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Ataxia is incoordination caused by dysfunction to sensory nerve inputs, motor nerve outputs or the processing of them. It is not the result of muscular weakness. Ataxia is most often applied to unsteadiness in walking but it also refers to upper body incoordination and dysfunction in eye movements and speech.

Ataxia is common in multiple sclerosis but is also seen in several other conditions including diabetic polyneuropathy, acute transverse myelitis, vacuolar myelopathy, tumor or cord compression and hereditary forms of ataxia.

There are three types of ataxia, all of which are seen in MS:

  1. Cerebellar Ataxia
  2. This is caused by lesions in the cerebellum or in the parts of the brain that connect to it, such as the cerebellar peduncles, the pons or the red nucleus

    Because the cerebellum is responsible for synchronising voluntary muscle movement throughout the body, cerebellar ataxia can result in:

  3. Vestibular Ataxia
  4. In multiple sclerosis, vestibular ataxia is caused lesions to brainstem and the vestibular nuclei. In other conditions, it can also result from damage to the eighth cranial nerve leading from the balance organs in the inner ear.

    Vestibular Ataxia can result in:

  5. Sensory (Proprioceptive) Ataxia
  6. This results from dysfunction to position sensing (proprioceptive) nerve inputs. This means that the brain is confused as to the position of limbs.

    Sensory Ataxia results in:

This table shows the main characteristics of the three forms of ataxia (after Carlos Eduardo Reis):
  Cerebellar Vestibular Sensory
Dysarthria May be present Absent Absent
Nystagmus Often present Present Absent
Vertigo May be present Present Absent
Limb ataxia Usually present Absent Present(only in the legs)
Stance Unable to stand with feet together May be able to stand with feet together Able to stand with feet together and eyes open, but unable with eyes closed
Vibratory and position sense Normal Normal Impaired
Ankle reflexes Normal Normal Depressed or absent

Ataxia Links:

MedStudents - Neurology
Ataxias: Classification
Multiple Sclerosis Glossary: Ataxia
GeneClinics: Ataxia Overview
Movement, uncoordinated - Overview
Sensory: Large Fiber
Effect of Cannabinoids on Spasticity and Ataxia in Multiple Sclerosis

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