Core rule: localise first (UMN, LMN or muscle), and any progressive leg weakness without an established cause needs urgent assessment — watchful waiting is not appropriate. New leg weakness in someone with cancer is MSCC until proven otherwise.
0Stop — call 999 now
- Sudden one-sided leg weakness with arm weakness or numbness, facial droop or dysarthria → 999 stroke pathway.
- Acute ascending bilateral weakness + areflexia, or bulbar or respiratory involvement (Guillain-Barré) → 999 admit.
- Weakness + spinal tenderness + fever with IV drug use, recent bacteraemia or immunosuppression (epidural abscess); cold, pale, pulseless, painful leg (6 P's) → 999
- While waiting: do not delay transfer for primary-care tests, imaging, LP or nerve conduction studies. No steroids in GBS.
1Triage — onset and pattern set the route
| Onset / pattern | Think → route |
|---|---|
| Sudden | Stroke, TIA, arterial occlusion → emergency |
| Hours–days | GBS, cord compression, cauda equina, abscess → emergency |
| Gradual or relapsing | MND, CIDP, MS, myasthenia, myopathy, malignancy → urgent neurology |
| Static, chronic | Old stroke, neuropathy → work-up, outpatient pathway |
2Screen — serious causes
- Back pain/sciatica + urinary retention or altered sensation, saddle anaesthesia, bilateral sciatica or progressive deficit (cauda equina) → 999 emergency spinal assessment + urgent MRI.
- Cancer + leg weakness, gait, sensory or bladder/bowel symptoms (MSCC) → Same-day MSCC coordinator now; dexamethasone 16 mg oral; whole-spine MRI ≤24 h.
- Stroke symptoms fully resolved (TIA) → ≤24 h specialist assessment.
- Myasthenia (fatigable, ptosis, diplopia) → Urgent neurology; breathing or swallowing difficulty → 999
- Proximal weakness + raised CK (myositis) → Urgent rheumatology/neurology.
- Suspected MND (mixed UMN + LMN, fasciculations) or unexplained progressive weakness → Urgent neurology; MND without delay.
3Assess
☐ Onset, distribution, sphincters, back pain, cancer ☐ Tone, power (MRC 0–5 per muscle group), reflexes, plantars, clonus ☐ Sensory level, saddle sensation; gait ☐ Leg pulses, colour, temperature ☐ Bloods by pattern: FBC, U&E, LFT, HbA1c, B12/folate, TFT; CK if proximal weakness or myalgia; ESR/CRP if inflammatory, infective or malignant
Not in primary care: routine MRI for every case; nerve conduction studies, antibodies, LP.
4Classify — only if blocks 0–2 are negative
- UMN — ↑tone, hyperreflexia, upgoing plantar, clonus; stroke, cord lesion, MS, MND. Signs may be absent early after an acute lesion.
- LMN — ↓tone, ↓reflexes, wasting, fasciculations; neuropathy, radiculopathy, GBS, MND.
- Radiculopathy — dermatomal pain + myotomal weakness; L5: foot drop, no reflex change; S1: ↓ankle jerk.
- Foot drop — peroneal palsy vs L5 root (sciatica, SLR) vs stroke (UMN): localise first.
- Muscle / NMJ — proximal, no sensory signs; inflammatory, steroid or hypothyroid myopathy; Lambert-Eaton (paraneoplastic).
- Uncertain, or progressive → urgent neurology.
5Treat today — doses: NICE/SPC, BNF, local formulary
- Sciatica, no red flags: stay active, consider physiotherapy; no gabapentinoids, other antiepileptics, oral steroids or benzodiazepines (NICE NG59).
- Neuropathic pain (not sciatica): offer a choice of amitriptyline, duloxetine, gabapentin or pregabalin (NICE CG173).
- Reversible causes: B12 deficiency → IM hydroxocobalamin; hypothyroid myopathy → levothyroxine. No high-dose steroids for myositis unless the specialist advises.
- Driving: advise not to drive while weakness could impair control; check DVLA standards for the diagnosis; document.
6Refer routinely and review
- Stable foot drop or chronic neuropathy: reversible-cause screen; neurology or spinal pathway if atypical or progressive.
- Rest pain or tissue loss → urgent vascular; claudication impairing quality of life → routine vascular.
- Once emergencies excluded: physiotherapy, orthotist (AFO), OT; falls assessment (NICE NG249).
- Review: MRC grade at each visit; re-assess and re-refer any progressive deficit.
7Never reassure by
- Continence in suspected cauda equina — incontinence is a late feature.
- A normal LP or nerve conduction study early in GBS.
- A "normal" FVC in GBS when cough is weak or bulbar signs appear.
- Absent UMN signs soon after an acute lesion.
- "Power normal" without MRC grades per muscle group.
- Watchful waiting when weakness is progressing.
8Safety-net — say it, then document it
999 “Call 999 if the weakness spreads or climbs up your body quickly, breathing or swallowing becomes difficult, you get numbness around your bottom or genitals, new trouble passing urine or loss of bladder or bowel control, sudden one-sided weakness, a drooping face or slurred speech, or a cold, pale, painful leg. If you have cancer: 999 for new leg weakness, numbness or bladder or bowel change.”
Same day: “Contact us or NHS 111 the same day if the weakness gets worse over days or you get new numbness or tingling. If you have cancer and get new back or neck pain, contact your cancer team or us the same day.”
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies; onset and pattern recorded
Saddle sensation, bladder and back asked; cancer history checked
Tone, MRC power, reflexes, plantars, sensory level recorded
Bloods by pattern sent; route matched to tempo
Driving, falls and safety-net advice documented
Summary of the full Reasoning GP leg weakness algorithm, which holds the history, examination, investigations, rehabilitation and evidence. Sources: NICE NG234 (MSCC), NG128 (stroke), NG59 (sciatica), NG42 (MND), CG173 (neuropathic pain), NG249 (falls), EAN/PNS Guillain-Barré guideline 2023, DVLA. Clinical reference — follow local pathways and check doses: NICE/SPC, BNF.