Contributors: Laurent Garosi, Simon Platt

 Species: Canine   |   Classification: Miscellaneous


  • Ataxia is defined as an uncoordinated gait and can be secondary to a lesion affecting one of three distinct anatomic regions of the nervous system:
    • A sensory peripheral nerve or spinal cord lesion (general proprioceptive ataxia).
    • A vestibular lesion (vestibular ataxia).
    • A cerebellar lesion (cerebellar ataxia).
  • Although some animals may exhibit ataxia that reflects a combination of these subclasses, accurate lesion localization is essential in establishing an appropriate list of differential diagnoses and a diagnostic plan.
Print off the owner factsheet on Incoordination - ataxia to give to your client.

Neuro-anatomical basis of ataxia

  • General proprioceptive (GP) ataxia:
    • Most common form of ataxia.
    • Results from lesion affecting the primary afferent neurons or the ascending proprioceptive tracts within the spinal cord and brainstem.
    • GP receptors are located within joints, muscles and tendons.
    • Changes in body position result in receptor discharge and stimulation of primary afferent (sensory) neurons. These primary neurons project to the spinal cord, where signals ascend through the dorsal columns and lateral funiculi to brainstem structures.
    • Animals with GP ataxia have additional neurological signs reflecting a spinal cord or brainstem localization.
    • Pathways of GP sensory system are anatomically adjacent to most of the upper motor neuron (UMN) pathways necessary for gait generation therefore the change in the gait generally reflects a combined dysfunction of both UMN paresis and GP ataxia (delayed onset of protraction of the limb and lengthened stride).
  • Vestibular ataxia:
    • Occurs with lesions affecting either the peripheral (receptor organ within the petrous temporal bone and vestibular nerve) or central vestibular (brainstem nuclei in the medulla oblongata, floculonodular lobe and fastigial nuclei in the cerebellum) apparatus.
    • Animals will often have concurrent neurological signs that reflect a vestibular disorder (eg head tilt or head sway, pathological nystagmus or positional strabismus).
    • Often broad-based gait with leaning towards the side of decreased vestibular tone.
    • Occasionally substantial swaying when walking and occasional falling.
    • Occasionally recumbent animal may be seen to roll.
    • Weakness or paresis is only seen with central vestibular disease and is not a feature of peripheral vestibular disease Vestibulocochlear neuritides.
  • Cerebellar ataxia:
    • Lesions within the cerebellar cortex.
    • Gait coordination relies on interaction between the cerebellum and motor systems.
    • Cerebellum controls the rate, range and force of movements, without actually initiating motor activity. It receives sensory input from proprioceptive, visual and auditory system. UMNs also project to the cerebellum and the cerebellum provides feedback information to UMNs in the brainstem and cerebral cortex via deep cerebellar nuclei.
    • Others signs of cerebellar disease (ie intention tremor) are often present Brain: cerebellar disease.
    • Cerebellar ataxia characterized by hypermetria (overflexion during limb protraction) and dysmetria (inability to regulate the rate, range, or force of a movement).

Neurological evaluation

  • The examination Neurological examination must first determine whether the gait abnormalities seen are truly indicative of ataxia. Lameness Lameness: general - investigation , various orthopedic gait disturbances and weakness due to non-neurological disease must be excluded. Posture and gait evaluation Gait analysis are evaluated first followed by postural reactions and cranial nerve testing to localize the lesion to the GP system, vestibular apparatus or cerebellum Cranial nerve neuropathy.
  • Posture evaluation and head position/movement:
    • Head tilt often indicates a unilateral vestibular disorder (peripheral or central).
    • Wide excursion of the head from side to side indicates bilateral vestibular disorder.
    • Intention tremor of the head indicates a cerebellar disorder.
  • Gait evaluation:
    • Leaning to one side or falling over indicates a unilateral vestibular disorder.
    • Symmetrical hypermetria on all four limbs or on one side and in the absence of paresis indicates a cerebellar disorder (or at least affecting the spino-cerebellar pathways in the spinal cord in the absence of other signs of cerebellar disorder).
    • Concurrent UMN paresis in limbs with no effect on the eyes or head posture indicates brainstem or spinal cord disorder Spinal cord diseases: overview.
  • Postural reaction testing:
    • Aims to detect subtle deficits that were not obvious on gait evaluation.
    • Can be abnormal with spinal cord, brainstem or central vestibular lesion.
    • Usually normal with peripheral vestibular lesion or cerebellar lesion.
    • Combined with gait evaluation, postural reaction testing helps to narrow down the lesion localization as being cranial to T3 spinal cord segments (all four limbs affected or both thoracic and pelvic limbs on the same side) or caudal to T3 spinal cord segments (both pelvic limbs or one pelvic limb affected) Neuroanatomical diagnosis.
  • Cranial nerve evaluation:
    • Presence of spontaneous or positional nystagmus indicates a vestibular disorder.
    • Vertical nystagmus or nystagmus that changes direction with different positions of the head indicates a central vestibular disorder.
    • Horner's syndrome Horner's syndrome can be associated with peripheral vestibular disorder secondary to otitis media interna Otitis media Otitis interna , nasopharyngeal polyps or middle ear tumor.
    • Absent menace response with normal vision and normal pupillary light reflex can be seen with ipsilateral cerebellar lesion.

Localizing the neuroanatomic lesion

  • Unilateral vestibular lesion:
    • Head tilt, leaning, falling or rolling.
    • Abnormal nystagmus.
    • Positional strabismus.
    • Presence of abnormal postural reactions and/or abnormal mentation and/or vertical or variable nystagmus and/or cranial nerve dysfunction other than facial nerve involvement suggests a central vestibular lesion.
  • Bilateral vestibular ataxia:
    • Crouched posture.
    • Reluctance to move.
    • Wide excursion of the head.
    • Presence of abnormal postural reaction and/or abnormal mentation and/or cranial nerve dysfunction other than facial nerve involvement suggest bilateral central vestibular lesion.
  • General proprioceptive lesion:
    • Concurrent UMN paresis in limbs.
    • Abnormal postural reactions.
    • No effect on the movement or position of the eyes or head posture.
    • Associated cranial nerve abnormalities and/or abnormal mentation suggests a brainstem lesion.
  • Cerebellar lesion:
    • Broad-based stance.
    • Symmetrical ataxia.
    • Hypermetria.
    • Truncal ataxia.
    • Intention tremor of the head.
    • Menace response deficit with intact vision.
    • No limb paresis.
    • Normal mentation.
    • Delayed then exaggerated response to postural reaction testing.

Differential diagnosis