L48 PNS Disorders Flashcards
define paresthesias.
a morbid or abnormal sensation, as burning, prickling, pins and needles, numbness
define ephapse.
pathological contact between parallel nerve fiber where electrical nerve impulses can “leak” from one fiber to the other
What are negative manifestations?
- muscle weakness (paresis)
- loss of tendon reflexes
- autonomic nerouvs deficits (eg. anhydrosis)
- impaired sensations (eg. pain and temperature loss)
*lose your strength and become weak
what is the cause of negative manifestations?
conduction failure in efferent and/or afferents
what are positive manifestations?
- Fasciculations - unpredictable activity in path motor units
- paresthesias (tingling, numbness and pins and needles) - may reflect ephaptic transmission between adjacent damaged sensory nerve fibers that have become hyperexcitable
- brief periods of pain (eg. trigeminal neuralgia, carpal tunnel syndrome) - prob causes by acute periods of compression of nerves that produce brief hyperexcitabiliy
what is the conduction of velocity formula?
conduction velocity = D/(T1-T2) for sensory and motor!
what is the mean conduction velocity for sensory and motor nerves?
55 m/s
What type of CV measurement do you see with a lesion at the motor neuron soma?
slight/no change in motor
no change in sensory
What type of CV measurement do you see with a lesion at peripheral nerve specifically with demyelination?
REDUCTION of motor + sensory
What type of CV measurement do you see with a lesion at peripheral nerve specifically with compression?
slowing of motor + sensory AT THE SITE
What type of CV measurement do you see with a lesion at peripheral nerve specifically with axonal degeneration?
no/slight reduction
What type of CV measurement do you see with a lesion at NMJ?
no change in motor + sensory
What type of CV measurement do you see with a lesion at muscle?
no change in motor + sensory
what are examples of mechanical trauma to nerves?
- compression, stretching (carpal tunnel syndrome)
- crush
- axotomy
*note - the smaller the structure is, the more vulnerable it is to damage
what is CV measurement used to rule in or out?
can detect demyelinating diseases
what is the most vulnerable part of the peripheral nerve?
axon covered in endoneurium (within fascicles surrounding small clusters of axons)
what is the least vulnerable part of the peripheral nerve?
epineurium (outer covering of the entire nerve)
what does the perineurium cover?
covers each fascicle
Describe carpal tunnel syndrome
occurs spontaneously!
compression of the medial nerve passing from the forearm into the narrow carpal tunnel at the wrist
sometimes the tendon develops an irritations or swelling, causing the carpal tunnel to narrow even further, compressing the median nerve (maybe due to overuse or from soft tissue swelling due to edema)
weakness, pain and numbness affecting the hand and wrist will accompany pain that often radiates up the arm
causes difficulty handling small objects (maybe wasn’t got abductor brevis and opponents pollicis) and muscular atrophy of the thenar eminence
what are risk factors for carpal tunnel syndrome?
women (middle aged)
pregnancy
hypothyroidism
elderly
what does the carpal tunnel contain?
tendon of FPL, long finger flexors and median nerve
what happens in a crush injury?
there is extensive damage to musculature and nerve
you will see LOTS of edema!
define axotomy?
nerve injury with ruptured or cut axons that yields many consequences
what are some of the consequences of axotomy?
wallerian degeneration
anterograde transneural degeneration
retrograde transneural degeneration
what is Wallerian degeneration?
degeneration of the axon distal to injury
what is anterograde transneural degeneration?
degeneration of nerve cells distal to injury
retraction of synaptic terminals proximal to injury
chromatolysis seen
What is chromatolysis
is the dissolution of the Nissl bodies in the cell body of a neuron. It is an induced response of the cell usually triggered by axotomy, ischemia, toxicity to the cell, cell exhaustion, virus infections, and hibernation in lower vertebrates.
what is retrograde transneural degeneration
degeneration of nerve cells proximal to the injury
chromatolysis seen
*this is seen in ALS (Lou Gehrig’s disease)
axonal sprouts may use lingering ______ of the degenerated axons as guide tubes for regrowth
Schwann cells
when does of the probability of successful regrowth increase?
when the site of injury is nearer to the original target
in Bell’s palsy, there is sometimes regeneration error seen in peripheral nerves. What is an example of this?
some nerves regenerate and travel to buccal area
some nerve regenerate and accidentally travel to eye
so if you tell that pt a joke, they will attempt to smile but they may wink at you instead!
what facilitates axonal regrowth?
nerve growth factor
what releases nerve growth factor
Schwann cells, laminins and adhesion molecules
the axonal sprout may grow at a rate of _____
1 mm per day!
slow process
if you have a lesion 30cm away, it will take a year for nerve to heal
after regeneration, Schwann cells redevelop and CV may increase!
why don’t axons in the CNS regenerate?
- oligodendrocytes do not release growth factor nor guide regenerating axonal sprouts
- GLIOSIS occurs - astrocyte multiply in regions of trauma and form a scar that mechanically impedes sprouting axons
- chemical signaling may also oppose axonal regeneration in the adult
following nerve damage, motor axons may regenerate and form new ____
NMJ
the regenerating axons differentiate into _____ when they contact the basal lamina
nerve terminals
components of the _____ facilitate rein nervation of the synaptic sites and trigger differentiation of axonal growth cones into presynaptic nerve terminals
basal lamina
what is necessary in the formation of functional NMJ
basal lamina
what are the different laminins that exist in the basal lamina
laminin 11 - synaptic + extrasynaptic basal lamina
laminin 2 - extrasynaptic basal lamina
Describe Guillain-Barre syndrome (acute idiopathic polyneuritis, infectious polyneuritis, acute inflammatory polyneuropathy)
rapidly ascending motor and sensory loss 2-3 weeks after respiratory or GI illness - demyelination of peripheral nerves
autoimmunity implicated!
good recovery following, remyelination occurs in PNS
incidence: 2/100,000
more common in men than women
how is Guillain-Barre syndrome diagnosed?
lumbar puncture - find elevated protein in CSF (100-300 mg/dl)
NCV (nerve conduction velocity) - sensitive to demyelination
EMG - lack of nervous stimulation
what is the treatment for Guillain-Barre syndrome?
immune globulin (IV) 0.4 g/kg plasmapheresis (plasma exchange) ventilatory support
what is the cause of Guillain-Barre syndrome?
acute nerve inflammation damages the myelin sheath
conduction and impulses through the nerve is slow/blocked
= muscle weakness, paralysis and sensory loss result
what are the complications associated with Guillain-Barre syndrome
respiratory failure
aspiration
pneumonia
DVT
describe Leprosy (Hansen disease)
- commonest treatable neuropathy
- infection of skin and peripheral nerves with mycobacterium leprae
- LONG incubation period!
- bacterial entry through skin lesions often following contact with nasal secretions from infected persons
- enters unmyelinated areas (somatosensory - loss of pain sensation?)
- bacterial multiplication causes compression and ischemia of all peripheral axons
- profound sensory losses (pain and temp)
- multidrug antibiotic tx usually successful
describe lead poisoning
motor neuropathy in adult encephalopathy in infants attacks the brain in children NO sensory symptoms bilateral focal weakness and wasting of EXTENSOR muscle of fingers, wrist and arms
describe alcoholic peripheral neuropathy
sensory + motor losses = symmetrical
starts with sensory neuropathy (foot… leg)
later motor losses starting at lower leg
NCV in most cases NORMAL
more than 80-100 g alcohol/day
vitamin B1 (thiamin) deficiency related to malnutrition
describe polyneuropathy in DM
sensory - symmetric
motor - asymmetric
autonomic (culminating in dry skin)
sensory symptoms begin in both legs as ‘stocking distribution’
vulnerable to hyperglycemia - sensory endings and axons of small unmyelinated DRG cells
problem may originate in the failure of the cell body to supply its distal parts with nutrients and essential proteins for its cytoskeleton
cases often complicated by diabetic vasculopathies
