Core rule: sudden-onset new ataxia is posterior-circulation stroke until excluded (FAST may be negative), and confusion, ophthalmoplegia or ataxia in an at-risk patient is Wernicke's — the full triad is not required.
0Stop — call 999 now
- Sudden-onset ataxia with ↓GCS, severe or occipital headache, vomiting, or a focal deficit (dysarthria, diplopia, dysphagia, weakness, sensory loss, visual symptoms, new deafness) → 999 stroke pathway.
- Acute vestibular syndrome with abnormal HINTS by a trained examiner (normal head impulse, direction-changing nystagmus, skew) → 999; no trained examiner → stroke pathway immediately.
- Fever + ataxia + meningism; unstable suspected Wernicke's; lithium toxicity with collapse or severe neurological features → 999
- While waiting: ABCDE, capillary glucose and treat hypoglycaemia now; do not delay transfer for bloods or outpatient MRI.
1Triage — tempo of onset decides the route
| Onset | Think → route |
|---|---|
| Minutes–hours | Stroke, drug toxicity → emergency |
| Hours–days | Wernicke's, intoxication, demyelination, cerebellitis (children) → emergency/same-day |
| Weeks | Tumour, paraneoplastic, B12/thiamine, nitrous oxide → urgent neurology |
| Months–years | Hereditary, MS, alcohol, hypothyroidism → bloods, then neurology |
2Screen — serious causes
- Wernicke's (alcohol misuse, hyperemesis, malnutrition) → Emergency transfer + parenteral thiamine first if available.
- Child, sudden-onset or rapidly progressive ataxia → Same-day acute paediatrics; 999 if ↓GCS, persistent vomiting, severe headache, meningism, focal deficit, ingestion or unable to walk.
- Headache worse on waking, vomiting, papilloedema → Same-day imaging.
- Phenytoin, carbamazepine or lithium with nystagmus, slurred speech, drowsiness → Same-day review + urgent levels; emergency assessment if significant toxicity.
- Adult, rapidly progressive over days–weeks → Urgent suspected cancer pathway (NG127 1.4.2); same-day if headache, vomiting, papilloedema or focal deficit.
- Nitrous oxide + paraesthesia, numbness, weakness or urinary symptoms → Urgent neurology; treat without delay.
3Assess
☐ Glucose, BP, conscious level, temperature ☐ Finger-nose, heel-shin, dysdiadochokinesia, nystagmus, speech ☐ Romberg only if safe standing eyes open; gait with assistance ☐ Eye movements, fundi, hearing ☐ Tone, power, reflexes, proprioception, vibration ☐ Alcohol, drug and nitrous oxide history ☐ Chronic: FBC, U&E, LFT, glucose/HbA1c, B12/folate, TFT, calcium; consider coeliac serology; drug levels
Not in primary care: MRI, EEG or genetics without specialist input.
4Classify — only if blocks 0–2 are negative
- Cerebellar — wide-based gait, intention tremor, nystagmus, past-pointing; alcohol, MS, tumour, hereditary, paraneoplastic.
- Sensory — Romberg positive, stamping gait, falls in the dark; B12 (incl. nitrous oxide), neuropathy, dorsal columns.
- Vestibular — veers, vertigo, no limb incoordination; severe truncal ataxia or new deafness → think central.
- Reversible — alcohol, antiepileptic or lithium toxicity, thiamine or B12 deficiency, hypothyroidism → treat.
- Uncertain, or progressive despite normal bloods → neurology.
5Treat today — doses: NICE/SPC, BNF, local formulary
- Neurological B12 deficiency: IM hydroxocobalamin loading, B12 before folate; nitrous oxide → parenteral B12 + urgent specialist advice.
- Harmful or dependent drinker at risk: offer prophylactic oral thiamine (NICE CG100) + alcohol support.
- Drug toxicity: agreed plan with specialist/acute advice; never stop antiepileptics or lithium abruptly without one.
- Driving: advise not to drive if symptoms could impair safe control; check DVLA standards, notify where required; document.
6Refer routinely and review
- Gradually progressive unsteady gait: neurology (NG127), alongside the reversible-cause screen; hereditary → genetics.
- Rehabilitation: physiotherapy, OT, falls prevention; SALT for dysarthria. Choking, wet voice, chest infections → urgent swallow assessment.
- After treating the cause: reassess; persisting or progressive → neurology. Recheck levels after dose changes.
7Never reassure by
- A negative FAST — posterior-circulation stroke can show isolated ataxia.
- An incomplete Wernicke triad.
- A normal serum B12 in a nitrous oxide user.
- A normal blood screen when ataxia is progressive.
- "Labyrinthitis" when acute hearing loss comes with vertigo.
- A "negative" HINTS outside acute vestibular syndrome or by an untrained examiner.
8Safety-net — say it, then document it
999 “Call 999 if the unsteadiness suddenly gets worse, or you get a new headache, vomiting, drowsiness, confusion, double vision, weakness, numbness, trouble swallowing or breathing, or a fever with a stiff neck or dislike of light.”
Same day: “Contact us the same day if the unsteadiness worsens over days, or you get new nerve symptoms, slurred speech or drowsiness on your medicines, or a fever with new symptoms. Take care to avoid falls.”
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies; tempo recorded
Glucose checked; cerebellar, sensory, vestibular signs recorded
Alcohol, drug and nitrous oxide history; levels if relevant
Reversible-cause bloods sent; route matched to tempo
Falls, driving and safety-net advice documented
Summary of the full Reasoning GP ataxia algorithm, which holds the history, examination, investigations, rehabilitation and evidence. Sources: NICE NG127, NG128 (stroke), CG100 (thiamine), NG20 (coeliac), ABN nitrous oxide guideline 2024, National Clinical Guideline for Stroke 2023, DVLA. Clinical reference — follow local pathways and check doses: NICE/SPC, BNF.