Specific neurological symptoms/signs in low back pain
These are the features that make imaging/referral more justifiable because they suggest nerve root, cauda equina, or spinal cord/central canal involvement, rather than simple mechanical low back pain.
1. Radicular neurological symptoms
Pain pattern
- Leg pain worse than back pain
- Pain radiating below the knee
- Sharp, shooting, electric, burning pain
- Dermatomal distribution:
- anterior thigh/medial shin → L3/L4
- lateral leg/dorsum foot/big toe → L5
- posterior calf/lateral foot/sole → S1
Sensory symptoms
- Numbness
- Tingling
- Pins and needles
- Burning dysaesthesia
- Altered sensation in a dermatomal pattern.
Motor symptoms
- Subjective weakness
- Foot drop
- Tripping
- Difficulty climbing stairs
- Difficulty rising from chair
- Difficulty heel-walking
- Difficulty toe-walking
- Knee buckling.
Reflex symptoms/signs
- Reduced knee jerk → usually L3/L4
- Reduced ankle jerk → usually S1.
2. Objective neurological signs on examination
These are stronger than symptoms alone.
| Nerve root | Pain/sensory distribution | Motor weakness | Reflex |
|---|---|---|---|
| L2/L3 | groin/anterior thigh | hip flexion | usually none |
| L3/L4 | anterior thigh/medial shin | knee extension | reduced knee jerk |
| L5 | lateral leg/dorsum foot/big toe | ankle dorsiflexion, great toe extension | no reliable reflex |
| S1 | posterior calf/lateral foot/sole | plantarflexion | reduced ankle jerk |
Examination findings that matter
- Positive straight leg raise with radicular pain
- Positive slump test
- Dermatomal sensory loss
- Myotomal weakness
- Reflex asymmetry
- Gait abnormality
- Unable to heel-walk → possible L4/L5 weakness
- Unable to toe-walk → possible S1 weakness.
3. Severe/progressive neurological features
These are higher-risk and should prompt urgent imaging/specialist/ED assessment depending severity.
Concerning motor features
- Progressive weakness
- New foot drop
- Bilateral leg weakness
- Multi-level motor deficits
- Rapidly worsening walking capacity
- Falls due to leg weakness
- Inability to heel/toe walk compared with baseline.
Concerning sensory features
- Progressive numbness
- Bilateral sensory symptoms
- Numbness spreading across multiple dermatomes
- Saddle or perineal sensory change.
4. Cauda equina symptoms — emergency
These are the key “do not miss” neurological symptoms.
Bladder symptoms
- New urinary retention
- Difficulty starting urination
- Reduced urinary sensation
- Loss of urge to void
- Overflow incontinence
- New urinary incontinence.
Bowel symptoms
- New faecal incontinence
- Loss of bowel sensation
- Reduced anal sensation.
Saddle/perineal symptoms
- Numbness around:
- anus
- perineum
- genitals
- inner thighs
- Altered wiping sensation after toileting.
Sexual dysfunction
- New erectile dysfunction
- New loss of genital sensation
- New sexual dysfunction associated with back/leg symptoms.
Bilateral neurological symptoms
- Bilateral sciatica
- Bilateral leg numbness/weakness
- Severe bilateral radicular pain.
Cauda equina syndrome requires urgent ED referral and urgent MRI, not routine outpatient imaging.
5. Neurogenic claudication symptoms
Suggests lumbar spinal canal stenosis rather than simple acute strain.
Typical symptoms
- Bilateral or unilateral leg pain/heaviness/numbness with walking or standing
- Symptoms improve with:
- sitting
- bending forward
- leaning on trolley/walker
- Reduced walking distance
- “Shopping trolley sign”
- May have buttock/thigh/calf symptoms.
This is usually less emergent than cauda equina unless there is progressive neurological deficit, but it supports imaging if persistent/function-limiting.
6. Symptoms that are less specific
These alone do not strongly prove neurological compression:
- back pain only
- buttock pain only
- vague leg aching
- intermittent non-dermatomal tingling
- pain without weakness/numbness/reflex change
- generalised heaviness without objective signs.
They may still be clinically important, but they are weaker indications for early MRI unless persistent, severe, progressive, or functionally disabling.