SDL: Diseases of Skeletal Muscle and Peripheral Nerves

Question 1

type I muscle fiber characteristics

Answer 1

red, slow myosin, endurance, rich in mitochondria

Question 2

type II muscle fiber characteristics

Answer 2

white, fast myosin, strength and speed, rich in glycolytic enzymes and glycogen

Question 3

the delicate, barely visible connective tissue amongst the myofibers

Answer 3

endomysium

Question 4

“checkboard” distribution of white fibers vs dark fibers depends on..

Answer 4

the pH of the ATPase reaction, so its variable.

Question 5

board categories of muscle diseases and their differences

Answer 5

neurogenic (stems from nerve) atrophy, myopathic (steoms from muscle itself) atrophy

Question 6

progression of chronic denervation

Answer 6

normal muscle, motor unit loss with small group atrophy, collateral axonal sprouting, reinnervation, fiber type grouping with giant motor units, further motor unit loss with large group atrophy

Question 7

fiber type is decided by..

Answer 7

the neuron type innervating that particular myofiber

Question 8

denervated fibers have an _______ appearance

Answer 8

angulated atrophic

Question 9

what is fiber type grouping?

Answer 9

when the denervated orphan fiber is taken over by the other type of nerve fibers, they all become the same type.

Question 10

if its a nerve injury, the muscle remains at this stage from then on

Answer 10

collateral axonal sprouting, reinnervation, fiber type grouping

Question 11

if denervation is being caused by a disease, at some point..

Answer 11

the neuron innervating the large group of 1 type of fibers will also degenerate, leaving the entire group atrophic

Question 12

in early denervation, loss of motor units leads to

Answer 12

small angular fibers, involvement of both fiber types

Question 13

in chronic denervation, axonal sprouting and reinnervation leads to

Answer 13

large motor units, fiber type grouping

Question 14

in late denervation, loss of large motor units leads to

Answer 14

grouped atrophy

Question 15

in fiber type grouping, do you see checkerboard appearance?

Answer 15

no, because they are the same fiber type

Question 16

neurodegenerative disorder where neurons in the spinal cord are constantly degenerating

Answer 16

spinal muscular atrophies (motor neuron disease)

Question 17

disease of the neuromuscular junction where autoantibodies produced against ACh receptors on the post-synaptic membrane

Answer 17

myasthenia gravis

Question 18

pathology of myasthenic neuromuscular junction

Answer 18

simplified post synaptic folds to increase SA, compensatory proliferation of presynaptic vesicles;

Question 19

what does c. botulinum toxin block?

Answer 19

ACh release by interfering with the fusion proteins involved in membrane fusion between axon membrane and the synaptic vesicle membrane

Question 20

general myopathic changes

Answer 20

myofiber degeneration or regeneration, internalization of nuclei, increased endomysial connective tissue (scar), inflammation, vacuolation

Question 21

inherited myopathies examples

Answer 21

Duchenne’s and Becker (x-linked and autosomal)

Question 22

metabolic myopathies examples

Answer 22

lipid and glycogen storage diseases

Question 23

what causes ragged red fiber on muscle slides?

Answer 23

compensatory proliferation of mitochondria in mitochondrial disorders

Question 24

type II atrophy of muscle is seen with..

Answer 24

disuse, chronic disease, cachexia, corticosteroids

Question 25

*most important primary inflammatory myopathies

Answer 25

polymyositis, dermatomyositis, inclusion body myositis

Question 26

what is polymyositis?

Answer 26

autoimmune disorder involving infiltrates containing CD8 cytotoxic T cells; leads to myofiber necrosis

Question 27

what is dermatomyositis?

Answer 27

most common inflammatory myopathy in kids; autoimmune basis; can be paraneoplastic in adults

Question 28

what is inclusion body myositis?

Answer 28

most common inflammatory myopathy in patients 60 years and older; inflammation is probs a secondary event; could be a degenerative disease of aging specifically

Question 29

what is the pathology of polymyositis?

Answer 29

intrafascicular inflammation

Question 30

what is the pathogenesis of polymyositis? whats the clinical presentation?

Answer 30

cytotoxic T cell; pain

Question 31

what is the pathology of dermatomyositis?

Answer 31

extrafascicular inflammation; perifascicular atrophy

Question 32

what is the pathogenesis of dermatomyositis? what is the clinical presentation?

Answer 32

humoral; pain and rash

Question 33

what is the pathology of inclusion body myositis?

Answer 33

inclusions; rimmed vacuoles

Question 34

what is the pathogenesis of inclusion body myositis? the clinical presentation?

Answer 34

degenerative; steroid resistance

Question 35

where is the inflammation in dermatomyositis located?

Answer 35

in the perimysium, the connective tissue around the fascicle (the endomysium is within the fascicle)

Question 36

inclusion body myositis is represented by..

Answer 36

rimmed vacuole

Question 37

the muscular dystrophies

Answer 37

Duchenne MD, Becker MD, myotonic dystrophy

Question 38

Duchenne MD path characteristics

Answer 38

endoysial fibrosis with fiber (rounding), variation in fiber size, myofiber regeneration (small blue fibers)

Question 39

congenital myopathies (what are they named after?)

Answer 39

central core, rod body, centronuclear (they’re microscopic appearance)