The term paroxysmal dyskinesias encompasses a rather heterogeneous group of movement disorders, characterized by limb dystonia and other signs, such as rapid and sudden movements caused by short-lived muscle contractions, abnormal postures, and contortions due to contraction of trunk muscles and limb instability.
In dogs, these disorders take on breed-specific forms: in fact, the signs by which they manifest themselves, the age of onset and the course are usually different in the different breeds in which they have been recognized.
In some cases a genetic mechanism of transmission of certain paroxysmal dyskinesias has been identified, and in general a hereditary basis has been hypothesized.
Delving deeper into the clinical features with which these disorders manifest in the specific breed would allow for a better understanding of their causes and the identification of the most useful genetic analyses.
The study in Welsh terriers
In a retrospective study conducted at a veterinary center at the University of London, clinical data of five Welsh terrier breed dogs visited at the center between 2013 and 2018 for episodes suggestive of paroxysmal dyskinesia never previously detected in this breed were studied.
The main objective was to describe the clinical features, define the course, and estimate the prevalence of this disorder in Welsh terriers.
The five dogs were identified based on medical records and video footage taken during the paroxysmal episodes, which suggested a possible diagnosis of paroxysmal dyskinesia based on the presence of certain signs: abnormal and involuntary movements Causing contortions or sudden and repetitive movements of the limbs, trunk, or neck, and/or muscle contractions that led to abnormal postures, without signs of seizure activity.
Comprehensive clinical and neurological examinations were performed for all dogs, which revealed no abnormalities. Imaging investigations of the brain and cerebrospinal fluid with MRI were also performed in three cases, which showed dilatation of the lateral ventricles, mild in one case and moderate in the other two.
In all dogs, the episodes were characterized by dystonia with dyskinesia, without loss of consciousness or autonomic signs. No clinical factors or special events were found to be correlated with the onset of the paroxysmal episodes, which occurred at a median age of 31 months; the frequency between episodes was highly variable across subjects, and among the events the dogs appeared normal.
In addition, to assess the presence of these episodes and define their characteristics in a larger population, 177 Welsh terrier dog owners completed an online questionnaire, with the aim of collecting data on the animals and their medical history and identifying signs of paroxysmal dyskinesia based on an explanatory video.
Signs of paroxysmal dyskinesia were detected in 41 dogs (22.8%), based on the characteristics of the episodes: sustained hypertonia of the limbs with periods of flexion (35 dogs, 85.4%), abnormal body posture with lateral flexion of the neck and spine (15 dogs; 36.6%), kyphosis (7 dogs, 17.1%), and abnormal head posture (4 dogs, 9.8%); no cases reported loss of consciousness.
The median age of onset was 59 months, while the frequency of events varied widely, as did the duration of a single episode: from 30 seconds to 30 minutes, with a median value of 3.5 minutes. In the majority of cases (32 dogs, 78%), it was not possible to identify a determining factor for the onset of the episodes; in the other cases, the events seemed to be associated mainly with stress, arousal or exercise.
How to evaluate the results
“This study offers the first clinical characterization of a new type of paroxysmal dyskinesia in the Welsh terrier breed. The episodes are characterized in most cases by dystonia, with altered posture, and/or other signs of dyskinesia, with abnormal, involuntary, repetitive movements of the limb, trunk, or neck, without loss of consciousness or autonomic signs during the events,” the study authors comment.
“The prevalence identified is consistent with an inherited etiology, but further studies are needed to confirm the heritability of the disorder and determine the presence of a potential underlying genetic cause.”
Whittaker DE, Volk HA, De Decker S, Fenn J. Clinical characterization of a novel paroxysmal dyskinesia in Welsh terrier dogs. Vet J. 2022 Feb 9:105801.