Clinical characterisation of a novel paroxysmal dyskinesia in Welsh terrier dogs

Myotonia Congenita in Australian Merino Sheep with a Missense Variant in CLCN1

Myotonia congenita is a hereditary, non-dystrophic skeletal muscle disorder associated with muscle stiffness due to delayed muscle relaxation after contraction. We review myotonia congenita in domesticated animals and humans and investigated suspected myotonia congenita in a flock of Merino sheep in Australia. In 2020, a property in New South Wales reported a four-year history of lambs that would fall on disturbance before rapidly recovering, with 13 affected sheep identified in 2020. Episodes were associated with a short period of tetanic spasms and a stiff gait upon rising. Lambs were otherwise normal between episodes, although over time, lost body condition and occasionally died from misadventure. An inherited condition was considered from limited pedigree information and a preliminary diagnosis of myotonia congenita was made based on clinical presentation. Biochemistry from four sheep found variable, but typically mild increases in creatine kinase (CK) and aspartate aminotransferase (AST). Modified electromyography on six affected sheep found irregular electrical activity within the muscle. For four sheep, there were no consistent significant abnormalities on post mortem examination and histopathology-typical for this condition. A review of the Online Mendelian Inheritance in Man (OMIM) and Online Mendelian Inheritance in Animals (OMIA) databases was conducted to summarise information about myotonia congenita in humans and eight non-human species of animals. Comparing the characteristic clinical presentation, pathology and electromyography data of affected Merino sheep to similar conditions in other species assisted the identification of likely candidate genes. Whole genome sequencing of two affected lambs detected a missense variant in CLCN1 (NC_056057.1:g.107930611C>T; XM_004008136.5:c.844C>T; XP_004008185.4:p.(P282S)), with a predicted deleterious effect on protein function. An SNP genotyping assay was developed, and the variant segregated with the disease in 12 affected sheep and obligate carrier rams under an assumed recessive mode of inheritance. Identifying a likely causal variant and developing a diagnostic test allows screening of suspected affected or carrier Merino sheep for early intervention to reduce propagation of the variant within flocks.

Suspected paroxysmal dyskinesia in four small-breed dogs: Clinical presentation, diagnosis, management and prognosis

This case report details the clinical presentation, diagnosis, management and prognosis of paroxysmal dyskinesia (PD) in four small-breed dogs, each weighing under 6 kg: A 7-year-old spayed female Pomeranian, an 8-year-old female mixed breed, a 1-year-old female Pomeranian and a 9-year-old castrated male Poodle. These dogs were referred to our hospital due to movement disorders. Diagnosis was facilitated by video recordings of the episodes, assessing motor activity, consciousness, episode duration, any pre- or post-episodic behaviour as well as the presence of autonomic signs. Magnetic resonance imaging conducted on two of the dogs returned unremarkable results. Treatment trials included a gluten-free diet for all four dogs, with two also receiving acetazolamide. This intervention led to a decrease in the frequency of abnormal movement in all patients. Our findings suggest that PD in dogs can be effectively diagnosed through detailed symptom description using videos and questionnaires. Furthermore, once diagnosed, a combination of nutritional and medical management can be beneficial.

Canine paroxysmal dyskinesia-a review

Paroxysmal dyskinesias (PDs) are a group of involuntary, hyperkinetic movement disorders that recur episodically and may last seconds to hours. An important feature of PD is that there is no loss of consciousness during the episode. Using a clinical classification, three main types of PDs have been distinguished in canine PD: (1) paroxysmal kinesigenic dyskinesia (PKD) that commences after (sudden) movements, (2) paroxysmal non-kinesigenic dyskinesia (PNKD) not associated with exercise and can occur at rest, and (3) paroxysmal exertion-induced dyskinesia (PED) associated with fatigue. Canine PDs are diagnosed based on the clinical presentation, history, and phenomenology. For the latter, a video recording of the paroxysmal event is extremely useful. An etiological classification of canine PDs includes genetic (proven and suspected), reactive (drug-induced, toxic, metabolic, and dietary), structural (neoplasia, inflammatory, and other structural causes), and unknown causes. In this review, an overview of all reported canine PDs is provided with emphasis on phenotype, genotype, and, where possible, pathophysiology and treatment for each reported canine PD.

Dystonic head tremor in paroxysmal dyskinesia in 17 dogs (2021-2023)

BACKGROUND

Dystonia is a common component of the movement disorder paroxysmal dyskinesia (PD) in dogs. However, the incidence of dystonic head tremor (DHT) in these dogs has not previously been evaluated.

METHODS

The medical records of dogs presenting with PD between 2021 and 2023 were retrospectively reviewed, and those with available video footage and the presence of a head tremor were selected for further analysis.

RESULTS

Seventeen of the 39 (43.6%) dogs diagnosed with PD that had video footage available manifested DHT. Poodle or Poodle-cross was the most commonly affected breed (7/17). DHTs were described as fine irregular head tremors accompanied by cervical dystonia (17/17), truncal (11/17) or head (10/17) sway, shifting limb (10/17) or single limb (6/17) dystonia, freezing (8/17), ataxia (6/17), ptyalism (5/17), falling (5/17), kyphosis (4/17) and prayer posture (4/17). Neurological examination and advanced imaging, when available, were within normal limits.

LIMITATIONS

The limitations of the study include its retrospective nature, the lack of video recordings for all PD patients and the lack of electrophysiological evaluation of tremors and electroencephalography.

CONCLUSIONS

DHT exists in dogs with PD; it has characteristic features, and it should be considered in differential diagnoses for dogs with head tremors.

Dystonia in veterinary neurology

Dystonia is a clinical sign and main feature of many movement disorders in humans as well as veterinary species. It is characterized by sustained or intermittent involuntary muscle contractions causing abnormal (often repetitive) movements, postures, or both. This review discusses the terminology and definition of dystonia, its phenomenology, and its pathophysiology, and provides considerations regarding the diagnosis and treatment of dystonia in dogs and cats. In addition, currently recognized or reported disorders in dogs and cats in which dystonia is a particular or main feature are discussed and comparisons are made between disorders featuring dystonia in humans and animals. We suggest that when describing the phenomenology of dogs and cats with dystonia, if possible the following should be included: activity being performed at onset (e.g., resting or running or exercise-induced), body distribution, duration, responsiveness (subjective), severity, temporal pattern (i.e., paroxysmal or persistent, severity at onset and at later stages), presence or absence of autonomic signs (e.g., salivation), presence or absence of preceding signs (e.g., restlessness), presence or absence of signs after dystonia subsides (e.g., sleepiness), coexistence of other movement disorders, any other neurological manifestations, and possible links to administered medications, intoxications or other associated factors. We also suggest that dystonia be classified based on its etiology as either structural genetic, suspected genetic, reactive, or unknown.