Lecture 31: MSK 4

Question 1

Compare the 3 muscle types

Answer 1

cardaic: striated and involuntary

smooth: non-striated and involuntary

skeletal: striated and voluntary

Question 2

What is another name for muscle cell

Answer 2

myofibre

Question 3

What are the features of a muscle cell

Answer 3

multinucleated with a peripheral nuclei

terminally differentialted = no cell division

different types have different contractile properties

depend on innervating neurons

Question 4

What cells do myofibres come from

Answer 4

myoblasts aka satellite cells

Question 5

What is a myofibril

Answer 5

collection of myofilaments

Question 6

What is a myofilament

Answer 6

collection of myofibres

Question 7

What is a motor unit

Answer 7

spinal nerve and all the muscle fibres it connects to

causes simultaneous contraction of the all the muscle cells in the unit

Question 8

What are the 3 types of reactions muscle has to injury

Answer 8

gross appearance:
- change in mass/shape/colour

growth change

muscle necrosis

Question 9

What is a physiologic cause for pallor in muscle

Answer 9

young

Question 10

What is a cause for green in muscle (non pathogenic)

Answer 10

putrifaction

Question 11

What is a non pathogenic cause for black in muscle

Answer 11

melanosis of fascia

Question 12

What is a non pathogenic cause for dark red muscle

Answer 12

hypostatic congestion artifact

hemorrhage

rhabdomyolysis

Question 13

What changes might you see grossly in muscle that is a response to injury

Answer 13

change in mass

shape change

colour change

mineralization

parasites (cysts)

Question 14

What are 3 types of growth cahgnes that can occur in response to muscle injury

Answer 14

atrophy: reduce muscle mass duue to reduced size/diameter of muscle fibre

hypertrophy: reversible increase in size/siameter of muscle fibres

hyperplasia: increased number of muscle fibres

Question 15

What are 4 causes for muscle atrophy

Answer 15

disuse: reduce type 2 fibre

dennervation/neurogenic: rapid atrophy of type 1 or 2 fibres
- if chronic it also has steatitis and fibrosis

malnutrition/cachexia: reduce type 2 fibres

endocrine dz: reduce type 2 fibres
- cushing/hypothyroid

Question 16

What are the 2 classifications of muscle necrosis

Answer 16

segmental aka zenker degeneration
- muscle cell partially dies but not fully because it is multinucleated

global: complete death of muscle cell

Question 17

What are the histologic changes that accompany muscle necrosis

Answer 17

myofibril swelling

loss of striation

vacuolation and fragmentation of cytoplasm

mineralization (due to lot of Ca in sarcoplasmic reticulum)

Question 18

What are 4 requirements for muscle regeneration

Answer 18

satellite cells

intact basal lamina

blood supply

removal of necrotic debris

Question 19

List the 3 steps of muscle regeneration

Answer 19

macrophage infiltration to remove the debris
- require a blood supply

satellite cells activate and proliferate

now myoblasts fuse and form regenerating myotubules

Question 20

List the 4 types of muscle injury

Answer 20

focal monophasic

focal polyphasic

multifocal monophasic

multifocal polyphasic

monophasic = 1 incident
- all muscle at same stage of injured

polypahsic: repeat injury
- multiple different stages of muscle regeneration or degeneration

Question 21

List 5 types of congenital myopathy

Answer 21

congenital muscular hyperplasia

muscular dystrophy

myotonic spastic syndrome

metabolic myopathy

malignant hyperthermia

Question 22

What is congenital muscular hyperplasia and what causes it?

Answer 22

aka double muscling

due to a myostating gene mutation

causes increase in number of muscle fibres (normal size)

Question 23

What animals are commonly affected by congenital muscular hyperplasia

Answer 23

belgian blue

whippet

Question 24

What is muscular dystrophy and what causes it

Answer 24

ongoing necrosis and regeneration

inherited x linked condition
- mutation of dystrophin gene

Question 25

What animal is primarily affected by muscular dystrophy and what is a common clinical presentation

Answer 25

dogs plantigrade stance

Question 26

What is myotonic and spastic syndrome and what causes it

Answer 26

temporary inability of muscle contraction due to a plasma membrane defect in the Cl channels

Question 27

What are 2 examples of species specific conditions of myotonic and spastic syndrome

Answer 27

fainting goats hyperkalemic period paralysis

Question 28

What animals does hyperkalemic period paralysis affect and what does it present as? What causes it?

Answer 28

quarter horses transient paralysis/hypotonia due to a autosomal dominant mutation in the Na channel

Question 29

What are 2 conditions that cause metabolic myopathy

Answer 29

glycogen storage dsiease equie polysaccharide storage myopathy

Question 30

What is glycogen storage disease? Why does it occur?

Answer 30

abnormal skeletal muscle energy metabolism resulting in excessive carb/lipid storage due to inadequate energy production from (potentially) a mitochondrial defect

Question 31

What are the clinical signs of glycogen storage disease causing metabolic myopathy

Answer 31

weakness exercise induced cramps rhabdomyolysis

Question 32

What animals are affected by equine polysaccharide storage myopathy

Answer 32

drafts warmblood arabian quarter

Question 33

What is equine polysaccharide storage myopathy?

Answer 33

It is a carbohydrate disorder causing intracellular glycogen accumulation

Question 34

What is malignant hyperthermia and what causes it

Answer 34

Caused by ryanodine receptor defect resulting in increased intracellular Ca - causes prolonged muscle contraction leading to hyperthermia

Question 35

What are the gross signs of malignant hyperthermia? What animals are primarily affected?

Answer 35

pigs and dogs pale/soft/exudative muscle (PSE pork) fast onset of rigor mortis can cause acute heart failure

Question 36

What is a main cause of nutritional myopathy? How does the disease differ between cows, pigs, and horses?

Answer 36

vit E and selenium deficiency cow: white muscle pig: mulberry heart disease and hepatosis dietetica horse: yellow fat dz

Question 37

What are the gross lesions associated with white muscle disease

Answer 37

pale muscle +/- mineralization brushstroke lesions on the endo and epicardium - preferentially in the LV (vs RV) - concurrent acute heart failure skeletal and cardiac lesions are not always together

Question 38

What are 2 toxin types that can cause a myopathy

Answer 38

ionophores myotoxins

Question 39

What animals are affected by ionophores? What are the gross lesions?

Answer 39

horses (contamination of feed with ruminant or poultry feed) acute muscle necrosis = hemorrhagic or pale +/- skeletal muscle and myoglobinuria

Question 40

What is a myotoxin affecting pigs

Answer 40

gossypol (cotton seed)

Question 41

What is are 2 myotoxins affecting horses

Answer 41

seasonal pasture myopathy box elder tree

Question 42

What is senna

Answer 42

a myotoxin from coffee bean senna

Question 43

What type of muscle injury do myotoxins cause

Answer 43

multifocal and polyphasic

Question 44

What are 2 types of exertional myopathy

Answer 44

exertional rhabdomyolysis capture myopathy

Question 45

What are the clinical signs of exertional rhabdomyolysis

Answer 45

rhabdomyolysis = skeletal muscle necrosis myoglobinuria (red wine urine)

Question 46

What causes exertional rhabdomyolysis? What animals does it affect? What are some alternate names for this condition?

Answer 46

horses and dogs exercise stress black disease/monday morning disease/tying up/azoturia

Question 47

What animals does capture myopathy affect? What is the cause

Answer 47

wildlife due to stress causing acute death

Question 48

What are 2 conditions that cause a circulatory myopathy

Answer 48

compartment syndrome downers syndrome

Question 49

What is compartment syndrome? What causes it?

Answer 49

increased intramuscular pressure in non expandable compartment increased vascular skeletal muscle along with occlusion of large blood vessels or severe intramuscular vascular injury

Question 50

How does compartment syndrome affect muscle cells? What animal is this common in? How is it commonly treated?

Answer 50

ischemia - varied susceptibility most susceptible: muscle fibre > satellite cell > fibroblasts deep pectoral myopathy in chickens tx: early fasciotomy to reduce pressure

Question 51

What is downer syndrome? What animals does it affect most?

Answer 51

increased intramuscular pressure due to body weight pressure cow and horse

Question 52

What are the sequelae of downer syndrome

Answer 52

Ischemic necrosis reperfusion injury

Question 53

What are 3 types of neuromuscular dysfunction causing myopathy

Answer 53

myesthenia gravis botulism tetanus

Question 54

Compare myopathy due to neuromusclar injury and dennervation atrophy

Answer 54

neuromuscular injury - failure of signal transmission - innervation intact dennervation atrophy - lack of innervation of tissueW

Question 55

What causes botulism

Answer 55

clostridium botulinum

Question 56

What causes tetanus

Answer 56

clostridium tetani

Question 57

Compare the clinical consequence of botulism and tetanus

Answer 57

botulism - flaccid paralysis (prevention of presynaptic Ach) tetanus - spastic paralysis (prevention of inhibitory neurons)

Question 58

What are 3 main causes of myositis

Answer 58

suppurative myositis clostridial myositis parasitic myositis

Question 59

What is the route of infection causing suppurative myositis? What is a primary gross lesion

Answer 59

blood borne or direct innoculation causes intramuscular abscesses

Question 60

What are 2 common animals that get suppurative myositis? What is the typical causative agents?

Answer 60

horses: in pectoralis - Cornybacterium pseudotuberculosis - strep equi cow: truperella pyogenes

Question 61

What are the features of clostridia bacteria

Answer 61

gram + spore forming (environmentally stable) commensal (except C. chauvei) many species

Question 62

List 2 diseases caused by clostridial myositis? What is the causative agent?

Answer 62

malignant edema: C. septicum black leg: C. chauvei

Question 63

Compare the clinical signs of malignant edema and black leg

Answer 63

malignant edema: swelling and edema in muscle black leg: dark red bubbles in muscle with crepitus and rancid butter smell sporulated and encysts in muscle causing muscle necrosis anaerobic environments (due to muscle necrosis) allow growth

Question 64

List 3 common causes of parasitic myositis and the causative agent of each

Answer 64

trichenollosis: larval nematode (zoonotic) cysticercosis: taniae tapeworm (zoonotic) sarcocystis: protozoa (incidental)

Question 65

List 2 causes of non infectious causes of myositis? What type of diseases are they?

Answer 65

auto immune masticatory muscle myositis polymyositis

Question 66

What is masticatory muscle myositis? What animal does it affect?

Answer 66

dogs - GSD chewing muscle (massetor) inflammation - unique to canine mastecatory muscles

Question 67

What is polymyositis? What animal does it mainly affect?

Answer 67

dogs - GSD generalized myositis

Question 68

Contrast masticatory muscle myositis and polymyositis

Answer 68

masticatory muscle myositis: - caused by auto antibody against 2M myosin which is unique to canine mastecatory muscle polymyositis - no 2M myostin anti-antibody

Question 69

What are the main types of primary muscle neoplasia

Answer 69

rare usually from satellite cells rhabdomyoma rhabdomyosarcoma

Question 70

List 2 types of secondary muscle neoplasias

Answer 70

uncommon melanoma infiltrative lipomas