Acute and chronic ataxia

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Coordination depends on the cerebellum, proprioceptive pathways, vestibular system, vision and motor output. Cerebellar ataxia is present with eyes open and closed and often affects eye movements, speech and limb targeting. Sensory ataxia becomes markedly worse when vision is removed and accompanies impaired distal proprioception. Vestibular disease causes motion illusion and postural imbalance, often with autonomic symptoms. Frontal gait apraxia, parkinsonism, weakness, orthostatic hypotension and functional gait disorder can mimic ataxia and should be identified through positive clinical features.

Tempo narrows the differential. Seconds to hours suggests stroke, haemorrhage, seizure-related dysfunction, toxin or acute metabolic disturbance. Days to weeks raises inflammation, infection, nutritional deficiency, medication accumulation, paraneoplastic disease or tumour. Months to years suggests alcohol-related degeneration, multiple-system atrophy, spinocerebellar ataxia, Friedreich ataxia, CANVAS, mitochondrial disease or another inherited syndrome. Stepwise worsening may represent repeated vascular events or demyelination.

Assessment begins with safety and function: ability to sit, stand, swallow and mobilise; falls and driving; cognition; autonomic symptoms; hearing and vision. Examine eye movements, nystagmus, speech, tone, power, reflexes, plantar responses, sensation, heel–shin and finger–nose testing, rapid alternating movements, stance and gait. MRI is central for non-obvious cerebellar disease, but urgent CT and CTA may be faster for acute stroke. Results should lead to cause-specific treatment, physiotherapy, occupational therapy, speech and language support and genetic counselling when appropriate.

Key points

Ataxia is impaired coordination not explained by weakness alone; localise it as cerebellar, sensory, vestibular or mixed before constructing the differential diagnosis.
Sudden ataxia, severe gait inability, new headache, diplopia, dysarthria or focal signs is posterior circulation stroke until urgently assessed with brain and vascular imaging.
Cerebellar disease produces broad-based gait, truncal instability, dysmetria, intention tremor, dysdiadochokinesia, gaze-evoked nystagmus and scanning or slurred speech.
Sensory ataxia accompanies loss of joint position or vibration, pseudoathetosis and a positive Romberg sign; vision improves stance because proprioceptive input is impaired.
Vestibular imbalance is dominated by vertigo, oscillopsia and nystagmus, with veering or falling; central eye signs or inability to stand requires urgent stroke expertise.
Acute toxic and metabolic causes include alcohol, sedatives, antiseizure toxicity, lithium, hypoglycaemia, electrolyte disturbance and thiamine deficiency; medication and exposure history is essential.
Subacute progression raises immune, paraneoplastic, nutritional, infectious and structural disease, whereas long progression suggests genetic or degenerative ataxia but treatable causes still need exclusion.
MRI, targeted blood tests, neurophysiology, CSF and genomic testing should follow tempo, localisation and family history; indiscriminate panels create incidental results without replacing neurological assessment.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Vascular and structural disease

Sudden cerebellar or brainstem infarction and haemorrhage cause acute ataxia, while tumour, hydrocephalus or compression more often produces progressive imbalance with additional focal or pressure features.

Toxic, metabolic and nutritional causes

Alcohol, sedatives, antiseizure medicines, lithium, hypoglycaemia, electrolyte disturbance and thiamine deficiency can impair coordination; exposure history and systemic physiology often identify a reversible cause.

Inflammatory, infectious and paraneoplastic disease

Demyelination, cerebellitis, systemic autoimmunity, infection and cancer-associated immune syndromes commonly evolve over days or weeks and may add encephalopathy, fever, neuropathy or other neurological deficits.

Genetic and degenerative disorders

Spinocerebellar ataxias, Friedreich ataxia, RFC1-related disease and multiple-system atrophy usually progress over months or years; pedigree, neuropathy, vestibular and autonomic findings refine the group.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Network input disruption
Disease interrupts cerebellar circuitry or the proprioceptive and vestibular inputs that normally report limb position, head movement and balance to central motor networks.
2
Impaired error correction
The nervous system cannot compare intended with actual movement accurately, producing dysmetria, decomposition, intention tremor, dysdiadochokinesia and poorly timed eye or speech movements.
3
Postural compensation failure
Inaccurate limb and body-position signals destabilise stance and gait. Visual input can partly compensate for sensory ataxia, whereas cerebellar incoordination persists with eyes open.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Cerebellar hemisphere syndrome

Ipsilateral limb dysmetria, decomposition, intention tremor and dysdiadochokinesia predominate when a cerebellar hemisphere or its connections are affected.

Vermian or midline syndrome

Truncal titubation, broad-based stance and severe gait instability can dominate with relatively preserved limb coordination in midline cerebellar disease.

Sensory ataxia

Loss of vibration and joint position, depressed reflexes and marked worsening with eye closure points towards large-fibre neuropathy or posterior-column disease.

Central vestibular syndrome

Direction-changing or vertical nystagmus, skew deviation, severe truncal ataxia or an additional focal sign supports brainstem or cerebellar pathology.

Toxic phenotype

Symmetric gait and limb ataxia with drowsiness, dysarthria or nystagmus after a medicine change, overdose or alcohol exposure suggests reversible toxic dysfunction.

Multisystem inherited pattern

Neuropathy, deafness, retinal disease, pyramidal signs, cardiomyopathy, diabetes or a family history can identify a genetic ataxia category and guide testing.

Red flags requiring action

Abrupt onset, new severe headache, focal weakness, dysarthria, diplopia or inability to stand requires immediate posterior circulation stroke assessment.
Falling consciousness, repeated vomiting or progressive headache with cerebellar signs raises haemorrhage, hydrocephalus or posterior fossa mass effect.
Ataxia with confusion, ocular motor abnormality, malnutrition or alcohol dependence is possible Wernicke encephalopathy and needs immediate parenteral thiamine.
Fever, meningism, immunosuppression or rapidly progressive encephalopathy requires urgent assessment for infection or immune-mediated cerebellitis.
Rapid progression over weeks, weight loss or systemic cancer clues warrants expedited neurological and malignancy evaluation for paraneoplastic or structural disease.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
CT brain and CT angiographyFirst step
Why
Exclude haemorrhage and identify vertebrobasilar occlusion or dissection during sudden-onset ataxia.
Interpretation and limitations
Early posterior fossa infarction may be invisible on non-contrast CT; a normal scan does not end the acute stroke pathway when examination remains concerning.
02
MRI brain with diffusion-weighted imaging
Why
Detect cerebellar or brainstem infarction, demyelination, tumour, inflammation and patterns of cerebellar atrophy.
Interpretation and limitations
Small acute posterior lesions can initially be diffusion-negative, and atrophy distribution is a clue rather than a single definitive genetic diagnosis.
03
Targeted blood profile
Why
Find glucose, electrolyte, liver, thyroid, B12, folate, vitamin E, inflammatory, coeliac or other reversible contributors.
Interpretation and limitations
Choose tests from tempo, diet, surgery, alcohol and systemic features; borderline results require functional or confirmatory interpretation rather than automatic attribution.
04
Medicine levels and toxicology
Why
Identify lithium, phenytoin, sedative, alcohol or other drug-related cerebellar toxicity when exposure is plausible.
Interpretation and limitations
Relate levels to timing, albumin, renal function and clinical toxicity; a therapeutic total concentration can mislead when protein binding or interactions are abnormal.
05
Nerve conduction studies
Why
Characterise a large-fibre sensory neuropathy contributing to sensory ataxia and refine inherited or acquired causes.
Interpretation and limitations
Normal routine studies do not exclude small-fibre disease or dorsal-root ganglionopathy, and examination should determine whether neuropathy truly explains the gait.
06
Lumbar puncture
Why
Assess inflammatory, infectious, malignant or selected immune-mediated causes after imaging and specialist review.
Interpretation and limitations
Do not perform before excluding posterior fossa mass effect or another contraindication; cell count, protein, oligoclonal bands and antibodies need a specific diagnostic question.
07
Genomic testing
Why
Diagnose a hereditary ataxia when age, phenotype or family pattern supports it and the result will alter counselling or care.
Interpretation and limitations
Repeat expansions may require assays not detected by routine sequencing; arrange testing through clinical genetics with pre-test discussion and current NHS genomic criteria.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Sensory ataxia

Loss of vibration and joint position, pseudoathetosis and marked worsening on eye closure favour peripheral nerve or dorsal-column disease over a primary cerebellar lesion.

Peripheral vestibular disorder

Vertigo, oscillopsia and unidirectional nystagmus with preserved limb coordination support vestibular disease; central eye signs or inability to stand should prompt urgent stroke assessment.

Weakness or parkinsonian gait

Pyramidal weakness, foot drop, rigidity, freezing or reduced stride can look unsteady, but targeted power, reflex and movement examination reveals impaired force or initiation rather than coordination.

Functional gait disorder

Internally inconsistent balance, improvement with distraction or preserved automatic movement supports functional dysfunction, diagnosed positively while recognising that structural neurological disease may coexist.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01SUDDENAcute ataxia todayFirst stepCoordination or gait impairment began suddenly or over a few hours.

1Activate emergency neurological assessment, establish last-known-well, check glucose and observations, and identify headache, neck pain, focal signs and anticoagulant exposure.
2Arrange urgent non-contrast CT and head-and-neck vascular imaging, with MRI when required, while assessing thrombolysis or thrombectomy eligibility.
3Review alcohol, medicines, overdose, infection and electrolyte disturbance in parallel and correct immediately dangerous metabolic abnormalities.
4Admit when stroke, persistent severe gait inability, swallowing risk or diagnostic uncertainty remains; do not discharge on a normal early CT alone.

02LOCALISECerebellar or sensoryAtaxia is present without an immediately obvious acute cause.

1Examine eyes, speech, upper and lower limb coordination, reflexes, plantar responses, proprioception, Romberg, stance and gait to identify the dominant system.
2Look for neuropathy, pyramidal disease, parkinsonism, hearing loss, autonomic failure and cognition that define a broader neurological syndrome.
3Use the localisation and tempo to choose MRI, neurophysiology, nutritional, immune, malignant or genetic investigations.
4Document falls, swallowing, communication, driving and work impact and begin therapy support while diagnosis proceeds.

03PROGRESSSubacute progressionGait and coordination worsen materially over days to months.

1Reconcile every prescribed, over-the-counter and recreational exposure and assess weight loss, diarrhoea, surgery, alcohol, cancer and autoimmune symptoms.
2Obtain MRI and targeted nutritional, endocrine, inflammatory, infectious and paraneoplastic testing with neurology input.
3Treat suspected thiamine deficiency immediately rather than waiting for a concentration and correct other confirmed deficiencies safely.
4EscalationEscalate rapidly progressive disease, new cognitive change or constitutional symptoms for specialist and malignancy investigation.

04CHRONICLong-standing or familial ataxiaSymptoms evolve over years or occur in relatives across one or more generations.

1Construct a three-generation pedigree and record onset, neuropathy, eye, ear, heart, endocrine, cognitive and autonomic features.
2Exclude acquired and treatable causes before or alongside referral to a specialist ataxia and clinical genetics service.
3Use phenotype-directed repeat-expansion, mitochondrial or sequencing tests under the current NHS Genomic Test Directory.
4Provide genetic counselling, multidisciplinary rehabilitation, falls and swallowing care, and surveillance tailored to the confirmed syndrome.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Prevents progression of a time-critical, treatable thiamine-deficiency cause of ataxia and encephalopathy.

Parenteral thiamine

When Wernicke encephalopathy is possible, give high-dose intravenous thiamine immediately using the current local alcohol-treatment protocol before or alongside carbohydrate when feasible; never delay emergency glucose for hypoglycaemia.

Do not wait for a thiamine result; administer where anaphylaxis can be managed and replace magnesium when deficient because it is required for thiamine-dependent metabolism.

Treats a potentially reversible sensory, myelopathic or cerebellar contribution and prevents further neurological injury.

Cause-specific vitamin replacement

Replace confirmed vitamin B12, folate or vitamin E deficiency using the relevant NICE, BNF and specialist regimen, with route and duration determined by cause and neurological severity.

Take diagnostic blood samples first when safe but never delay emergency thiamine; avoid folate alone until B12 deficiency has been considered and monitor biochemical and clinical response.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Falls and injury

Truncal and gait instability increase fractures, head injury and fear-driven immobility, particularly when visual loss, neuropathy, orthostatic hypotension or sedating medicines add to imbalance.

Bulbar and nutritional harm

Cerebellar or multisystem disease may impair speech and swallowing, causing aspiration, dehydration, weight loss and communication difficulty that require deliberate assessment and rehabilitation.

Loss of mobility and independence

Progressive incoordination can restrict walking, driving, work and self-care; deconditioning and contracture compound disability unless physiotherapy, equipment and occupational adaptation begin early.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Repeat neurological examination and gait assessment after any acute treatment and image immediately if symptoms progress or consciousness falls.
Track falls, transfer safety and use of walking aids with physiotherapy and occupational therapy rather than relying only on finger–nose testing.
Monitor weight, swallowing, speech and respiratory or cough function when bulbar or degenerative disease is present.
Review alcohol and medicine exposure, renal and liver function and relevant drug concentrations after suspected toxicity.
For nutritional treatment, follow symptoms and the appropriate biochemical markers while investigating the cause of deficiency and risk of recurrence.
In hereditary disease, follow syndrome-specific cardiac, endocrine, hearing, visual and neurological surveillance through the specialist service.
Revisit driving and occupation when gait, eye movements, sleepiness or episodic symptoms change, applying current DVLA standards.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Romberg tests dependence on vision

Instability that appears mainly after eye closure suggests impaired proprioceptive or vestibular input; cerebellar truncal ataxia is usually evident with eyes open.

Laterality can localise

A cerebellar hemisphere commonly produces limb ataxia on the same side because cerebellar output ultimately influences ipsilateral body coordination.

Tempo outranks the list

The same broad-based gait has a radically different differential when it appeared in ten minutes, ten weeks or ten years.

Ataxia may be non-cerebellar

Severe proprioceptive loss or bilateral vestibular failure can produce striking imbalance despite structurally normal cerebellar imaging.

Drug binding can deceive

Hypoalbuminaemia can increase free phenytoin and cause toxicity even when the reported total concentration seems acceptable.

Genetics needs the right assay

Several common hereditary ataxias are repeat-expansion disorders and may be missed by an exome or generic sequencing panel.

11Common pitfallsFrequent interpretation and management errors.

01
Do not label sudden severe gait ataxia as labyrinthitis without examining eye movements, cranial nerves, limbs and the ability to stand.
02
Do not use a normal early CT to exclude cerebellar or brainstem infarction.
03
Do not equate a positive Romberg sign with cerebellar disease; it often identifies sensory or vestibular dependence.
04
Do not overlook prescribed phenytoin, lithium, benzodiazepines, alcohol or recreational toxins in an acute or subacute syndrome.
05
Do not wait for laboratory confirmation before treating possible Wernicke encephalopathy.
06
Do not order genomic sequencing without considering repeat expansions, mitochondrial testing and pre-test counselling.
07
Do not describe progressive ataxia as untreatable before excluding nutritional, immune, endocrine, toxic and structural causes.