Peripheral neuropathy Flashcards
Functions of the PNS
- sensory input to the CNS
- Motor output to muscles
- innervation of viscera
Incoming sensory information enters via
Posterior root
Motor information exists via
Anterior root
Collection of nerve cell bodies is known as
ganglia
Layers in a peripheral nerve
- epineurium
- perienurium
- endoneurium
- axons
The vasa nervorium provides the blood supply.
Peripheral nerve trunks contain myelinated and unmyelinated fibres
Three different types of fibres
- Large myelinated fibres - motor nerves- proprioception, vibration and light touch
- Small myelinated fibres - light touch, pain and temperature
- Small unmyelinated fibres - light touch, pain and temperature
Pathogenesis of peripheral nerve degerenation
- Wallerian degeneration- this describes fibre degeneration when the fibre is cut or crushed. Both the axon and the myelin sheath will degenerate over several weeks after the incident
- Demyelination - Caused by inflammation( Guillain-Barre syndrome, post-diphtheric neuropathy, hereditary sensory-motor neuropathies) or by entrapment neuropathies - usually occurs as a result of schwann cell damage
Neuropathy
A pathological process that affects a peripheral nerve or nerves and may involve axonal degereation (wallerian) or demyelination
Mononeuropathy
Focal involvement of a single nerve
Polyneuropathy
Affects both sensory and motor neves (depending on the length). Diffuse disease affecting many nerves that is usually distal and symmetrical
Mononeuritis multiplex
Simulatenous or sequential development of nerves of 2 or more nerves
Radiculopathy
Affects nerve root
Plexoapthy
lesion within lumbar or cervical plexus
Sensory symptoms and signs
Negative (loss of sensation)
Large myelinated fibres - Loss of touch, vibration and joint position
- difficulty discriminating textures
- feet and hands feeling like cotton wool
- gait unstead
Small myelinated fibres - loss of pain, temerature appreciation
- painless burns and trauma
- damage to joints (charcots foot) resulting in painless deformity
Sensory symptoms and signs
positive symptoms
Large myelinated fibres - Causes parasthesia (pins and needles)
Small unmyelinated fibre disease - Painful positive symptoms
- burning sensation
- dysaesthesia: pain on gentle touch
- hyperalgesia: lowered threshold to pain
- Hyperpathia: pain threshold is elevared, but pain is excessively felt
- lightening pains: sudden, very severe, shooting pains
- allodynia: when a non painful stimuli becomes painful
Sensory examination
Large myelinated fibres:
- light touch
- two point discrimination
- vibration sense
- joint position sense
small unmyeinated fibres:
- temperature perception
- pain perception
When joint position is lost - rombergs test is positive (loss of joint-poisiton is compensated by vision, theregore, when eyes are closed, the stance becomes unsteady)
Sensory examination - neuropathic burns, trauma, ulcers, trophic changes due to loss of sensory and autonomic fibres
Autonomic symptoms
postural hypotension, erectile dysfunction, GI disturbance abnormal sweating
Clinical signs and symptoms of motor neuropathy
weakness, fasciculations, cramps and muscle wasting
Investigations
Neuropathy screen (bloods)
- -Fasting glucose (OGTT)
- -FBC
- -Urea and electrolytes
- Liver functions tests
- -Thyroid function tests
- -B12/folate
- -protein electrophoresis
Nerve conduction studies - differentiate axonal degeneration(reduced amplitude of electrical impulse) from demyelination (redeuced conduction veolcity) and can characterize whether motor or sensory fibres are involved
EMG: use of a fine needle inserted into a muscle can discern whether complete or partial denervation
Lumbar puncture:
-useful in inflammatory/paraneoplastic neuropathies (gullian-barre syndrome)
Nerves can be damaged by
- acute compression - by a tourniquet or tight fitting cast (tends to affect nerves that lie superficially to the skin)
- chronic compression - entrapment neuropathies
Mononeuropathy: Median nerve
Carpal tunnel syndrome
entrapment within carpal tunnel at wrist
Presenting symptoms :
- history of intermittent nocturnal pain, numbness and tingling- often relieved by shaking hand grip
- patient may complain of “weak grip”
- positive tinels sign
motor weakness:
- LOAF muscles (lumbricals, opponens pollicis, abuctor pollicis brevis, flexor pollicis brevis)
- weakness of thumb opposition, abduction, flexion
Sensory loss:
- palm and lateral three-and-a-half digitis
associations:
- pregnancy
- obesity
- hypothyroidism
- acromegaly
Treatment
- steroid injection to flexor retinaculum
- suurgical deecompression
Mononeuropathy: Ulnar nerve
-entrapment at ulnar groove (medial epicondyle of humerus)
Presenting symptoms
- history of trauma at elbow
- sensory disturbance and weakness “weak grip”
- usually painless
Motor weakness
- finger/pinkie/thumb abduction
- wrist flexion
Sensory loss:
- tingling or numbness affecting little finger, part of the ring finger and ulnar side of the hand distal to the wrist
- may extend to medial side of forearm
Mononeuropathy: Radial nerve compression
Saturday night palsy entrapment at spiral groove where the radial nerve is compressed against the humerus
Supploes the BEST (brachioradialis, extensors, supinator, wrist and tricepts
Presenting symptoms
- wrist and finger drop
- usually painless
Sensory
- region of anatomical snuffbox on the dorsum of the hand over the base and shafts of first two metcarpals
Treatment
- recovery is spontanoeus
Mononeuropathy: Common pereneal nerve
entrapment at fibular head
presenting symptoms:
- may be history of trauma, surgery or external compression
- acute onset foot drop + sensory disturbance on outside of calf
- usually painless
Motor weakness:
- ankle dorsiflexion, great toe extension
Causes:
- compression at the neck of the fibular head
- diabetes
- lepros
