Peripheral Nerve Injuries

PATHOLOGY

Nerves can be injured by ischaemia ,compression, traction, laceration or burning. Damage varies in severity from transient and quickly recoverable loss of function to complete interruption and degeneration.

There may be a mixture of types of damage in the various fascicles of a single nerve trunk.

Nerve injury and repair

(a) Normal axon and target organ (striated muscle). (b) Following nerve injury the distal part of the axon disintegrates and the myelin sheath breaks up. The nerve cell nucleus becomes eccentric and Nissl bodies are sparse. (c) New axonal tendrills grow into the mass of proliferating Schwann cells. One of the tendrill will find its way into the old endoneurial tube and (d) the axon will slowly regenerate.

Nerve injury and repair

Introduction Anatomy

Peripheral nerves are made up of axon endoneurium Connective tissue perineurium epineurium Nerve trunks myelinated fibre unmyelinated fibreMyelin, protein-lipid complex function, insulating layer increase conduction rate

Myelinated nerve are separated by nodes of Ranvier, at these points , the axons are bare.

Impulses jump from one node to the next ---

Saltatory Conduction Conduction in unmyelinated nerve is slower and

dependent on the diameter of axon.

Schwann cells

axon

Ranvier node

Pathological processes

Cause: damage of cell body,axon, myelin sheath, connective tissue, blood supply

Three basic processes

1. Wallerian degeneration

2. Axon degeneration

3. Demyelination

Nerve injuries types

Neurapraxia

Axonotmesis Neurotmesis

Neurapraxia

Seddon(1942) coined the term 'neurapraxia' to describe a reversible physiological nerve conduction block in which there is loss of some types of sensation and'muscle power followed by spontaneous recovery after a few days or weeks. It is due to mechanical pressure causing segmental demyelination and is seen typically in 'crutch palsy', pres- sure paralysis in states of drunkenness ('Saturday night palsy') and the milder types of tourniquet palsy.

Neurotmesis

In Seddon's original classification, neurotmesis meant division of the nerve trunk, such as may occur in an open wound. It is now recognized that severe degrees of damage may be inflicted without actually dividing the nerve. If the injury is more severe, whether the nerve is in continuity or not, recovery will not occur. As in axonotmesis, there is rapid wallerian degeneration, but here the endoneurial tubes are destroyed over a variable segment and scarring thwarts

CLASSIFICATION OF NERVE INJURIES

Seddon's description of the three different types of nerve injury (neurapraxia, axonotmesis and neurotmesis) served as a useful classification for many years. Increasingly, however, it has been recognized that many cases fall into an area somewhere between axonotmesis and neurotmesis. Therefore, following Sunderland, a more practical classification is offered here.

First degree injury This embraces transient ischaemia and neurapraxia, the effects of which are reversible.

CLASSIFICATION OF NERVE INJURIESSecond degree injury This corresponds to Seddon's axonotmesis. Axonal degeneration takes place but, because the endoneurium is preserved, regeneration can, lead to complete, or near complete, recovery without the need for intervention.

Third degree injury This is worse than axonotmesis. The endoneurium is disrupted but the perineurial sheaths are intact and internal damage is limited. The chances of the axons reaching their targets are good, but fibro- sis and crossed connections will limit recovery.

1.Wallerian degeneration

Distal axon degeneration, following section or severe injury, with degeneration of the myelin. The process occurs within 7-10 days of injury and this portion of the nerve is inexcitable electrically.

2. axon degeneration

Distal degenerated nerve is inexcitable electrically.

Regeneration can occur since the basement membrane of the Schwann cell survives and act as a skeleton along which tha axon regrows up to a rate of about 1mm per day.

3. Demyelination

Segmental destruction of the myelin sheath occurs without axonal damage. The primary lesion affects the Schwann cell and causes marked slowing of conduction or conduction block.

Local demyelination is caused by inflammation, eg: Guillain-Barre syndrome.

Symptoms of PNS

Sensory symptoms Motor symptoms

Negative symptoms:

Large myelinated fibre disease (loss of touch and joint-position sense, proprioception) leading to:

Difficulty discriminating textures feet and hands feeling like “cotton wool” Gait unsteady through loss of position sense

Small unmyelinated fibre disease (loss of pain and temperature appreciation), causes

Painless burns and trauma Damage to joints (Charcot’s joint ), resulting in painless

deformity

Positive symptoms

Large myelinated fibre disease cause paraesthesia ( pins and needles) .

Small unmyelinated fibre disease produce painful positive symptoms:

Burning sensation Dysaesthesia—pain on gentle touch Hyperalgesia—lowered threshold to pain Hyperpathia—pain threshold is elevated but pain is

excessively felt Lightening pains—sudden, very severe, shooting pains,

which usually suggest a diagnosis of tabes dorsalis (late syphilis)

Motor symptoms:

Weakness—the main presenting feature, usually distal (e.g. difficulty clearing the kerb when walking or weak hands)

Sometimes can be proximal (e.g. difficulty climbing stairs or combing hair)

Cramps and twitching of muscles (fasciculation) more commonly due to neuronopathies (diseases affecting the anterior horn cell, eg. motor neuron disease)

Signs of Peripheral Neuropathy

Sensory examination:

Large myelinated sensory fibres include: Light touch two-point discrimination Vibration sense Joint-Position sense

Small unmyelinated and thinly myelinated sensory fibres include:

Temperature perception Pain perceptionPolyneuropathy: “glove-and-stocking”

distribution of sensory loss.Joint-position sense is lost, gait is abnormal

(sensory ataxia), Romberg’s test (+). It can be compensated for by vision, therefore the stance becomes unsteady when the eyes are closed.

Motor examination:

Classical features of a lower motor neuron abnormality include:

Distal Wasting of muscles, can occur with generalized weight loss, but weakness is rare.

Weakness of muscles Depressed or absent tendon reflex Fasciculation

Investigation of peripheral neuropathy

Blood tests: FBC, ESR, CRP, urea and electrolytes, liver function tests, VitB12 、 protein electrophoresis.

Nerve conduction studies -differentiate axonal degeneration (reduced amplitude) from demyelination (reduced conduction velocity). Characterize whether sensory motor fibres; localize the sites of abnormality.

Electromyography (EMG): discern complete of partial denervation /reinnervation; localization depending on the distribution of muscles affected.

Nerve biopsy:

sural nerve is the one most commonly biopsied provided that its conduction is abnormal.

Cerebrospinal fluid (CSF) examination: Guillain-Barre syndrome or chronic inflammatory demyelinating polyradiculoneuropathy: protein content is usually raised.

Trigeminal Neuralgia

Introduction A severe paroxysmal facial pain syndrome Pain is confined mainly to the area supplied by the

second and third divisions of trigeminal nerve. Characteristically, lightninglike momentary jabs of

excruciating pain occur and spontaneously abate. Develops in middle to later life Uncertain cause.Microvascular compression is the

cause in some cases.

Clinical features

—Most patients are over 40 years old—Female more than male, 3:2 or 2:1 —Pain area: in a maxillary or mandible distribution , most

are unilateral —Pain quality: severe paroxysmal lightninglike jabs of

excruciating pain and stop spontaneously. Pain-free Interval may last for minutes to weeks.

—Trigger zones: cheek, nose or mouth by touch, cold, wind, drinking, talking or chewing can precipitate the pain.

—Long-term relapse and remission course —Physical examination: no abnormal signs.

Treatment

Carbamazepine 600-800 mg/d orally is preferred. Side effects include drowsiness, unsteadiness of gait, nausea, vomiting.

Phenytoin 200-400mg/d orally is the second choice, can combine with carbamazepine.

Intravenous administration of phenytoin 250mg will abort an acute attack.

Lamotrigine 400mg/d or baclofen 10mg t.i.d has been used in refractory cases.

Posterior fossa microvascular decompressive surgery has been used in drug-resistant cases.

Bell’s palsy (Idiopathic facial palsy)

Facial nerve or nerve sheath swell may be the reason of Bell’s palsy.

The cause is unclear, but it associated with cooling, viral infection (herps simplex virus type 1 in the geniculate ganglion) and diabetes.

Clinical Features

—Abruptly unilateral paralysis of muscles supplied by facial nerve, presenting with reduced wrinkling action, inability of closing the eye, loss of nasolabial fold, dropping of the side of mouth, weak cheek.

—Generally is preceded or accompanied by pain about the ear.

—Maybe accompanied impairment of taste, lacrimation or hyperacusis according to the lesion site.

—Physical examination: facial weakness, rare other abnormality.

Diagnosis

Exclude tumors that might compress the nerve.

Treatrnent

Most patients can recover spontaneously.

Prednisone: 60mg/d orally for 3 days, tapering over the next 7 days.

For patients who have a poor prognosis suggested by severe pain at onset and EMG evidence of denervation.

Acyclovir or other antiviral agents are not confirmed.

Acute inflammatory demyelinating Polyradiculoneuropathy (Guillain-Barre syndrome, GBS)

Introduction Acute/subacute onset Inflammatory demyelinating

polyradiculoneuropathy Symmetrical, progressive lower motor neurons

paralysis of limbs.

Etiology and Pathology

Commonly preceded by viral infection, vaccination to 1-4 weeks.

It appears to be an immunological basis. Pathological lesion are demyelinating on

anterior roots and peripheral nerves sometimes with axonal degeneration.

Clinical findings

1. Weakness: symmetrically begins with legs, usually severer in proximal than in distal of lower neurons lesion (hypotonia, hyporeflexia, wasting of affected muscles). The respiratory muscles palsy may be involved and cause respiratory failure, which is life threatening.

2. Sensory involvement: distal and symmetrical, as glove-and-stocking sensory loss, usually less marked than motor symptoms.

3. Cranial nerves involvement: produce ophthalmologic, facial palsy, bulbar palsy that predisposes to aspiration pneumonia.

oculormotor nerve: Ⅲ 、Ⅳ、Ⅵ facial nerve: Ⅷ bulbar palsy: Ⅸ 、Ⅹ4. Autonomic dysfunction: tachycardia, cardiac

irregularities, labile blood pressure, disturbed sweating, sphincter disturbance are rare.

5. CSF: albuminocytologic dissociation: a characteristic abnormality, with increased protein concentration but a normal cell count.

Diagnosis

Progressive weakness of more than one limb Distal or proximal hyporeflexia Relatively symmetrical deficit Mild sensory involvement Cranial nerve involvement Recovery beginning within 4 weeks after progression

stops Autonomic dysfunction No fever at onset CSF albuminocytologic dissociation Nerve conduction slowing or block by several weeks

Treatment

1. Plasmapheresis. May reduce the time required for recovery or decrease the likelihood of residual neurologic dificits.

2. Intravenous large dose of immunoglobulin 0.4g/kg/d for persistent 5~7 days appears to be equally effective. The two therapies are not additive.

3. Symptomatic therapy: closely monitor and assist respiration. If patient is short

of breath, the vital capacity falls below about 1L, blood oxygen saturation declines to 80% or oxygen pressure lower 70mmHg. The tracheotomy is necessary for patients with respiratory canal blocked by secretion or sputum.

Sometimes treatment with pressor agents is required to counter hypotension

Low-dose heparin may help to prevent pulmonary embolism.

4. Corticosteroids may affect the outcome adversely or delay recovery, and are not indicated.

Prognosis:

Self-limiting and cease to progress by about 4 weeks, improvement occurs over weeks or months following onset.

70-75% of patients recover completely, 25% are left with mild neurological deficits, and 5% die,usually as a result of respiratory failure.

Poor prognosis: Campylobacter jejuni infection, axonal degeration,more rapid onset of symptoms, the need for ventilatory support.