What is ataxia?

Understanding Ataxia

Ataxia is a neurological sign characterized by loss of coordination of voluntary muscle movements due to dysfunction in one or more components of the nervous system, manifesting as impaired coordination of movement, resulting in a wide-based, unsteady gait and poor coordination of the extremities. 1

Definition and Classification

Ataxia refers to incoordination of voluntary movements and can be classified as:

• Acute ataxia: Develops within hours or days (typically within 72 hours)
• Chronic ataxia: Persists longer than 2 months 1

Pathophysiology

Ataxia results from damage to several different nervous system structures, with common causes including:

1. Cerebellar damage: Affects coordination centers in the brain
2. Sensory pathway damage: Disrupts proprioceptive feedback

The underlying mechanism involves an inability to coordinate the relative activity of multiple muscles and adjust movements at joints for the effects of other moving joints (interaction torques). 2

Clinical Presentation

Key Features

• Unsteady, irregular stepping pattern
• Wide-based stance
• Variable step length and timing
• Lateral veering or swaying 1
• Incoordination of movement 3

Distinguishing Types

• Cerebellar ataxia: Symptoms remain consistent with eyes open or closed
• Sensory ataxia: Symptoms worsen when movements are made with eyes closed 2

Causes of Ataxia

Genetic/Inherited Causes

Ataxia can be part of numerous genetic syndromes including:

• Spinocerebellar ataxias
• Friedreich ataxia
• Ataxia-telangiectasia
• Fragile X-associated tremor/ataxia syndrome 4, 5

Genetic ataxias are very heterogeneous, with causative variants reported in over 50 genes, inherited in dominant, recessive, X-linked, or mitochondrial patterns. A common mechanism in dominant ataxias is repeat expansions. 5

Acquired Causes

• Mass lesions: Primary or metastatic tumors in the posterior fossa
• Vascular: Stroke, vasculitis (e.g., neuro-Behçet disease)
• Inflammatory: Acute cerebellitis, multiple sclerosis
• Paraneoplastic: Paraneoplastic cerebellar degeneration
• Toxic/Metabolic: Alcohol abuse, metronidazole toxicity, vitamin E deficiency
• Infectious: Bacterial cerebellitis
• Congenital: Chiari malformation, cerebellar hypoplasia 4

Clinical Evaluation

Neurological Examination

1. Coordination tests:

   • Finger-to-nose test
   • Rapid alternating movements
   • Heel-to-shin test 1

2. Gait assessment:

   • Observe for wide-based, unsteady gait
   • Evaluate for lateral swaying
   • Assess ability to walk tandem (heel-to-toe) 1

3. Balance testing:

   • Romberg test (standing with feet together, eyes closed)
   • Assessment of sitting and standing balance 1

4. Associated signs:

   • Nystagmus
   • Dysmetria
   • Hypotonia
   • Dysarthria (slurred speech) 1

Diagnostic Imaging

• MRI brain: Preferred modality for most ataxia evaluations, especially for suspected cerebellar pathology
• CT head with IV contrast: Alternative when MRI is contraindicated 4

Management Considerations

Based on the understanding of ataxia mechanisms, treatment approaches may include:

• Teaching patients to avoid rapid multijoint movements
• Encouraging slower movements limited to single joints
• Reducing movement complexity by minimizing the number of moving joints
• Stabilizing against inertial effects of limb movement 2

Common Pitfalls in Evaluation

• Inadequate assessment of other neurological signs (nystagmus, dysmetria)
• Failure to distinguish between cerebellar and sensory ataxia
• Not considering the effects of fatigue on examination findings 1
• Overlooking potential genetic causes when evaluating chronic progressive ataxia 5

For patients presenting with acute ataxia and suspected stroke, immediate imaging should be performed according to stroke protocols to avoid delays in appropriate care. 4