Peripheral Nervous System

Question 1

axonal neuropathy

Answer 1

lose axons

Question 2

demyelinating neuropathy

Answer 2

lose Schwann cells

Question 3

mononeuropathy

Answer 3

affects one neuron

Question 4

polyneuropathy

Answer 4

affects multiple neurons

Question 5

mononeuropathy multiplex

Answer 5

multiple mononeuropathies (more rare)

Question 6

two ways to test for neuromuscular disease

Answer 6

elctromyography - examine spontaneous and evoked electrical activity in skeletal muscle

nerve conduction velocity - measure velocity and amplitude of compound APs

Question 7

What does a demyelinating neuropathy do to compound APs

Answer 7

If some axons are myelinated and some aren’t, axons are still intact but since fewer axons have fast APs, the overall conduction velocity is reduced

(CONDUCTION VELOCITY REDUCED, AMPLITUDE DISPERSED)

Question 8

What does an axonal neuropathy do to compound APs?

Answer 8

CONDUCTION VELOCITY NORMAL, AMPLITUDE REDUCED

since some of axons are gone, signal still travels at the same velocity, but there is less signal

Question 9

What kinds of neuropathies are typically seen in axonal neuropathies?

Answer 9

Most toxic/metabolic neuropathies (ex: diabetes patients will often show polyneuropathies, alcohol poisoning)

Question 10

What are two examples of diseases that are demyelinating neuropathies?

Answer 10

Guillan Barre syndrome (acquired, proteins turn on peripheral myelin which will transiently attack Schwann cells -> develops polyneuropathy)

Charcot Marie tooth disease - genetic, defected myelination

Question 11

What nerve is “harmless” enough to do a high risk nerve biopsy on? (nerve biopsies tend to have high risk for nerve dysfunction)

Answer 11

the sural nerve (only for sensory neuropathies) (in the foot)

you don’t want to do this on a useful nerve

Question 12

onion bulb formation

Answer 12

Seen in demyelinating neuropathy (where are bunch of Schwann cells surround an axon and try to repeatedly remyelinate and demyelinate it ineffectively….cause nerve to dilate, almost palpable)

seen in Charcot Marie tooth disease

Question 13

Two types of disorders affecting NMJ?

Answer 13

myastehnia gravis - autoimmune, thymic abnormalities, clear antibodies to treat

organophosphate intoxication - inhibit AchE, increase synaptic action of Ach, nerve gases, irreversible, very toxic (ex: sarin)

Question 14

How to treat and dx myasthenia gravis?

Answer 14

treat - pyridostigmine (long acting reversible)

dx - edrophonium (very short acting)

Question 15

Difference between type I and type II muscle fibers (histologically)

Answer 15

type I - dark red, oxidative
type II - light white, glycolytic

“RED, WHITE, BLUE”

fiber type is dependent on innervating neuron

Question 16

What happens when muscle fibers lose their innervation?

Answer 16

They shrink/atrophy, then spread Ach all over diffusely (help me help me signal)

Question 17

When a neuron dies, what do surrounding surviving neurons do?

Answer 17

A surviving neuron adopts the “orphaned/abandoned” fibers leading to type grouping

(de-innervation to re-innervation)

Question 18

Type grouping

Answer 18

Usually, type I and type II fibers are scattered like a mosaic, but when fibers become de-innervated and subsequently re-innervated…they form clusters of of like type fibers. Good indicator of atrophy

Question 19

What can indicate a progressive neurologic problem?

Answer 19

De-innervation, then re-innervation (type grouping), then de-innervation again (death of neuron that took up orphaned fibers)

Question 20

How can you classify muscle biopsy findings?

Answer 20

1. neurogenic - type goruping, group atrophy, angular fibers, target fibers
2. myopathic - fiber size variability, basophilia, central nuclei, splitting, macrophages, fibrosis

Question 21

Two types of myopathy?

Answer 21

degenerative - dystrophy

inflammatory - myositis

Question 22

Dystrophin

Answer 22

subsarcolemmal structural protein, located on X chromosome (disorders more common in males), X- linked recessive

Question 23

Duchenne’s dystrophy vs. Becker’s

Answer 23

Duchenne’s - severe, early onset, rapid progression

Becker’s - milder, later onset, slower progression

all linked to dystrophin mutation!

Question 24

difference in weakness in myopathies and neuropathies

Answer 24

myopathies - weakness proximally (trunk, limbs)

neuropathies - weakness distally

Question 25

Characteristics of myotonic dystrophy

Answer 25

autosomal dominant, trinucleotide repeat amplification, myotonia (impaired muscle relaxation), distal wasting, balding, endocrine abnormalities

Question 26

myotonia

Answer 26

impaired muscle relaxation

Question 27

Where are the nuclei seen in muscles with myotonic dystrophy?

Answer 27

INTERNAL NUCLEI, abnormal

Question 28

2 types of inflammatory myopathy?

Answer 28

polymyositis - lymphocitic infiltration, muscle fiber destruction, PAIN and weakness, AUTOIMMUNE so treat with IMMUNOSUPPRESSION

inclusion body myositis - all the same except no pain while weak, not effective with immunosuppression, rimmed vacuoules

Question 29

Classifications of myopathy?

Answer 29

dystrophy, inflammatory, congenital (structural protein disorders presenting in infancy or early childhood), metabolic, mitochondrial (genetic, maternally inherited, depends where bad mitochondria end up)

Question 30

neuropathy vs. myopathy

Answer 30

neuropathy - distal weakness, reduced reflexes, sensory loss, dysesthesiae, muscle wasting, fasiculations (involuntary muscle twitching)

myopathy - PROXIMAL weakness, reflexes PRESERVED, no sensory loss, muscle pain, wasting is UNCOMMON, NO fasiculations, may have myotonia