• Ataxia refers to incoordination of movement out of proportion to weakness.
  • Can be caused by dysfunction of cerebellum, proprioception, or vestibular system
  • Careful history of timing of onset and antecedent events key in framing differential: acute, subacute, chronic/progressive, episodic


  • Acute cerebellar ataxia (ACA) was previously seen in 1 per 5,000 cases of varicella, accounting for 25% of total cases. The risk following varicella-zoster virus (VZV) vaccination is 1.5 per 1,000,000 doses.
  • Most cases of ACA are still postviral, followed by ingestions, then Guillain-Barré syndrome (GBS) (combined account for 80% of total).
  • Dominantly inherited spinocerebellar ataxias (SCAs) are 1 to 5 per 100,000 but tend to have a later age of onset.
  • More likely to see autosomal recessive (AR) ataxias in childhood; most common is Friedreich ataxia (FRDA) at 1 in 30,000 to 50,000.


  • The cerebellum does not generate motor commands; instead, it modifies them to make them accurate and adaptive.
  • The cerebellum receives input from the vestibular apparatus, spinal cord, and the cerebral cortex (via the pons).
  • Both input and output is ipsilateral (i.e., right-sided cerebellar lesions cause right-sided ataxia).
  • Midline cerebellum (vermis) controls gait, head and trunk stability, eye movements; lesions of vermis result in wide-based (“drunken sailor”) gait, truncal sway, and head titubation (bobbling movements).
  • Cerebellar hemispheres control limb tone and coordination, motor learning, speech, eye movements; lesions of the cerebellar hemispheres cause limb dysmetria (trouble with finger-nose-finger testing).
  • Function can be impaired by chemicals, autoimmune processes, genetic mutations; typical pathologic finding is loss of Purkinje cells and injury to their elaborate dendritic arbor.


  • Acute onset
    • Ingestions/intoxications: alcohol, anticonvulsants including phenytoin, benzodiazepines, antihistamines, heavy metals, carbon monoxide
    • Infections (e.g., Bartonella, Mycoplasma, Epstein-Barr virus)
    • Postinfectious
    • Postvaccination
    • Demyelinating events: multiple sclerosis, acute disseminated encephalomyelitis (ADEM) (can be associated with altered mental status and seizure), Miller Fisher variant of GBS (triad of ataxia, ophthalmoplegia, areflexia; look for eye movement abnormalities and areflexia)
    • Initial presentation of recurrent ataxia
  • Subacute onset
    • Cerebellar hemorrhage
    • Ischemic stroke
    • Encephalitis or cerebellitis
    • Acute labyrinthitis/vestibular neuronitis (often prominent nausea/vomiting, hearing affected)
    • Posterior fossa tumors (e.g., medulloblastoma)
    • Paraneoplastic syndromes (opsoclonus-myoclonus syndrome, with multidirectional chaotic eye movements; evaluate for neuroblastoma)
  • Chronic or progressive
    • Developmental defects: Dandy-Walker syndrome, cerebellar agenesis, rhombencephalosynapsis, Chiari I malformation
    • Ataxic cerebral palsy
    • Tumors
    • Paraneoplastic
    • Metabolic/degenerative
      • With pathologic accumulation: hexosaminidase deficiency, Niemann-Pick type C, metachromatic leukodystrophy, Wilson disease
      • Hypomyelinating leukodystrophies (e.g., Pelizaeus-Merzbacher disease)
      • SCAs
      • AR ataxias including FRDA (associated pes cavus, cardiomyopathy, diabetes, polyneuropathy), ataxia telangiectasia (frequent infections, increased susceptibility to leukemia/lymphoma; telangiectasias are a late finding)
  • Recurrent
    • Migraine (Vestibular migraine can present with ataxia and vertigo without headache.)
    • Episodic ataxia (EA1 and EA2 best characterized, at least six loci identified)
    • Metabolic disorders: mitochondrial disorders, Hartnup disease, urea cycle defects, intermittent forms of maple syrup urine disease

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