PNS Clinical Considerations

Question 1

Class 1 Neurapraxia

Answer 1

• compression
• affected axons are demyelinated
• remyelination and conduction eventually resumes following removal of compression
• conduction is usually normal because the axon has not been disrupted
• usually temporary

Question 2

Class 2 Axonotmesis

Answer 2

• crush injury
• axonal disruption at the site of injury
• wallerian degeneration: lose part of axon and myelin distal to injury
• preservation of endoneurial tubes so this may mean nerves are able to be regenerated: helps growing nerve sprout to reach their previous terminals and hopefully a functional connection
• regenerate 1 mm/day and 1 in in a month so less distance to travel means faster healing

Question 3

Class 3 Neurotmesis

Answer 3

• severance of all neural and connective tissue components
• little hope of functional recovery without skilled surgery
• regenerating axons may enter inappropriate endoneurial tubes
• complex regional pain syndromes, severe pain, changes in sensation and skin
• look up to clarifyl

Question 4

Nerve Regeneration in PNS

Answer 4

• clean cut: nerve sprouting occurs within a few hours
• crush or tear: sprouting may delay for a week due to retrograde degeneration
• successful regeneration requires that the fibers make contact
• failure to re-approximate these fibers may lead to formation of a neuroma
• no clear path means aberrant, abnormal growth
• step 1: proximal stump-multiple growth cones branch out
• step 2: simultaneously distal Schwann cells send out processes (filopodia) toward proximal stump and exert traction pull on the growth cones
• step 3: growth cones are mitogenic to Schwann cells
• filopodia recognize Schwann cells previously occupied by axons of a similar kind
• muscle atrophies and remains viable for 2 years
• during this time it is undergoing fibrosis: 30% atrophy in first month; 50-60% by 2 months; 60-80% by 4 months (stabilizes)
• functional re-innervation diminishes if the axon does not reach endplate within 12 mo of denervation

Question 5

Nerve Regeneration in CNS

Answer 5

• distal degeneration occurs in a similar manner to the PNS
• slower clearance of debris by microglial cells and monocytes
• debris can be identified up to 6 months after an injury, whereas it is gone in 6 days in the PNS
• chromatolysis (change in cell body) is rare
• general rule = large scale neuron death, survivors are atrophied with permanent isolation from synaptic contacts
• transneuronal atrophy: CNS neurons have trophic affect upon each other, helper molecules help nerve make connections with neighbors
• small CNS lesion: neuronal debris replaced by glial scar tissue-primarily astrocytes
• large CNS lesion: scar tissue causes region to wall off and form cystic cavity containing CSF and blood
• neurons in CNS of humans do not regenerate axons, or at least do not do so effectively
• injured motor and sensory pathways do not re-establish their original connections
• regenerate only a few mm at most
• deterrents to spontaneous regeneration: obstruction by glial scar tissue, growth inhibition byproducts of the broken down oligodendorcytes

Question 6

Ulnar Nerve Palsy

Answer 6

• elbow, wrist, brachial plexus, hand atrophy

- stimulate nerve and try to get them to move hand

Question 7

Erb’s Palsy

Answer 7

• pulling on baby to get out of birth canal may lead to shoulder dystocia
• stretching of brachial plexus-difficult time delivering shoulder during birth –> traction to get out –> stretched plexus –> paralysis of 1 arm usually affects C5, loos of fx of biceps, deltoid, brachialis –> IR –> inhibits flexion and supination

Question 8

Hand Palsy

Answer 8

• wrist drop (radial palsy)
• preachers hand (median palsy)
• ulnar claw (ulnar palsy)
• simian hand (median and ulnar palsy)

Question 9

Myasthenia Gravis

Answer 9

• severe muscle weakness
• immune system produces antibodies which bind to ACH receptors interfering with the normal action of ACH: autoimmune disease
• muscles most affected are those supplied by cranial nerves: face, mouth, eyes and limbs, especially proximal
• often see optic deficits
• swallowing and respiratory weakness may be life threatening
• anti ACHesterase drugs
• thymectomy

Question 10

Nerve Root Compression

Answer 10

• most frequently occurs where spine is most mobile (cervical and lumbar) either by spondylosis or HNP
• pain perceived/produced in myotome, sclerotome, and/or dermatome distributions
• dermatome: paresthesias, sensory loss
• myotome: motor weakness, loss of a tendon reflex
• discs degenerate as you age and sometimes inner part will come out and press on nerve root –>pain/weakness in dermatome, myotome, sclerotome

Question 11

Guillain Barre Syndrome

Answer 11

• leg weakness noted first
• may be precipitated by respiratory infection, gastric infection, surgery, immunization
• immune system attacks body
• can be induced by a flu shot