant therapy and some affected dogs also develop more classical generalized tonic-clonic seizures later in life.