Tremors, involuntary movements and paroxysmal disorders

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Involuntary movement abnormalities result in some of the most dramatic clinical presentations in veterinary medicine. Classically, involuntary movement disorders are present during periods of inactivity rather than during normal movement. Some involuntary movements are persistent whilst others are episodic. This chapter looks at types of involuntary movement, lesion localization, pathophysiology, differential diagnosis, neurodiagnostic investigation, localized tremor syndromes, generalized tremor syndromes, specific paroxysmal disorders.

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13.1 Lesion localization for tremors. The CNS (including the cerebrum, cerebellum and meninges) and the diffuse peripheral nervous tissue are highlighted. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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13.2 Dorsal view of the cerebellum, caudal brainstem and cranial cervical spinal cord. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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13.3 Magnification of the neuronal circuitry present in the cerebellum. The arrows indicate the direction of impulse transmission. Illustration created by Allison L. Wright, MS, CMI, Athens, Georgia, USA.
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13.4 Differential diagnoses for animals with abnormalities of movement and tone and localized and generalized tremors.
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13.6 Surface electromyogram (EMG) tracing of a normal dog, recorded when the patient was awake. Surface EMG tracing from the pelvic limbs of a dog with orthostatic tremors, recorded whilst the animal was standing.
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13.7 Sagittal T1-weighted MR image of the brain of a 6-year-old male castrated American Staffordshire Terrier with cortical degeneration. The cerebellar folia are clearly visible as a result of the CSF lying between them, reflecting the cerebellar atrophy.(Courtesy of N Olby)
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13.9 Sagittal T2-weighted MR image of a Bull Terrier with cerebellar vermal hypoplasia (arrowed). Dorsal T2-weighted MR image demonstrating replacement of the cerebellum with CSF (arrowed).
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13.10 Transverse contrast-enhanced CT image of the caudal fossa in a neutered 10-year-old Boxer bitch. There is a contrast-enhancing mass (*) compressing the dorsal cerebellum. The mass was removed surgically and confirmed to be a meningioma.
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13.11 Dorsal T2-weighted MR image of a Springer Spaniel with acute onset of cerebellar dysfunction. A well delineated hyperintensity (arrowed) is visible in the lateral hemisphere, which is compatible with ischaemic infarction.


Canine epileptoid cramping syndrome

A Border Terrier collapsing and exhibiting increased muscle tone and hyperkinetic movements. This condition is colloquially termed canine epileptoid cramping syndrome. (See page 248 in the Manual)

Dancing Dobermann

A young Dobermann with episodic flexion of the pelvic limb, which occasionally appears to be non-weight-bearing. This syndrome has been called dancing Dobermann disease. (See page 250 in the Manual)


A Bichon Frise exhibiting episodic spasticity of the pelvic limb, compatible with the dyskinesia described in this breed. The dog had a normal neurological examination in between the episodes. (See pags 233 and 234 in the Manual)

Episodic hypertonicity

A young Cavalier King Charles Spaniel with episodes of collapse. The syndrome seen in this breed is initially characterized by an increased stride length, especially in the thoracic limbs, leading to collapse. (See page 249 in the Manual)

Feline hyperaesthesia syndrome

A Domestic Shorthaired cat demonstrating signs compatible with feline hyperaesthesia syndrome. The cat seems irritated and restless and is focused on apparent 'discomfort' in the caudal spine. (Courtesy of C Chrisman) (See page 247 in the Manual)

Focal motor seizure

A Golden Retriever exhibiting intermittent involuntary movements of the head and neck muscles as a manifestation of a focal motor seizure. (See page 239 in the Manual)

Generalized tremor

(a) West Highland White Terrier exhibiting generalized tremors (previously termed white shaker disease). The dog has a mild ataxia, which can often be seen with this syndrome.

Generalized tremor

(b) A Pekingese exhibiting generalized tremors. The dog also has a mild left-sided head tilt, which is a feature of this syndrome. (Courtesy of Dr T Minami) (See page 245 in the Manual)

Idiopathic head tremor

(a) An English Bulldog with a paroxysmal head bob which does not affect the animal's level of awareness or ability to walk around.

Idiopathic head tremor

(b) A Boxer exhibiting a similar head bob to that seen in the English Bulldog, but this tremor began following an unremarkable anaesthetic episode (which can occasionally occur). Note how the tremor does not become more exaggerated or reduce in intensity when an attempt is made to distract the animal.

Idiopathic head tremor

(c) Idiopathic head tremors can be seen in any breed and can occasionally be in a lateral rather than vertical direction. (See pages 239 and 247 in the Manual)

Intention tremor

A young Domestic Shorthaired cat with cerebellar hypoplasia showing an intention tremor when fed. (See pages 233 and 242 in the Manual)

Myoclonus (1)

A Great Dane with canine distemper virus infection exhibiting myoclonus of the right thoracic limb. (Courtesy of Dr A Adeodato) (See page 232 in the Manual)

Myoclonus (2)

A Miniature Wired-Haired Dachshund with Lafora's disease showing myoclonic seizure events in response to auditory stimulation. (See page 232 in the Manual)

Myokymia and neuromyotonia

(a) A young Jack Russell Terrier with myokymia and neuromyotonia. The dog can be seen walking and playing. It is exhibiting some ataxia and a generalized increase in muscle tone. The dog also exhibits collapse and close examination of the muscles reveals the characteristic rhythmic, undulating muscle contractions.

Myokymia and neuromyotonia

(b) The tongue can be affected in animals with this condition. In addition, in this case vermiform movements can also be seen in the skin.

Myokymia and neuromyotonia

(c) The pharynx of dogs with myokymia and neuromyotonia can also exhibit the clinical signs seen in the skin.

Myokymia and neuromyotonia

(d) Electromyographic examination reveals neuromyotonic discharges. (Courtesy of Dr L Van Ham) (See pages 233 and 238 in the Manual)


A Dachshund is seen to collapse shortly after starting to eat due to narcolepsy–cataplexy. (See page 250 in the Manual)

Orthostatic tremor

A Great Dane exhibiting an orthostatic tremor. Note that dogs with this type of tremor can appear in discomfort when standing. The tremors disappear when the animal is not bearing weight. (See page 238 in the Manual)

Paroxysmal dyskinesia

A Chinook during a dyskinesia episode. Note the alert mentation along with the dystonic and athetotic-like movements. There appears to be mild dystonia in the face, as well as a mild dystonic head tremor. Towards the end of the clip, one pelvic limb appears to show ballism-type repetitive movements. Within the Chinook breed, episodes appear to show relatively consistent phenomenology. (Courtesy of R Packer) (See page 249 in the Manual)

Paroxysmal generalized rigidity

A young male Labrador Retriever with a paroxysmal generalized rigidity event. (Courtesy of L Garosi) (See page 249 in the Manual)

REM sleep disorder

A mixed-breed dog exhibiting several episodes of an REM sleep disorder. (Courtesy of T Schubert and C Chrisman) (See page 251 in the Manual)

Scotty cramp

A Scottish Terrier exhibiting pelvic limb gait abnormalities during exercise. The limbs demonstrate profound hypertonicity and progress to a bunny hop. The dog had moderate clinical signs compatible with Scotty cramp. (Courtesy of C Chrisman) (See page 248 in the Manual)

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