Synopsis
Localise common focal nerve lesions from motor, sensory and provoking patterns, distinguish them from root and plexus disease, and select urgent decompression, conservative care, neurophysiology or surgery appropriately.
- Localise before naming: identify every weak movement, reflex change and sensory territory, then compare muscles supplied by the same root through different peripheral nerves.
- Carpal tunnel syndrome causes nocturnal paraesthesia in thumb, index, middle and radial ring fingers with later thenar weakness; sensation over the thenar eminence is often spared because the palmar cutaneous branch travels outside the tunnel.
- Anterior interosseous neuropathy is motor only, weakening flexor pollicis longus and index flexor digitorum profundus so the patient cannot make a round thumb-index OK sign.
- Ulnar neuropathy at the elbow causes small-finger and ulnar-ring sensory symptoms with weak finger abduction, adduction and pinch; sustained elbow flexion or leaning commonly aggravates it.
- A lesion in Guyon's canal can spare dorsal ulnar hand sensation because the dorsal cutaneous branch arises proximal to the wrist, helping distinguish wrist from elbow localisation.
- Radial neuropathy at the spiral groove causes wrist and finger drop with triceps preserved, while posterior interosseous neuropathy weakens finger and thumb extension without cutaneous sensory loss.
- Common-peroneal neuropathy at the fibular neck weakens dorsiflexion and eversion with dorsal-foot sensory change; ankle inversion is relatively preserved, unlike many L5 radiculopathies.
- Provocative tests such as Phalen, Tinel and elbow flexion modestly shift probability but cannot diagnose entrapment in isolation or substitute for a neurological examination.
- Nerve-conduction studies localise demyelination or axonal loss and grade severity, while ultrasound or MRI identifies swelling, ganglion, tumour, anomalous muscle or compressive anatomy.
- Remove pressure and improve mechanics early, use a night wrist splint for carpal tunnel or an ankle-foot orthosis for foot drop, and refer severe, progressive or denervating lesions for timely surgical review.
Key red flags
Deficit after fracture, dislocation, deep laceration, tourniquet or expanding painful swelling requires immediate orthopaedic, plastic or vascular assessment.
Investigation priorities
Distinguish named nerve, branch, root and plexus lesions before testing.
Management branches
A patient presents with focal hand weakness, wrist drop or foot drop.
- Establish onset, pressure, posture, injury, weight loss, surgery, pregnancy, diabetes and neck or back pain, noting progression and any sphincter or systemic symptoms.
- Test each affected movement, reflex and autonomous sensory zone, then test same-root muscles supplied by other nerves to distinguish mononeuropathy from radiculopathy.
- Escalate acute traumatic, vascular, compartment, cauda-equina or rapidly progressive patterns immediately before arranging routine electrophysiology.
Key medicines
Local corticosteroid for carpal tunnelA trained clinician uses the locally approved corticosteroid and dose, commonly with local anaesthetic, after confirming anatomy, consent and contraindications.Avoid intraneural injection; discuss transient pain, skin change, tendon or nerve injury, glucose elevation and variable duration, and do not use repeated injection to postpone necessary decompression.
ParacetamolUse the current BNF adult oral regimen for short-term associated musculoskeletal pain, reducing the maximum for low body weight or liver risk.Check combination products and avoid presenting analgesia as definitive care when weakness, denervation or a structural lesion requires intervention.