Tell me about cerebellar ataxia?

Cerebellar Ataxia: Clinical Overview

Cerebellar ataxia is a disorder of motor coordination resulting from cerebellar and/or brainstem dysfunction, manifesting as impaired voluntary movement control that persists regardless of visual input—distinguishing it from sensory ataxia. 1, 2

Clinical Manifestations

Core Motor Features

• Gait abnormalities: Wide-based, unsteady gait that does NOT worsen with eye closure (negative Romberg test) 2, 3
• Truncal ataxia: Difficulty maintaining posture, particularly prominent with cerebellar vermian pathology 1, 2
• Dysmetria: Overshooting or undershooting during finger-to-nose and heel-to-shin testing 3
• Dysdiadochokinesia: Impaired rapid alternating movements 1
• Dyssynergia: Loss of coordinated multi-joint movements 3

Speech and Ocular Findings

• Ataxic dysarthria: Scanning or slurred speech pattern resulting from impaired coordination (not weakness) of speech musculature 2, 3, 4
• Nystagmus and ocular dysmetria (saccadic overshooting) 3

Cognitive and Behavioral Features

• Cerebellar cognitive affective syndrome: Impaired executive function, visuospatial deficits, linguistic deficiencies, and inappropriate behavior—often overlooked by standard neurologic examination 5

Classification by Time Course

Acute/Subacute Ataxia (Hours to Days)

In children, postinfectious cerebellar ataxia accounts for approximately 50% of acute presentations to emergency departments 1, 2. Other critical causes include:

• Posterior circulation stroke: Requires immediate recognition due to mortality implications 2
• Acute cerebellitis: Presents with truncal ataxia, dysmetria, and headache; severe cases develop altered consciousness or increased intracranial pressure 2
• Miller Fisher syndrome: Classic triad of ataxia, areflexia, and ophthalmoplegia with anti-GQ1b antibody 1, 2
• Toxic/drug ingestion: Look for pupillary abnormalities 1, 3
• Brain tumors: Account for 11.2% of acute pediatric ataxia cases 1

In adults, vertebrobasilar insufficiency and posterior fossa hemorrhage are critical considerations 2.

Chronic/Progressive Ataxia (>2 Months)

Inherited causes predominate in chronic progressive ataxia:

• Spinocerebellar ataxias (SCAs): Autosomal dominant disorders with genetic heterogeneity and variable phenotypic expression; recent discoveries include RFC1 expansions causing CANVAS, FGF14-GAA causing SCA27B, and ZFHX3 expansions causing SCA4 1, 2, 6
• Friedreich ataxia: Major autosomal recessive form with associated spinal cord involvement 2
• Ataxia-telangiectasia: Look for characteristic telangiectasias on examination 2, 3

Acquired causes requiring urgent exclusion:

• Cerebellar tumors and brainstem gliomas: Must be ruled out early as they directly impact mortality 2
• Inflammatory/autoimmune disorders: Increasingly recognized as causes of sporadic ataxia 7
• Paraneoplastic syndromes 5
• Multiple system atrophy (cerebellar type) 7

Diagnostic Approach

Clinical Examination Priorities

Key distinguishing features to assess:

• Romberg test: Positive (worsening with eyes closed) indicates sensory ataxia involving dorsal columns, NOT cerebellar pathology 1, 2, 3
• Torticollis or neck resistance: Suggests craniocervical junction pathology, cord compression, or posterior fossa tumor 1, 3
• Associated signs: Motor spasticity or sensory ataxia warrants spine imaging in addition to brain imaging 2, 3
• Vestibular triggers: Lurching gait triggered by head rotation indicates vestibular (not cerebellar) dysfunction 1, 3

Neuroimaging Strategy

For acute ataxia: 2

• MRI head without IV contrast is the preferred initial imaging modality to exclude stroke, hemorrhage, infection, and mass lesions
• Add contrast if inflammatory or neoplastic causes are suspected

For chronic/progressive ataxia: 1, 2

• MRI head without IV contrast to detect cerebellar atrophy and signal changes
• MRI cervical and thoracic spine when spinocerebellar ataxias are suspected or spinal cord signs are present (spinal cord atrophy described in SCA1, SCA7, and other subtypes)

Critical caveat: Early imaging in hereditary cerebellar ataxias may be normal or subtly abnormal; serial imaging may be necessary to demonstrate progression 2.

Genetic Testing Approach

Modern diagnostic strategy includes: 6

• Targeted evaluation of short-tandem repeat (STR) expansions (SCAs, Friedreich ataxia, FXTAS, DRPLA)
• Next-generation sequencing (targeted panels, whole exome, or whole genome sequencing)
• Long-read sequencing shows promise for improving diagnostic yield

Common Pitfalls to Avoid

• Do not assume all progressive ataxia is benign hereditary disease—always exclude tumors, inflammatory conditions, and paraneoplastic syndromes first, as these are treatable and affect mortality 2
• Do not mistake weakness or hypotonia for ataxia in children; careful examination is required 3
• Do not overlook "pseudoataxia" from functional disorders that can mimic organic cerebellar disease 1, 3
• Do not rely solely on initial imaging in suspected hereditary ataxias—serial imaging may be necessary 2

Management Considerations

Symptomatic Treatment

• Balance training programs improve stability 3
• Postural training improves trunk control 3
• Task-oriented upper limb training improves reaching and fine motor control 3
• Speech and language therapy with intensive treatment targeting articulation, prosody, and intelligibility 4
• Assistive devices and orthoses improve balance and mobility 3

Disease-Specific Therapy

• Therapeutic agents under investigation are increasingly targeted to deleterious pathways, with most progress in Friedreich ataxia 7, 8
• Rare treatable forms exist and should not be missed 7