L48 PNS Disorders

Question 1

define paresthesias.

Answer 1

a morbid or abnormal sensation, as burning, prickling, pins and needles, numbness

Question 2

define ephapse.

Answer 2

pathological contact between parallel nerve fiber where electrical nerve impulses can “leak” from one fiber to the other

Question 3

What are negative manifestations?

Answer 3

• 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

Question 4

what is the cause of negative manifestations?

Answer 4

conduction failure in efferent and/or afferents

Question 5

what are positive manifestations?

Answer 5

• 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

Question 6

what is the conduction of velocity formula?

Answer 6

conduction velocity = D/(T1-T2) for sensory and motor!

Question 7

what is the mean conduction velocity for sensory and motor nerves?

Answer 7

55 m/s

Question 8

What type of CV measurement do you see with a lesion at the motor neuron soma?

Answer 8

slight/no change in motor

no change in sensory

Question 9

What type of CV measurement do you see with a lesion at peripheral nerve specifically with demyelination?

Answer 9

REDUCTION of motor + sensory

Question 10

What type of CV measurement do you see with a lesion at peripheral nerve specifically with compression?

Answer 10

slowing of motor + sensory AT THE SITE

Question 11

What type of CV measurement do you see with a lesion at peripheral nerve specifically with axonal degeneration?

Answer 11

no/slight reduction

Question 12

What type of CV measurement do you see with a lesion at NMJ?

Answer 12

no change in motor + sensory

Question 13

What type of CV measurement do you see with a lesion at muscle?

Answer 13

no change in motor + sensory

Question 14

what are examples of mechanical trauma to nerves?

Answer 14

• compression, stretching (carpal tunnel syndrome)
• crush
• axotomy

*note - the smaller the structure is, the more vulnerable it is to damage

Question 15

what is CV measurement used to rule in or out?

Answer 15

can detect demyelinating diseases

Question 16

what is the most vulnerable part of the peripheral nerve?

Answer 16

axon covered in endoneurium (within fascicles surrounding small clusters of axons)

Question 17

what is the least vulnerable part of the peripheral nerve?

Answer 17

epineurium (outer covering of the entire nerve)

Question 18

what does the perineurium cover?

Answer 18

covers each fascicle

Question 19

Describe carpal tunnel syndrome

Answer 19

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

Question 20

what are risk factors for carpal tunnel syndrome?

Answer 20

women (middle aged)
pregnancy
hypothyroidism
elderly

Question 21

what does the carpal tunnel contain?

Answer 21

tendon of FPL, long finger flexors and median nerve

Question 22

what happens in a crush injury?

Answer 22

there is extensive damage to musculature and nerve

you will see LOTS of edema!

Question 23

define axotomy?

Answer 23

nerve injury with ruptured or cut axons that yields many consequences

Question 24

what are some of the consequences of axotomy?

Answer 24

wallerian degeneration
anterograde transneural degeneration
retrograde transneural degeneration

Question 25

what is Wallerian degeneration?

Answer 25

degeneration of the axon distal to injury

Question 26

what is anterograde transneural degeneration?

Answer 26

degeneration of nerve cells distal to injury retraction of synaptic terminals proximal to injury chromatolysis seen

Question 27

What is chromatolysis

Answer 27

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.

Question 28

what is retrograde transneural degeneration

Answer 28

degeneration of nerve cells proximal to the injury chromatolysis seen *this is seen in ALS (Lou Gehrig's disease)

Question 29

axonal sprouts may use lingering ______ of the degenerated axons as guide tubes for regrowth

Answer 29

Schwann cells

Question 30

when does of the probability of successful regrowth increase?

Answer 30

when the site of injury is nearer to the original target

Question 31

in Bell's palsy, there is sometimes regeneration error seen in peripheral nerves. What is an example of this?

Answer 31

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!

Question 32

what facilitates axonal regrowth?

Answer 32

nerve growth factor

Question 33

what releases nerve growth factor

Answer 33

Schwann cells, laminins and adhesion molecules

Question 34

the axonal sprout may grow at a rate of _____

Answer 34

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!

Question 35

why don't axons in the CNS regenerate?

Answer 35

- 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

Question 36

following nerve damage, motor axons may regenerate and form new ____

Answer 36

NMJ

Question 37

the regenerating axons differentiate into _____ when they contact the basal lamina

Answer 37

nerve terminals

Question 38

components of the _____ facilitate rein nervation of the synaptic sites and trigger differentiation of axonal growth cones into presynaptic nerve terminals

Answer 38

basal lamina

Question 39

what is necessary in the formation of functional NMJ

Answer 39

basal lamina

Question 40

what are the different laminins that exist in the basal lamina

Answer 40

laminin 11 - synaptic + extrasynaptic basal lamina | laminin 2 - extrasynaptic basal lamina

Question 41

Describe Guillain-Barre syndrome (acute idiopathic polyneuritis, infectious polyneuritis, acute inflammatory polyneuropathy)

Answer 41

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

Question 42

how is Guillain-Barre syndrome diagnosed?

Answer 42

lumbar puncture - find elevated protein in CSF (100-300 mg/dl) NCV (nerve conduction velocity) - sensitive to demyelination EMG - lack of nervous stimulation

Question 43

what is the treatment for Guillain-Barre syndrome?

Answer 43

``` immune globulin (IV) 0.4 g/kg plasmapheresis (plasma exchange) ventilatory support ```

Question 44

what is the cause of Guillain-Barre syndrome?

Answer 44

acute nerve inflammation damages the myelin sheath conduction and impulses through the nerve is slow/blocked = muscle weakness, paralysis and sensory loss result

Question 45

what are the complications associated with Guillain-Barre syndrome

Answer 45

respiratory failure aspiration pneumonia DVT

Question 46

describe Leprosy (Hansen disease)

Answer 46

- 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

Question 47

describe lead poisoning

Answer 47

``` 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 ```

Question 48

describe alcoholic peripheral neuropathy

Answer 48

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

Question 49

describe polyneuropathy in DM

Answer 49

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