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Ataxia is derived from the Greek word ataktos, meaning disorderly, irregular, or unruly. Specifically, ataxia refers to an abnormality of regulation of posture and movement, a disturbance of balance and gait. Although ataxia can be caused by peripheral sensory abnormalities, spinal cord lesions, or injury to cerebellar projections, this chapter will focus on symptoms, signs, and etiologies of cerebellar ataxia with an emphasis on infectious and postinfectious causes.

Ataxia is characterized by unsteadiness of gait, truncal instability, and incoordination of limb movements. Cerebellar ataxia may be accompanied by other symptoms of cerebellar dysfunction such as dysarthria. Key portions of the history that will guide the differential diagnosis and evaluation include the nature of the onset of symptoms (sudden or gradual), duration of ataxia (hours, days, or months), course of illness (static, episodic, slowly or rapidly progressive), and associated symptoms.

Abnormalities of gait are the most common presenting symptom. Toddlers may present for evaluation of refusal to walk, while older patients may report the sensation of walking on a moving train or boat; adults make comparisons to the sensation of alcohol intoxication. Patients have difficulty ambulating or making sudden turns without assistance; many experience falls due to the instability.

Patients may also present with problems of limb coordination. In particular, difficulties with fine motor skills should be sought on the initial history. Patients may report clumsiness or inability to perform activities of daily living such as eating, writing, or reaching for objects. Difficulties controlling movements or presence of an action tremor may also be described.

Nighttime or early morning awakening with headache, pain that is occipital in location, vomiting, or pain that worsens after lying horizontally, bending, or with cough, sneeze, or Valsalva maneuver suggests increased intracranial pressure.

Lethargy and somnolence are worrisome symptoms, highly suggestive of increased intracranial pressure from cerebral edema, hydrocephalus, or mass. Lesions of the brainstem may also produce alterations in mental status. One should inquire about brainstem localizing symptoms such as diplopia, vertigo, and dysphagia. Fever suggests an infectious etiology, but an infection involving the cerebellum could produce neurological symptoms in the absence of fever.

The differential diagnosis of ataxia is quite broad. We will review the differential diagnosis of ataxia according to the time course of presentation—congenital, acute monophasic, episodic or recurrent, and chronic progressive ataxia. Since most in-hospital evaluation for ataxia addresses acute monophasic ataxia, emphasis has been placed on this section.


Congenital ataxias are nonprogressive in nature but may become more evident over the course of the first 2 years of life as development progresses. They are typically related to malformations such as congenital cerebellar hypoplasia or dysplasia, or part of broader cerebral malformation syndromes such as Joubert or Dandy–Walker syndrome. Prenatal or perinatal injury, such as trauma or asphyxia, and hydrocephalus should also be considered. In contrast to acquired degenerative cerebellar ...

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