- 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)
- 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
- With pathologic accumulation: hexosaminidase deficiency, Niemann-Pick type C, metachromatic leukodystrophy, Wilson disease
- Hypomyelinating leukodystrophies (e.g., Pelizaeus-Merzbacher disease)
- AR ataxias including FRDA (associated pes cavus, cardiomyopathy, diabetes, polyneuropathy), ataxia telangiectasia (frequent infections, increased susceptibility to leukemia/lymphoma; telangiectasias are a late finding)
- 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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