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Peripheral Mononeuropathies

Brachial plexus (C5-T1) Palsy

Presents with pain, paraesthesia and weakness of affected arm.


Causes - Trauma, radiotherapy, prolonged wearing of a heavy rucksack, cervical rib fracture, thoracic outlet compression


Erb’s Palsy occurs when there's damage to the upper trunk of the brachial plexus (C5, C6), causing weakness of its innervating muscles. It classically presents with the arm in a "waiters tip" position:

  • Arm adducted – weak shoulder abductors

  • Elbow extended – weak flexors

  • Forearm pronated – weak supinators

  • Wrist flexed – weak extensors

Radial Nerve (C5-T1) Palsy

Main function of this nerve is to open the fist.

Causes include:

  • Saturday night palsy – Patient sleeping with arm over back of chair - Alcohol is a major factor here

  • Crutches

  • Handcuffs

  • Humeral shaft fracture

Presents with Wrist drop, and complete weakness of arm extensors.

  • If the palsy is only of its posterior interosseous branch, there'll be weakness of FINGER EXTENSION ONLY w/o wrist drop


Median Nerve (C6-T1) Palsy

This nerve innervates the muscles of precision grip. Risk factors are genetic tendency (biggest factor), pregnancy (more fluid puts pressure on nerves in hand and wrist), trauma, and obesity.


Presentation - Depends on the location of the lesion:

  • Carpal Tunnel syndrome (Wrist) - Sensory loss of radial 3.5 hand, Weakness of thumb abduction (abductor pollicis brevis)

  • Anterior Interosseous syndrome - Weakness of 1st and 2nd finger pinch (distal phalanx)

  • Proximal – may show combined defects


Symptoms are usually exacerbated by sleep, repetitive hand movements or sustained posture, and relieved by shaking the hand or hanging it over the edge of a bed.


Examination - Tinel’s and Phalen’s tests


Management - Splinting, Steroid injections, Decompression surgery

Ulnar Nerve (C7-T1) Palsy

This nerve innervates the intrinsice muscles of the hand. Lesions tend to be at either the elbow (90%) or wrist (10%).


Presentation:

  • Ulnar Claw - weakness of 4th and 5th fingers

  • Sensory loss over 5th and half of 4th fingers

  • Wasting and Dorsal guttering on ulnar side

Lateral cutaneous nerve of the thigh (L2-L3) Palsy – Meralgia Paraesthetica

Caused by nerve entrapment under the inguinal ligament.


Presents with anterolateral shooting, burning thigh pain.

Sciatic nerve (L4-S3) Palsy

Presents with:

  • Weakness of hamstring and all muscle below knee (Foot drop)

  • Sensory loss below knee laterally


Common peroneal nerve (L4-S1) Palsy

Causes - Trauma, Sitting cross-legged for long periods


Presentation:

  • Foot drop

  • Weak foot EVERSION

  • Sensory loss over dorsal foot

An important differential to consider her is an L4/5 radiculopathy, which would also present with foot drop, but the patient would instead have weak foot INVERSION and back pain.


Tibial nerve (L4-S3) Palsy

Presentation:

  • Weak plantarflexion, foot inversion, toe flexion

  • Sensory loss over sole of foot

Mononeuritis multiplex

This is the involvement of 2+ peripheral nerves, and is rapidly-evolving.


Its most common cause is Vasculitis, but other causes include DM, RA, SLE, Amyloidosis, Sarcoidosis, Leprosy.



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