YR3 15 M HO1

Question 1

Muscle Injury - 3 outcomes

Answer 1

Sarcolemma intact > complete regeneration possible / Extensive damage, fibrous tissue fills defect / Severe damage > complete myocyte necrosis, fibrosis fills in gap left in muscle.

Question 2

Muscle Repair - Intact sarcolemma

Answer 2

Macrophages enter and remove debris > satellite cells produce more muscle protein > cells return to sarcolemma surrounding myocyte

Question 3

Muscle damage; gross

Answer 3

Damaged myocytes swell > pushes blood out resulting in a pale appearance to damaged skeletal muscle

Question 4

Muscle Injury - Classification

Answer 4

1)Monofocal 2)Multifocal 3)Monophasic 3)Multiphasic

Question 5

Monofocal

Answer 5

One location within the body e.g. an injection reaction

Question 6

Multifocal

Answer 6

Multiple areas within the body e.g. a toxic process

Question 7

Monophasic

Answer 7

A single episode of necrosis e.g. capture myopathy. All lesions are the same age

Question 8

Multiphasic

Answer 8

Multiple episodes of necrosis e.g. muscular dystrophy. Lesions are different ages within the muscle (evidence of necrosis, repair and regeneration all visible)

Question 9

Altered Myocyte Size - Denervation Atrophy

Answer 9

1 - Rapid w/ marked decrease in myocyte size 2 - More commonly the entire muscle atrophies but partial nerve damage > clusters of atrophic cells 3 - Long nerve degeneration commonly occurs in large breed dogs and horses

Question 10

Explain Roaring in horses

Answer 10

Degeneration of the left recurrent laryngeal nerve > laryngeal muscle paralysis > roaring

Question 11

Altered Myocyte Size - Disuse Atrophy

Answer 11

Less severe than denervation atrophy. Caused by restricted movement in a limb

Question 12

Altered Myocyte Size - Atrophy due to Cachexia

Answer 12

Marked malnutrition or neoplasia. Typically postural muscles less affected

Question 13

Altered Myocyte Size - Hypertrophy Physiologic

Answer 13

Due to exercise

Question 14

Altered Myocyte Size - Hypertrophy Pathologic

Answer 14

Due to loss of contralateral limb. Myocyte hypertrophy due to loss of other myocytes within the muscle. If severe can get muscle splitting

Question 15

Congenital Muscle Disease - Myotonia

Answer 15

Involuntary contraction of a muscle group due to a defect in regulation of ion channels

Question 16

Congenital Muscle Disease - Myotonia; clinical signs

Answer 16

1)Mild to moderate muscle hypertrophy 2)Stiff gait 3)Sudden collapse w/ spontaneous resolution 4)Exercise intolerance

Question 17

Congenital Muscle Disease - Congenital Muscle Hypertrophy

Answer 17

Normal in some cattle breeds e.g. Belgium Blue. Muscle contains reduced adipose

Question 18

Congenital Muscle Disease - Steatosis

Answer 18

Replacement of myocytes w. adipose. Usually incidental finding

Question 19

Congenital Muscle Disease - Muscular Dystrophy

Answer 19

Cytoskeletal protein defect. Rare in dogs and cats except Labradors. Death usually due to heart failure as cardiac myocytes also affected

Question 20

Duchenne Muscular Dystrophy -Human; gross, histo

Answer 20

Pseudohypertrophy of calf muscles due to fat infiltration. Multiphasic necrosis of cardiac muscle

Question 21

Congenital Muscle Disease - Splayleg Pigs/Swimmer Dogs

Answer 21

Animals usually spontaneously recover when older

Question 22

Congenital Muscle Disease - Malignant Hyperthermia; aka, pathogenesis

Answer 22

Porcine Stress Syndrome Triggered by stress or halothane > defect in ryanodine receptor causes uncontrolled sustained contraction > Excessive heat and lactic acid production result in myocyte necrosis > Multifocal monophasic necrosis

Question 23

Congenital Muscle Disease - Malignant Hyperthermia; gross, histo

Answer 23

Gross - ‘Cooked’ appearance Histo - Monophasic acute necrosis

Question 24

Congenital Muscle Disease - Storage Diseases

Answer 24

1 - Most common is polysaccharide myopathy 2 - Most common in draft breed horses 3 - Predisposes to extertional rhabdomyolysis > recurrent episodes of exertional rhabdomyolysis results in fibrosis and associated weakness 4 - Muscle biopsy reveals large quantities of intracellular carbohydrates

Question 25

Environmental & Physical Disease - Extertional Rhabdomyolysis

Answer 25

Horses mainly - Tying up, Monday morning disease, sit-fast, azoturia Stiffness, muscle swelling, pain immediately following exercise > most often involves the gluteals
Myocyte necrosis result in increased serum CK Can get myoglobinemia & myoglobinuric nephrosis

Question 26

Environmental & Physical Disease - Capture Myopathy

Answer 26

Necrosis caused by prolonged muscle activity > Animals can die quickly due to metabolic acidosis or myoglobinuric nephrosis

Question 27

Environmental & Physical Disease - Trauma

Answer 27

Common in animals > Traumatic muscle necrosis e.g. ‘Downer’ cows