Reasoning GP · Algorithm · 1-page summary
Foot drop in adults
For: adults with new or persistent weakness of ankle dorsiflexion, in primary care. Not for: sciatica without weakness (use the sciatica algorithm); known cancer with spinal symptoms also follows the MSCC protocol.
Core rule: foot drop is a sign, not a diagnosis. Localise the lesion with a full neurological examination before blaming the peroneal nerve. Sudden onset, bilateral weakness, upper motor neurone (UMN) signs or sphincter change are never a simple nerve palsy.
0Stop — emergency now — before any history
- Sudden-onset foot drop or limb weakness, even in one limb and even if FAST-negative, or with arm, face, speech or visual symptoms → 999 / stroke pathway. Exclude hypoglycaemia.
- Cauda equina — any one: new urinary retention or altered urinary sensation, urinary or faecal incontinence, saddle numbness, sexual dysfunction, bilateral sciatica or progressive leg weakness → Immediate emergency assessment via the local spinal pathway; MRI is arranged there.
- New, severe or rapidly progressive bilateral weakness, bulbar or respiratory symptoms, reduced consciousness or suspected sepsis → Emergency hospital
- Known cancer + any leg weakness, other neurology, or severe, progressive or nocturnal spinal pain → MSCC coordinator now. With neurological signs: whole-spine MRI within 24 h; dexamethasone 16 mg orally per the MSCC pathway (discuss first if lymphoma possible).
1Triage by onset and course — once block 0 is clear
| Onset / course | Action |
|---|---|
| Sudden / rapid | Block 0: 999 or Same-day emergency |
| Days to weeks | Progressive, MRC ≤3, or no obvious compressive cause → Urgent neurology ≤2 weeks |
| Static, clear cause | Leg crossing, squatting, cast, weight loss: remove the cause; review MRC grades. |
2Screen — one row is enough
- UMN signs (spasticity, clonus, extensor plantar, sensory level) + progression, gait or sphincter symptoms → Same-day emergency. Stable → Urgent specialist
- Fever + back pain + neurological deficit (spinal infection) → Same-day hospital
- Gradual + opposite arm or face weakness, cortical signs → Urgent specialist + brain imaging.
- MND: painless progressive weakness, wasting, fasciculations, mixed UMN + LMN signs → Neurology without delay; say "MND".
- Weight loss + asymmetric leg weakness (malignant plexopathy until excluded), or mononeuritis multiplex → Urgent specialist
3Assess — once blocks 0–2 are answered
☐ MRC grades both sides, incl. eversion and inversion ☐ Reflexes, tone, plantars, clonus ☐ Sensory map; bladder, bowel, saddle ☐ Gait, falls risk ☐ Fibular head, SLR; arms if central
Targeted bloods: HbA1c, FBC, CRP/ESR, B12/folate, TSH, U&E, LFTs. Not: tumour markers or PSA for foot drop; lumbar MRI alone with UMN signs (needs whole spine). NCS/EMG never delays emergency imaging.
4Classify — only if the screen is negative
- Common peroneal nerve at fibular head (most common) — weak dorsiflexion + eversion, inversion preserved, no back pain → remove the compression.
- L5 radiculopathy — inversion also weak, back pain, positive SLR → sciatica care; MRI only if it changes management.
- Lumbosacral plexopathy — several roots; severe leg pain before weakness (diabetic amyotrophy) → specialist.
- Central (cord or brain) or MND → blocks 0–2.
- Uncertain — no single muscle test is definitive. Say so; refer to neurology for neurophysiology.
5Treat today — doses: NICE/SPC, BNF, local formulary
- Falls: assess now. Poor foot clearance → orthotics (AFO) without waiting for results; daily skin checks if sensory loss.
- Peroneal compression: stop leg crossing and squatting, pad the fibular head, bivalve a tight cast. No fixed recovery promise.
- Radicular pain: stay active; consider an NSAID after risk check. Do not offer gabapentinoids, oral steroids or benzodiazepines for sciatica. Peroneal neuropathic pain (not sciatica): CG173 choice of amitriptyline, duloxetine, gabapentin or pregabalin.
- Driving: not if vehicle control is unsafe, whichever side; duty to tell DVLA if it is likely to affect safe driving.
6Refer routinely
- Physiotherapy (gait, falls); OT home assessment.
- UMN foot drop (stroke, MS) → stroke pathway / rehabilitation for AFO or FES (NG236, HTG178).
- Sciatica: progressive deficit → spinal review, no fixed wait.
- Peroneal palsy not improving once the cause is removed → neurology.
7Never reassure by
- A negative FAST test in sudden limb weakness.
- A "peroneal palsy" label without testing inversion, reflexes and plantars.
- A normal lumbar MRI when there are UMN signs — the lesion may be cervical or thoracic.
- Painless weakness — MND is typically painless.
- A Tinel's sign at the fibular head — neither necessary nor diagnostic.
- "Some weakness" with no MRC grade — you cannot tell recovery from decline.
8Safety-net — say it, then document it
999 “Sudden weakness, or new weakness of the arm or face, slurred speech or vision problems — call 999.” Emergency now “Go to A&E straight away if you can't pass urine or it feels different, lose bladder or bowel control, feel numb around your back passage or genitals, the other leg becomes weak, the weakness worsens quickly, you have cancer with new back pain, or you have trouble swallowing or are breathless at rest or lying flat.”
GP same week “A fall, a sore under the brace, new tingling in the other leg or uncontrolled pain — see us this week.” Review with MRC grades, sooner if severe or progressive; L4/L5 with MRC still ≤3 at 3 months → urgent neurosurgery referral.
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies; bladder, bowel, saddle asked
Full neuro exam with MRC grades, reflexes, plantars
Lesion localised, or uncertainty stated and referred
Falls, AFO and driving advice recorded
Safety-net given; review date set
Summary of the full Reasoning GP foot drop algorithm, which holds the localisation, examination, cause-specific treatment and evidence. Sources: NICE NG127, NG234, NG128, NG42, NG59 (updated July 2026), CG173, NG236, HTG178; local gabapentinoid guidance; DVLA and GMC fitness-to-drive guidance. Clinical reference — follow local stroke, spinal and MSCC pathways and check doses: NICE/SPC, BNF.