Nerve lesions

Lesion: a structural change in a body part due to injury or disease.

signs and symptoms of a nerve lesion are directly correlated to the function of the nerve

Definitions

Neurapraxia = segmental demyelinationLocal injury may distort/disrupt the myelin sheath locally, resulting in focal demyelination. => temporary conduction block

Sheath is restored locally

Wallerian degeneration Occurs distal to lesion site = loss of conduction Accompanied by corresponding muscle atrophy followed by removal by macrophages and recycling of myelin-

derived material

responses to Injury

Classification of Nerve lesions

Incomplete/completeComplete when all neurons traversing the injured segment are disrupted

Incomplete when not all neurons are disrupted, sparing of distal motor/sensory function

By SEVERITY

A system of classifying severityWith regard to axon

Sunderland classification system

First degree (Neuropraxia)

Reversible conduction block

Recover in hours to weeksNo need surgical intervention

Second degree Loss of continuity to axons No need surgical intervention

Third degree Damage to axons and surrounding structures

Recovery variable

Fourth degree Damage to axons, scarring prevents nerve regeneration

Surgery with nerve grafting needed

Fifth degree Usually in laceration/stretch injuries: nerve divided into 2

Same as above

NB: some sources include ‘sixth degree’- mixed patterns of injuryAffects management of injury

about the classification

By how they damage nerves:Those which cause anoxic anoxia

CO, cyanideThose which cause demyelination

Lead, trimethyl tin, thalliumThose which damage peripheral neurons

Usually from chronic exposure e.g. Ethanol, organophosphates (e.g. malathion, DDT)

Those which damage cell body of neuron Organic mercury, vinca alkaloids

Those which damage NMJ specifically tetrodoxin (from pufferfish), botulinum toxin (botox),

Those which cause lesions within CNS e.g. Gold thioglucose

For Neurotoxins:

methods and reflex testsDiagnosis

Recall: reflex arcSensory -> interneuron -> motor

Tests help in localisation of nerve lesions(some primitive reflexes are a sign of brain

injury in general)

Reflex tests

Name What you have to do

Positive sign What it means

Orbicularis oris/snout/nasomental

tap finger/tongue depressor on lateral corner of mouth/lips

pursing oflips

exaggerated with lesions affecting supranuclear corticopontine pathways- e.g. multi-infarct dementia, extrapyrimidal diseases e.g. Parkinson)

Suck Gently stroke lips Sucking/swallowing movements

Biting

Mouth opening and head turning to stimulus

Normal in babies, but in adults indicates sv, diffuse brain injury

Wartenberg/’thumb sign’

Forcefully flex 2nd-5th fingers

Flexion of thumb Pyramidal tract lesion

Palmomental (exaggerated/asymmetrical)

Intensely stroke ball of thumb/palm of hand with fingernail

Contraction of ipsilateral chin muscles 

If unilateral, contralateral brain lesion;also in diffuse cerebral injury

Pathological Reflexes

Name of reflex What you have to do Positive sign What it meansGrasp stroke palm finger flexion,

graspingNormal in infantsOtherwise, sign of diffuse brain injury

Gegenhalten (paratonia)

Attempted passive stretching of muscle

active and intense contraction of muscle in question – patient involuntarily resist movement

 Frontal lobe damage, neurodegenerative conditions

Grasping/groping (magnet phenomenon)

object brought near palm of conscious patient

Hand follows presented object like a magnet

Normal in infantsOtherwise, sign of diffuse brain injury

Mass reflexes of lower limbs

Forceful passive flexion of toes/forefoot (Marie-Foix handgrip)

Retraction of lower limb by flexion at knee and hip

reveals intactness of spinal reflex arc => peripheral nervous sys

reflex tests

Name What you have to do

Positive sign What it means

Babinski reflex Stroke lateral edge of foot from heel to 5th toe

Tonic extension of big toe, other toes remain/splayed

Lesion of pyramidal pathway on corresponding side

Oppenheim reflex Forcefully stroking ant. margin of tibia, proximal -> distal (painful!)

Same as Babinski  

Grasping/groping (magnet phenomenon)

object brought near palm of conscious patient

Hand follows presented object like a magnet

Normal in babies, sign of diffuse cerebral injury in adults

Gordon reflex Forcefully stroking/squeezing calf muscles

Same as Babinski  

reflex tests

Often used with EMG to differentiate nerve disorder from muscle disorder

Speed of conduction depends on degree of myelination diameter of nerve

Normal: 50-60m/s Slower could indicate problems with

myelinationFalse negative: lower body temperature => slower conduction

Nerve conduction velocity test

Procedure:Two electrode patches placed on skin over the nerve; electrodes attached

One electrode stimulates the nerve with electrical current. The other records the nerve’s

Time taken for electrical impulse to travel betweenprobes is measured.

NCV cont’d

Gold standardfor neuromusculardisorders

Procedure:Needles are inserted through skin into muscleElectrical activity is measured during rest, slight contraction and forceful contraction

Electromyogram (EMG)

To identify nerve defect more specifically Typical sites: radial, sural nerves

Nerve biopsy

Common peripheral nerve lesionsSigns and symptoms

Nerve Probable cause

Sensory loss Motor loss

Sciatic n. ● penetrating wounds,

● fractures of the pelvis

● hip dislocations

● badly-placed intramuscular injections

Below knee except medial side of leg and medial border of foot Tingling suggests nerve is not totally severed

● Weakness extending hip joint and flexing knee joint due to impaired hamstring ability

● Cannot move foot● Cannot bend knee● Foot drop (below)

Lower limbs

Nerve Probable cause

Sensory loss Motor loss

Common peroneal nerve

Commonly injured in fractures of the neck of the fibula.

LOS on skin of leg & foot anteriorly & laterally except the lateral border of the foot (sural nerve) and medial border of the foot (saphenous).

● Damaged to innervation of anterior leg muscles => weakened extension of ankle

● Innervation (superficial peroneal nerve) to lateral leg muscles damaged=>

● weakened flexion of ankle joint; inversion of foot

● Unsupported/unopposed foot exhibits foot drop and inversion (equinovarus) (below)

Lower limbs

Lower limbs

Nerve Probable cause

Sensory loss Motor loss

Femoral n.

Rarely injured unless gunshot/stab wounds

LOS over anterior and medial sides of thigh, along medial border of leg as far as big toe

Unable to flex knee as all quadriceps muscles are paralyzed

Tibial n. Rarely injured; protected by muscles

● LOS on sole of foot● Ulcers can develop

● Posterior muscles of leg paralysed => no plantar flexion

● Foot is dorsiflexed and everted => calcaneovagus (left)

 

upper limbs nerve lesions (brachial Plexus)

  Probable cause Motor loss Sensory loss Observable effect

Axillary n.

Badly adjusted crutch, downward displacemt of humerus in shoulder dislocations, humerus fracture

Paralysis of deltoid/teres minor

Lower deltoid Cannot abduct arm past 15 deg

Radial n.

Axilla lesion: triceps, anconeus, extensor m. of forearm

Post. forearm, lat. dorsum of hand, lat. 3.5 fingers

Cannot extend elbow + wrist joint, fingersWrist drop (below)

Upper limbs

NB: Radial n. lesions are also called  ’Saturday night palsy’ because people get drunk and fall asleep with their arms hanging over the backs of chairs. Also ‘Honeymoon palsy’ when one of the newlyweds sleeps on the arm of the other.

Upper limbs

left image: positive Froment’s sign

Upper limbs

Body’s response to injury

Nerves can regrow under favourable environment of the Schwann cells

In contrast, oligodendrites and astrocytes in CNS are generally inhibitory to axonal growth

can nerves recover?

Recovery depends on severity (naturally)

depends on severity

Type of injury Spont? Rate of recovery

Surgery

First degree Full Days- 3 months after injury

None

Second degree Full Regenerates: 1 in/mth

Third degree Partial Neurolysis?

Fourth degree None After surgery, 1 in/mth

Nerve repair, graft, transfer

Fifth degree None

1. Macrophage invasion mitogenic input to Schwann cell remove debris (e.g. axonal fragments)

2. Regenerating axon sprouts within hours3. Axon contacts the Schwann cell basal laminae on

one side and the Schwann cell membrane on the other

Schwann cell basal lamina provides promoters of axonal outgrowth (e.g. laminin, fibronectin)

Schwann cell directs regenerating axon back to its target using endoneurial tube

But can result in neuroma formation4. BUT loss of cell body = irreversible

e.g. polio, motor neurone disease No regeneration is possible

After an injury

Limited because:neurons are postmitotic in the mature CNSneurons are localised to certain sitesglial cells in CNS are inhibitory to axonal outgrowth

Regeneration in CNS

of nerve lesionsTreatment

Surgical NonsurgicalIndications:•Injury/continuity defect in nerve which cannot regain normal function without surgical intervention•Loss of normal neural function which cannot be corrected non-surgically•Distressing subjective symptoms

Indications:•Evident improvement indicating electrical regeneration•Mild, tolerable subjective symptoms

• Effects last longer • Short-term

Categories of treatment

of nerve lesionssurgical Treatment

= joining up of the ends of the nerves using sutures

Best when nerve has been cut sharplyBUT nerve elasticity causes retraction of

segmentscauses tension

can lead to scarring, ischemia

Nerve repair

Requires a donor nerveAverage size 2-5cm

Cable grafts used if greater than 2-3cm->Most common:

Sural n.Great auricular n.

Decided by Ease of harvestingMinimising resulting loss of function

Because once you take out the donor nerve, the dermatomes it innervates will have no sensation etc.

Nerve graft

To consider:Diameter of donor and host nerves

Should match!! But can combine 2 strands => bigger diameter (“cable

graft”)Length of graftNumber of fasciclesCross-sectional shape and area

Nerves can be round or flatPatient preference!

Harvesting donor nerve => loss of sensation, patients might prefer that the loss of sensation be somewhere specific.

When choosing donor nerves

VascularitySchwann cells survive when the graft is revascularised quickly

Time since injuryAvoids problems like Wallerian degeneration, etc.

Extent of injury/length of graft required(for peripheral nerves) Tension on prepared

nerveThe limb must be kept in a relaxed position

What affects recovery

Other tissues can be used to graft nerves too!

Most common: veinsGenerally good results in studiesEasy to find good size match for nerves

BUT:poor resistance to kinking and collapse

Unsuitable for longer grafts

Nerve grafting: alternatives

of nerve lesionsnonsurgical Treatment

= removal of scar tissueWorks best when

nerve is entrapped, not cutnerve is not transected, electrical impulses still can flow

Requires skill and cautionMight damage surrounding, functional nerves

Neurolysis

MedicationLifestyle changes

e.g. for carpal tunnel syndrome, patients can be taught to take frequent breaks during repetitive tasks

NSAIDS relieve pain

Nonsurgical treatment

Transcutaneous nerve stimulation (left)using gating mechanism

Physical therapyRadiofrequency techniques

‘cooking’ the nerve!

Nonsurgical treatment

Regional nerve-blocking procedures using local anestheticsLocal anesthetic at nerveAt neuroma

= mass of nerve fibres and Schwann cells formed after injury

Neurolysis at peripheral nerves Usually for terminal patients Phenol/ethanol injected directly to nerves supplying body

part in pain Effect lasts 6-8 weeks

nonsurgical treatment

Sources and biblio

http://www.instantanatomy.net/arm/nerves/medianwrist.htmlhttp://www.aic.cuhk.edu.hk/web8/peripheral_nerve_lesions.htmhttp://www.ncbi.nlm.nih.gov/pubmed/8832668http://www.rsdsa.org/glial_workshop/glialpdf/James_Campbell/NerveLesionsPain.pdfhttp://emedicine.medscape.com/article/1172408-overviewhttp://www.hopkinsmedicine.org/neurology_neurosurgery/specialty_areas/peripheral_nerve_surgery/conditions/nerve_injury.html

NCV and EMG: http://www.nlm.nih.gov/medlineplus/ency/article/003927.htm - NCVhttp://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=92&ContentID=P07657http://www.hopkinsmedicine.org/healthlibrary/test_procedures/neurological/electromyography_emg_92,P07656/ - about EMGhttp://www.neneuro.com/nn_12_use_of_emg.html - Use of EMG in nerve/muscle disord

sources

Cell response to injury:http://faculty.swosu.edu/scott.long/txcl/cnstox.htm - CNS toxinshttp://www.jneuroinflammation.com/content/8/1/109Surgical Management of Pain edited by Kim Burchiel

Treatment of nerve lesions:http://www.medscape.com/viewarticle/423216_6http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1201001/http://surgerydept.wustl.edu/Surgery_M.aspx?id=2936&menu_id=284http://cal.vet.upenn.edu/projects/saortho/chapter_65/65mast.htmhttp://www.painclinic.org/treatment-peripheralnerveblocks.htm - Nerve blockshttp://emedicine.medscape.com/article/1298684-treatment

Clinical:http://www.dartmouth.edu/~dons/index.html

sources

PICTURES:http://images.rheumatology.org/image_dir/album75674/md_99-12-0031.tif.jpghttp://1.bp.blogspot.com/-WhtUSzuIB54/ThhNNr7QF4I/AAAAAAAACu0/6bJ_wG8OLfk/s1600/Radial+nerve-wrist+drop.jpghttp://www.bailey-law.com/docs/acute-nerve-injuries.htmhttp://www.taringa.net/posts/imagenes/15519439/Sabia-usted-que____-_Propio_-_Curiosidades_.html

INTERESTING READINGS:http://ntp.neuroscience.wisc.edu/neuro670/reqreading/RegeneratingTheNervousSystem.pdf

Picture sources