TABLE 1.

Terminology used to describe clinical signs commonly associated with paroxysmal dyskinesia, and adaptations for veterinary use

Athetosis	Prolonged slow involuntary contraction of the trunk muscles resulting in nonrhythmic bending/sinuous/writhing movements that preclude maintenance of a stable posture. Greek origin is defined as “without position or place”. Athetosis is often seen with concurrent choreatic movements (ie, choreoathetosis). Athetosis typically involves distal limb muscles (less frequently trunk, face, neck). Whereas individual choreatic movements may be distinguished from one another as discrete movements, athetotic movements generally seem to “flow” from one to another and are more difficult to separate from each other. May occur at rest or may be worsened or precipitated by movement. Due to differences in anatomy and degrees of freedom of joint motion between humans and canines (with canines lacking complex movement of the fingers/hands/wrist), athetosis is difficult to distinguish from chorea and ballism, and should be described simply as dyskinesia.
Ballism	An abrupt involuntary contraction of proximal limb muscles (eg, shoulders) resulting in large‐amplitude flailing/flinging movements of the limb(s); typically unilateral. May be indistinguishable from chorea/athetosis in animals.
Chorea	An abrupt (ie, jerky), irregular (ie, nonpatterned), and unsustained low‐amplitude contraction of muscle groups, particularly distal muscles (+/− shoulders, hips, face less frequently) resulting in 1 or more discrete movements. Similar in distribution to athetosis but faster and larger amplitude. From the Latin word “choreus” (ie, dance). May appear similar to movements associated with restlessness. Not characterized by an inserted posture (as in dystonia) but rather an inserted movement. Similar to athetosis, chorea in dogs is difficult to distinguish from athetosis and ballism and should be described simply as dyskinesia.
Cramp	A sudden, severe, and involuntary muscle contraction or over‐shortening that is generally temporary and benign. 10 Can cause mild‐to‐excruciating pain, and immobility of the affected muscle(s). Onset is usually sudden, and resolves on its own over a period of several seconds, minutes, or hours.
Dystonia	A sustained, slow, involuntary contraction of agonist and antagonist muscles of a body region producing abnormal postures and/or involuntary movement of portions of the body along a longitudinal axis. May appear as a twisted posture of the limbs, trunk, or neck. Dystonia may create new movement or may inhibit it by inserting an abnormal posture in place of the intended movement (see below for further classification). Associated with varying durations of muscle contracture (arrhythmic). May be prolonged/sustained (as in neuromyotonia) or transient. Typically does not involve rapidly alternating contraction/relaxation, as occur in tremor and myoclonus, although these movements may occur coincidentally. Postures adopted vary, but are largely stereotypical (ie, predictable/patterned) for each individual. Frequently triggered by movement, standing, or by adopting particular postures. Only occurs in wakeful state. Does not necessitate concurrent hypertonia; may only produce sufficient contraction of muscles to allow resistance to gravity (Video S1).
Fasciculations	A brief spontaneous contraction resulting from the spontaneous activation of a small number of muscle fibers, often causing a flicker/vermicular movement under the skin. 10
Myoclonic tremor	Likely replaced by term rhythmic myoclonus: brief shock‐like myoclonic movements occurring with a defined unidirectional fast phase (positive or negative) and a slower recovery phase.
Myoclonus	A sequence of repeated, variably rhythmic, brief shock‐like jerks resulting from the sudden involuntary contraction or relaxation of 1 or more muscles. Generates movement of the affected body part (ie, overall limb/head movement), whereas tremors, myokymia, neuromyotonia do not. 11 Differs from a startle response in that myoclonic movements frequently occur independent of a sudden stimulatory input and occur repetitively. May be precipitated or worsened by movement, stress. May occur during sleep.
Myokymia	A focal or generalized continuous contraction of facial or limb myofibers, often exhibiting an undulation/vermicular movement of the skin overlying the affected muscle (ie, as if worms were crawling under the skin) (Video S2).
Myotonia	A disturbance in muscle relaxation after voluntary contraction or percussion. Is most noticeable after a period of rest, and improves with continued activity. Frequently results in noticeable hypertrophy of the affected muscles and may lead to diminished joint flexion when walking (ie, “stiffness” in the limbs) (Video S3).
Neuromyotonia	A more severe form of myokymia, seen as persistent muscle stiffness and delayed muscle relaxation due to abnormal electrical discharges of motor nerves. Distinguished from myokymia in that it results in generalized muscle stiffness with delayed relaxation, often resulting in collapse. Both may occur simultaneously. Clinically results in noticeable muscle rippling. May be precipitated by stress and/or excitement (Video S4).
Overflow movement	“Spread” of movement beyond an area of (unintended) movement to a nearby/adjacent area, due to presumed local spread of motor command.
Tetanus	Severe, sustained muscle contraction resulting from impairment of glycine release within the ventral gray matter of the spinal cord resulting from exotoxin release associated with Clostridium tetani infections.
Tetany	Sustained muscle contraction, usually involving extensors muscles. No relaxation is noted. May be accompanied by sensory changes (eg, hypocalcemia‐induced tetany).
Tremor	Involuntary, rhythmic oscillatory movements of a body part with symmetric velocity in both directions of movement (i.e. sinusoidal), around a joint axis. Frequently caused by rhythmic alternating contractions of agonist and antagonist muscles. May be present alone or concurrently with other movements. Tremors can be subdivided as follows: rest tremor, postural tremor, action tremor; intention tremor. See below for further classification.