Introduction

• Definition: the term ‘dyskinesia’ is a Greek word literally meaning ‘bad movement’ with paroxysmal depicting the intermittent nature of the problem. Therefore paroxysmal movement disorders are a group of conditions characterized by episodes of abnormal movement in dogs and cats that are self-limiting with long periods of normality in between episodes.
• Cause: PD may be primary (ie they are of idiopathic or familial etiology) or secondary (ie resulting from drug-administration or a structural CNS lesion).
• Signs: episodic involuntary movements including:
  • Ballismus - abrupt contraction of limb muscles causing a flailing movement of the limb, this is often unilateral, as in hemiballismus).
  • Dystonia - sustained involuntary contraction of a group of muscles producing abnormal postures).
  • Chorea - abrupt, non-sustained contraction of different groups of muscles in the same patient).
  • Athetosis - prolonged contraction of trunk muscles causing a bending or writhing motion, this often accompanies chorea, thus described as choreathetosis).
• Diagnosis: is by inspection (ie observing a typical episode recorded by the owner) with clinical history and episode phenomenology being fundamental to this diagnosis.
• Treatment: medications used in the management of PD have variable and often limited efficacy. Some forms of PD have responded to diet (eg canine epileptoid cramping syndrome).
• Prognosis: although often refractory to medication, PD is non-progressive, benign and may be self-limiting.

Pathogenesis

Etiology

• Etiological classification is one method proposed to segregate PDs into their different types.
• Most PDs in people are classified as primary (ie they are of idiopathic or familial etiology, and are not part of a degenerative process).
• The term ‘primary’ is designated to PDs that are not associated with neurological signs between episodes and that have no evidence of pathological abnormalities.
• Other causes in people exist, eg secondary or symptomatic dyskinesias, ie those resulting from structural CNS lesions such as multiple sclerosis, head trauma, cerebral palsy, cerebrovascular accidents or encephalitis.
• Secondary PDs tend to be accompanied by additional neurological signs that are persistent between attacks.
• Not well defined with 2 main theories:
  1. A manifestation of transient dysfunction of the basal nuclei.
  2. PD is an epileptic disorder.

Predisposing factors

General

• PKDs are triggered by sudden movement in people.
• PNKDs usually occur in people spontaneously but can be precipitated by stress, tiredness or consumption of caffeine or alcohol.
• PEDs are characterized by attacks of involuntary movement that are induced by prolonged sustained exercise.
• Similar triggers are suspected in dogs but not proven.

Pathophysiology

• Although not fully understood, some of the specific breed related dyskinesias are slowly being defined.
• Canine epileptoid cramping syndrome is believed to be a manifestation of a gluten sensitivity with multi-system manifestations possible (eg signs indicative of dermatological or gastrointestinal disease).
• Episodic falling of the Cavalier King Charles Spaniel results from a microdeletion affecting the brevican gene (BCAN) which encodes the brain-specific extracellular matrix proteoglycan brevican:
  • Brevican belongs to the lectican family of aggregating extracellular matrix (ECM) proteoglycans, which comprises aggrecan, brevican, neurocan and versican.
  • The ECM complex at node of Ranvier is thought to play a pivotal role in maintaining a local microenvironment, acting as a diffusion barrier for K+ and Na+ around the perinodal extracellular space.
  • The disruption of ECM complexes governing synapse stability and nerve conduction velocity is likely to underlie the episodic falling phenotype.
• Soft coated Wheaten terriers suffer from a PD with a mutation in the PIGN gene:
  • The PIGN gene encodes glycosylphosphatidylinositol anchors that attach many different proteins to cell surfaces.
  • In people, this same mutation causes a distinct phenotype known as multiple congenital anomalies-hypotonia-seizures syndrome 1 (MCASH1).
  • To date, this mutation has not been associated with PD in people and the reason it causes PD in dogs is not understood.
• However, the pathophysiology of the large majority of PDs is not understood.

Timecourse

• Dogs may present as young as 3 months old up to 13 years of age.
• Episode frequency and duration is highly variable.

Diagnosis

Treatment

Prevention

Outcomes