Weakness: Red Flags & Emergency Signs
Sudden unilateral weakness of the face, arm, or leg is a stroke until proven otherwise and the window for thrombolysis is only 4.5 hours — every minute of delay costs neurones.
If you have this symptom right now
Call 999 (UK) / 112 (EU) / 911 (US) immediately if any emergency warning signs are present. Do not drive yourself. Do not wait to see if it improves.
🚨 Call 999 / 112 Immediately
- ⚠Sudden one-sided weakness of face, arm, or leg — stroke (FAST), call 999 immediately
- ⚠Weakness spreading upward from legs over hours to days — Guillain-Barré syndrome (respiratory arrest risk)
- ⚠Sudden bilateral leg weakness with back pain and bladder/bowel dysfunction — cauda equina syndrome (surgical emergency)
- ⚠Weakness with confusion and fever — sepsis-associated encephalopathy
⚡ See a Doctor Today
- •Weakness that resolved within hours (possible TIA) — high stroke risk within 48 hours
- •Progressive weakness over weeks (motor neurone disease, spinal cord compression, malignancy)
- •Weakness worse at end of day (myasthenia gravis — ocular/bulbar involvement = airway risk)
High-Risk Combinations
When weakness occurs together with any of these symptoms, urgency increases significantly:
Conditions to Rule Out Urgently
FAST + 999; CT brain; thrombolysis window 4.5 hours
ABCD2 score; same-day specialist review
Ascending paralysis; LP (albumino-cytological dissociation); IVIG
MRI spine <4 hours; emergency surgical decompression
Focal weakness resolves with glucose correction
MRI brain/spine; CSF oligoclonal bands; neurology referral
Condition Authority Pages
Differential diagnosis analyses:
When to Call Emergency Services
- →Any sudden one-sided weakness — FAST test positive = 999 now
- →Weakness spreading rapidly up both legs
- →Weakness with bladder or bowel dysfunction and back pain