Initial Approach to Ataxia
The initial diagnostic approach to ataxia must be guided by temporal pattern: obtain brain MRI without contrast for acute ataxia (onset <72 hours) to exclude life-threatening causes like stroke, hemorrhage, or mass lesions; use CT head only when MRI is unavailable or when acute infectious causes are suspected; and obtain brain MRI with and without contrast for chronic progressive ataxia (>2 months) to identify tumors, inflammatory disorders, or inherited conditions. 1, 2, 3
Temporal Classification Determines Diagnostic Strategy
The first critical step is categorizing ataxia by onset pattern, as this fundamentally changes the diagnostic approach and urgency 4, 1:
- Acute ataxia: Symptoms developing within 72 hours 4
- Subacute ataxia: Symptom onset over more than one week 4
- Chronic progressive ataxia: Symptoms persisting >2 months (occasionally only weeks) 4
- Recurrent/episodic ataxia: Intermittent symptoms with normal examination between episodes 4
Acute Ataxia: Immediate Diagnostic Approach
Clinical Risk Stratification
The highest yield for urgent pathology occurs in children >3 years with symptoms >3 days duration and presence of extracerebellar symptoms (somnolence, encephalopathy, focal motor weakness, cranial nerve involvement). 4 In fact, 86% of children with significant neuroimaging pathology requiring urgent intervention had additional focal neurological findings beyond isolated ataxia 4.
Imaging Selection
Brain MRI without contrast is the first-line diagnostic test, detecting abnormalities in 64% of cases compared to CT's significantly lower sensitivity. 1 Specifically, MRI identifies abnormalities in 63.9% versus CT's 29.3% in acute/subacute ataxia 4. However, CT remains useful when MRI is unavailable or when acute infectious causes are suspected, as it can identify nontraumatic hemorrhage, hydrocephalus, cerebellar edema, and calcifications 4.
Common Etiologies by Frequency
The most common causes in acute ataxia are 4, 2:
- Infectious/postinfectious disorders (33.6%): Acute infectious cerebellitis, postinfectious cerebellar ataxia, acute disseminated encephalomyelitis 4, 2
- Brain tumors (11.2%): Require immediate neurosurgical consultation 4, 2
- Intoxications: Obtain toxicology screen 1
- Trauma (5%): Head trauma causing intracranial hemorrhage, contusion, or vertebral dissection 4, 2
Special Considerations for Acute Ataxia
In young children with acute cerebellar ataxia, recent viral illness, no extracerebellar signs, and negative urine drug screen, watchful waiting is acceptable with imaging reserved for clinical deterioration. 4 This approach recognizes that most acute childhood ataxia cases are transient and benign 4.
For trauma-related ataxia, obtain CT head emergently to assess for bleeding, mass effect, and herniation; add CTA head and neck if vertebral artery dissection is suspected. 4
Consider Miller-Fisher syndrome (characterized by ataxia, ophthalmoplegia, and areflexia) and order anti-GQ1b antibody testing. 4, 1
Chronic Progressive Ataxia: Systematic Evaluation
Imaging Protocol
Brain MRI without and with IV contrast is the definitive first-line study for chronic progressive ataxia, as it identifies cerebellar tumors, brainstem gliomas, inflammatory disorders, inherited ataxia patterns, and metabolic disorders. 3 The contrast is essential because cerebellar tumors and brainstem gliomas are collectively the most common causes requiring urgent intervention 3.
Additional Imaging Considerations
Add MR spectroscopy if metabolic disorder is suspected based on clinical presentation or initial MRI findings. 4, 3
Obtain MRI of the spine if there is concern for spinal cord involvement, such as in acute disseminated encephalomyelitis. 2
Consider MRA head and neck if posterior circulation stroke, hemorrhage, or vascular malformation is suspected, though stroke presents with ataxia in only 1-3% of cases. 4, 2
Laboratory Evaluation
Order comprehensive laboratory workup including toxicology screen, comprehensive metabolic panel, thyroid function tests, vitamin levels (B12, vitamin E), and infectious workup based on temporal pattern. 1 This addresses treatable causes like vitamin deficiency and autoimmune etiologies 5, 6.
Genetic Testing Strategy
For chronic progressive ataxia without identified acquired cause, proceed with whole-exome sequencing or comprehensive movement disorder panels rather than single-disease genetic testing. 1 Specific indications include progressive ataxia with family history, early-onset ataxia with dystonia, and chronic progressive ataxia without identified acquired cause 1.
Recurrent/Episodic Ataxia
Brain MRI without contrast is appropriate for recurrent ataxia to diagnose metabolic disorders and genetic abnormalities, and to establish normal neuroimaging supporting diagnoses like basilar migraine or benign paroxysmal vertigo. 4 There is insufficient evidence to support contrast-enhanced MRI in initial evaluation of episodic ataxia 4.
Add MR spectroscopy when underlying metabolic disorder is suspected (intermittent maple syrup urine disease, pyruvate dehydrogenase deficiency, Hartnup disease). 4
Clinical Examination Pearls
Cerebellar ataxia does NOT significantly worsen with eye closure, unlike sensory ataxia which shows positive Romberg test. 1 Document key cerebellar signs including wide-based gait, dysmetria, dysdiadochokinesia, and truncal instability, which persist regardless of visual input 1.
Critical Pitfalls to Avoid
Never delay MRI in favor of CT for chronic progressive symptoms, as CT misses the majority of posterior fossa pathology that MRI detects. 3 The sensitivity difference is substantial: 63.9% versus 29.3% 4, 3.
Never assume benign etiology without imaging in chronic progressive ataxia with nystagmus and dysarthria, as structural pathology must be excluded. 3
Never overlook treatable causes: Gluten ataxia accounts for 25% of sporadic ataxia cases, and immune-mediated ataxias are common 6, 7. Early identification and treatment can prevent progressive cerebellar degeneration 5, 7.
Acute Medical Management
For patients at high risk for space-occupying cerebellar infarction, implement aggressive supportive measures immediately: ensure sufficient cerebral oxygenation, treat hyperthermia aggressively, correct hypovolemia with isotonic fluids only, and maintain NPO status. 1
Management requires multidisciplinary collaboration between neurointensivists, vascular neurologists, and neurosurgeons, with early rehabilitation services involvement. 1