Dystonia and Paroxysmal Dyskinesias: Under-Recognized Movement Disorders in Domestic Animals? A Comparison with Human Dystonia/Paroxysmal Dyskinesias

Abstract

Dystonia is defined as a neurological syndrome characterized by involuntary sustained or intermittent muscle contractions causing twisting, often repetitive movements, and postures. Paroxysmal dyskinesias are episodic movement disorders encompassing dystonia, chorea, athetosis, and ballism in conscious individuals. Several decades of research have enhanced the understanding of the etiology of human dystonia and dyskinesias that are associated with dystonia, but the pathophysiology remains largely unknown. The spontaneous occurrence of hereditary dystonia and paroxysmal dyskinesia is well documented in rodents used as animal models in basic dystonia research. Several hyperkinetic movement disorders, described in dogs, horses and cattle, show similarities to these human movement disorders. Although dystonia is regarded as the third most common movement disorder in humans, it is often misdiagnosed because of the heterogeneity of etiology and clinical presentation. Since these conditions are poorly known in veterinary practice, their prevalence may be underestimated in veterinary medicine. In order to attract attention to these movement disorders, i.e., dystonia and paroxysmal dyskinesias associated with dystonia, and to enhance interest in translational research, this review gives a brief overview of the current literature regarding dystonia/paroxysmal dyskinesia in humans and summarizes similar hereditary movement disorders reported in domestic animals.

A cross-species approach to disorders affecting brain and behaviour

“…Canine dyskinesias are primarily breed-associated disorders [65][66][67][68][69] ( Table 2) with signs that can be paroxysmal or constant (such as hypertonicity syndrome in Labrador retrievers) 66,69 . Causes of dyskinesias include degenerative or acquired disorders of the basal nuclei and upper brainstem (such as in Parkinson disease and Sydenham chorea in humans), suspected serotonin deficiencies within the spinal cord (such as in Scottish terrier cramps) and skeletal muscle ion channel abnormalities (such as in myotonia congenita) 65,67,68,70,71 . Examples of parallels between human and canine patients include orthostatic tremors in Great Danes that resemble primary orthostatic tremor in humans and dyskinesias in Jack Russell terriers and Labradors that mirror non-paroxysmal dyskinesias in humans.…”

“…Examples of parallels between human and canine patients include orthostatic tremors in Great Danes that resemble primary orthostatic tremor in humans and dyskinesias in Jack Russell terriers and Labradors that mirror non-paroxysmal dyskinesias in humans. Owing to our knowledge of canine genetics and the genetic homogeneity of inbreed strains, the study of domestic dogs can facilitate the identification of gene defects and mechanisms of inherited diseases 65 . For instance, a deletion in BCAN (encoding brevican core protein, a brain-specific protein involved in cell adhesion, axon guidance and neuronal plasticity) is associated with episodic falling in Cavalier King Charles spaniels.…”

Approach to canine paroxysmal dyskinesias

“…Differential diagnosis for PDs can include seizure episodes, neuromuscular disease, idiopathic tremors, tetanic spasms, narcoleptic/cataplexic disorders, vestibular attacks, syncopal episodes, acute pain syndrome, and paroxysmal behavioural episodes (Richter et al 2015). This list is by no means exhaustive and all of the above should be considered when making a diagnosis of PD.…”

“…There have been numerous published articles concerning PDs over recent years and the earliest report in veterinary literature dates back to 1942 concerning 'Scottie Cramp' in Scottish terriers (Klarenbeek 1942). Despite this, PDs remain a poorly understood and frequently under-recognised condition in veterinary patients (Richter et al 2015;Strain 2016). Some useful terminology when considering this subject is included in table one.…”

“…Dystonia tends to be the most common clinical sign which is characterised by sustained and often repetitive muscle contraction in one or several limbs (Lowrie & Garosi 2017). This results in abnormal postures or twisting and tremor-like movements (Richter et al 2015), which can initially appear confusing and alarming to owners and veterinary surgeons alike. Affected animals may collapse and become recumbent as a result of their dystonic movements, but they will frequently remain standing and responsive to their external environment (Platt 2016).…”