Skeletal muscle

Question 1

Cause of denervation atrophy

Answer 1

caused by lost connection to peripheral nerves

- unaffected motor neuron has compensatory hypertrophy

Question 2

Type 1 muscle fiber v. type 2

Answer 2

type 1- slow (marathon runner)

Type 2- fast twitch (sprinter)

Question 3

Cause of disuse atrophy

Answer 3

decreased contractile activity of innervated muscles causing a uniform atrophy (ex. painful lameness, fx, bone disease)

Question 4

Cause atrophy from malnutrition/cachexia

Answer 4

caused by inability to support dietary nutrition to maintain muscle mass~ causes generalized atrophy
- cachexia is associated with neoplasia & chronic illness

Question 5

Cause atrophy of endocrine disease

Answer 5

associated with hypothyroidism & hyperglucocorticoidism

i. Primarily selective type 2 atrophy with no compensatory type 1 hypertrophy

Question 6

myopathic atrophy

Answer 6

muscle atrophy after primary muscle disease (ex. inflammatory muscle disease)

Question 7

4 different patterns of myofiber necrosis

Answer 7

Focal monophasic rxn- infarct
Multifocal monophasic rxn- toxin
Focal polyphasic rxn- repeat injury/same site
Multifocal polyphasic rxn- nutritional myopathies

Question 8

What gene is responsible for “double muscling”

Answer 8

defective myostatin gene affecting cattle, dogs & sheep

Question 9

What is muscular dystrophy?

Answer 9

X-linked recessive disorder caused by defects in the gene encoding dystrophin.

Question 10

hyperkalemic periodic paralysis (HYPP) disease mechanism

Answer 10

ion channel defect affecting sodium channel (muscle) that alters muscle membrane potential.

Question 11

HYPP clinical signs

Answer 11

muscle fasciculations (spams), 3rd eyelid flashing, collapse

Question 12

Best way to confirm HYPP

Answer 12

DNA testing

Question 13

What breeds are predisposed to polysaccharide storage myopathy

Answer 13

draft horses, warmbloods & quarter horses

Question 14

CS of PSM

Answer 14

recurrent exertional rhabdomyolysis–> progressive weakness

Question 15

What gene is associated with the PSM?

Answer 15

mutated GYS1

Question 16

Mechanism of congenital myasthenia gravis

Answer 16

inherited defect in acetylcholine end plate receptor (autosomal recessive in dogs)

Question 17

Mechanism of acquired myasthenia gravis

Answer 17

circulating antibodies to motor end plate acetylcholine receptors bind & form immune complexes at NM junction

Question 18

What is the diagnostic method for myasthenia gravis?

Answer 18

Electrodiagnostic testing, positive response to anti-cholinesterase therapy & detection of circulating anti-acetylcholine receptor antibodies.

Question 19

Malignant hyperthermia mechanism

Answer 19

defective ryanodine receptor causes a calcium release from sarcoplasmic reticulum.

Question 20

MH pathogenesis

Answer 20

prolonged myofiber contraction & muscle rigidity –> tachycardia, metabolic acidosis & hyperthermia (life threatening)

Question 21

domestic animal species affected by malignant hyperthermia

Answer 21

humans, pigs, horses & dogs

Question 22

Splayleg (condition with corresponding lesion)

Answer 22

congenital muscle condition of piglets and corresponding histopathologic lesion is myofibrillar hypoplasia.

Question 23

Compartment pathogenesis

Answer 23

increase muscle contraction causes increased muscle diameter & pressure

• -> venous outflow collapse, continuous arterial blood supply that causes muscle metabolite accumulation and increases interstitial water
• -> exacerbates intramuscular pressure & blood flow stops causing ischemic necrosis of muscle (worsens in 1-4 hr.)

Question 24

Compartment disease example

Answer 24

pectoral muscles in turkeys and chickens

Question 25

Nutritional myopathy- gross changes

Answer 25

muscle pallor, pale streaking affecting weight bearing muscles (though, shoulder, intercostal muscles, diaphragm & tongue)

Question 26

What type of histologic change occurs with nutritional myopathy?

Answer 26

polyphasic myofiber necrosis

Question 27

What is an underlying cause of equine exertional rhabdomyolysis?

Answer 27

equine polysaccharide storage myopathy

Question 28

What are potential effects of widespread rhabdomyolysis on the kidney?

Answer 28

myoglobininuric nephrosis & renal failure

Question 29

Ionophore effect on muscle

Answer 29

acute monophasic myofiber necrosis (affect skeletal & cardiac m.), once cardiac muscle is damaged it is replaced with fibrosis

Question 30

Senna spp. effect on muscle

Answer 30

acute monophasic myofiber necrosis (skeletal muscle)

Question 31

Gossypol effect on muscle

Answer 31

acute segmental myofiber necrosis ( skeletal & myocardium) + hepatotoxic

Question 32

What are different types of immune-meditated myositis in dogs?

Answer 32

Masticatory myositis
Polymyositis
Bilateral extra-ocular muscle myositis

Question 33

How do you diagnose immune mediated myositis in dogs?

Answer 33

distribution of affected muscles
histopathology
detection of serum type 2M antibodies (masticatory myositis)

Question 34

What are different bacterial agents of clostridial myositis?

Answer 34

a. Blackleg: C. chauvoei
b. Malignant edema: C. speticum
c. Gas gangrene: C. perfringes
d. Swelled head (sheep): C. novyi

Question 35

Gross changes observed with black leg?

Answer 35

i. Muscle is dark red/black, emphysematous & smell like rancid butter
ii. Fibrinous/ fibrohemorrhagic pleuritis & pericarditis

Question 36

What is the best diagnostic method for detecting black leg?

Answer 36

fluorescent antibody testing (hard to culture)

Question 37

What is a benign tumor of striated myofiber?

Answer 37

rhabdomyoma

Question 38

What is malignant neoplasm of myofiber?

Answer 38

Rhabdomyosarcoma

Question 39

List 5 primary muscle tumors of non- muscle origin

Answer 39

soft tissue sarcomas, HAS, LSA, granular cell tumor & infiltrative lipoma