Classification of involuntary movements in dogs: Paroxysmal dyskinesias

Paroxysmal dyskinesias (PDs) are a group of hyperkinetic movement disorders characterised by circumscribed episodes of disturbed movement, superimposed on a background state in which such abnormality is absent. There is no loss of consciousness. Episodes can last seconds, minutes or hours, and the beginning and end of the movement disturbance are abrupt. Neurological examination is typically normal between episodes. PDs are associated with a broad spectrum of clinical presentations, encompassing various aetiologies. In humans, three main groups of PDs are distinguished, based on precipitating events rather than phenomenology: (1) paroxysmal kinesigenic dyskinesia (PKD); (2) paroxysmal nonkinesigenic dyskinesia (PNKD); and (3) paroxysmal exertion-induced dyskinesia (PED). In recent years, there has been an expansion of the spectrum of manifestations of PD due to the identification of genes associated with PD in humans (PRRT1, MR-1, SLC2A1 and KCNMA1) and dogs (BCAN and PIGN). The precise pathophysiological mechanism underlying the clinical manifestations of these reported mutations remains to be elucidated. Progress is also being made in the field of immunology, and links to gluten hypersensitivity in Border terriers with so-called canine epileptoid cramping syndrome (CECS) have been reported. This review aims to synthesise a classification scheme for veterinary PDs by reviewing human systems and applying them to veterinary examples. However, it is anticipated that genetic advancement will greatly aid in future stratification and therapy for PDs in dogs. Therefore, classification systems should be viewed as works in progress that should be modified as necessary.