Muscle Pathology (LS)

Question 1

Myofiber responses to injury?

(6)

Answer 1

• Regeneration
• Necrosis
• Atrophy
• Hypertrophy
• Split
• Fiber-Type Conversion

Question 2

Histologic lesions of mm. necrosis?

(3)

Answer 2

• nuclei disappear
• hyalinized sarcoplasm→ eosinophilic, amorphous & homogenous
• may seperate from adajenct viable myofiber

Question 3

What features characterize a regenerating mm. fiber?

Answer 3

• basophilia → increased RNA content
• internal nuclei → rows
• lack of striations
• diameter → smaller than normal

Question 4

Describe mm. fiber regeneration.

(3)

Answer 4

• Satellite cells → myoblasts → myotubes → myofibers
• Requires →intact endomysial framework
• Success→ integrity of sarcolemma determines

(occurs w/in several days for most species)

Question 5

What is Muscle Atrophy?

Answer 5

DECREASED size + HYPERtrophy =

INCREASED muscle fiber size

(NO NEW CELLS)

Question 6

List the 2 Primary Neoplasms of Mm.

Answer 6

• Rhabdomyoma
• Rhabdomyosarcoma

Question 7

What occurs in “Compartment Syndrome”?

Who gets it?

Answer 7

• mm ischemia
• swelling in a nonexpandilble compartment
• Poultry → Deep Pectoral Myopathy → vigorous wing flapping

Question 8

List the 2 causes of Exertional Myopathies.

Answer 8

• Capture myopathy
• Exertional rhabdomyolysis

Question 9

Give some other names for Extertional Rhabdomyolysis.

(6 total)

Answer 9

• Exertional myopathy
• Azoturia
• Setfast
• Black-water
• Monday morning dz.
• Tying up

Question 10

Which bacT causes Myositis in LAs?

Answer 10

Clostridium spp.

Question 11

Give an expamle of a Bacterial Myopathy seen in Equines.

Answer 11

Gas gangrene

AKA

Malignant edema

Question 12

Give an example of Bacterial Myopathy seen in Cattle.

Answer 12

Blackleg

(C. chauvoei)

Question 13

Which nematode can cause INTRAcellular Parasitic Myopathy in Pigs?

Answer 13

Trichinella spiralis

Question 14

Which cestode larvea causes EXTRAcellular Parasitic Myopathy in food animals?

Answer 14

Cysticercus spp.

Question 15

List the 3 Immune-Mediated mm. disorders.

Species seen in?

Answer 15

• Acquired Myasthenia gravis → cat, dog
• Masticatory Myositis→ dog
• Purpura hemorrhagica → horse

Question 16

4 Lesions of Arthrogryposis in cattle & sheep.

Answer 16

• muscular HYPOplasia → decreased size
• 1° lesions in brain/spinal cord
• “crooked limbs”
• rigid joints

Question 17

Cause of Arthrogryposis in Sheep?

Answer 17

in utero toxicosis w/ Parabendazole in 1^st trimester→ fetus/neonate→ CNS lesions→ denervation of skeletal mm.

Question 18

What leads to Congenital Muscular Hyperplasia?

Answer 18

mutation of myostatin

INCREASED # of myofibers → double mm.

Question 19

“Splayleg” or “Spraddle legged” in Pigs is the result of what?

Answer 19

Congenital Myofibrillar HYPOplasia

Question 20

2 Lesions of Congenital Myofibrillar HYPOplasia (splayleg in pigs).

Answer 20

• DECREASED # of myofibers
• atrophic, flabby, pale, wet mm.’s.

Question 21

Pathogensis of Muscular Dystrophy?

Answer 21

degenerative changes→ loss of mm. fibers→ failed attempts to regenerate → REPEATS → mm. replaced by fat & fibrous CT.

Question 22

Muscular Dystrophy is RARELY seen in animals.

List the 3 exceptions (all inherited/still rare).

Answer 22

• Merino sheep
  
  • stiff gait, neuromuscular weakness, exercise intolerance
• K9 X-linked
  
  • dystrophin deficiency in MALE Golden Retrievers
• Heritable Myopathy of Labs (HMLR)
  
  • “bunny hopping”, mm weakness, exercise intolerance, megaesophagus, etc.

Question 23

Which animals get Myotonia (channelopathy)?

Answer 23

• Horses → Thoroughbreds, Standardbreds, Quarterhorses
• Goats
• Dog
• Cat

Question 24

What are the other names for Porcine Malignant Hypertermia?

(4)

Answer 24

• Porcine Stress Syndrome (PSS)
• Pale Soft Exudative (PSE) pork
• “Herztod”
• Black Mm. Necrosis

Question 25

What inhalant anesthetic can trigger **PSS**?

Answer 25

Halothane

Question 26

Pathogensis of **PSS**?

Answer 26

* inherited defect in Ca²⁺ regulation→ uptake, storage & release * Hypermetabolic state

Question 27

What causes **Rigor Mortis**? Progression?

Answer 27

* decreased Ca²⁺ ATPase pump activity (No O₂) → sustained contractions * jaws →trunk →extremities

Question 28

Pathogenesis of **HYPP**?

Answer 28

* Defect in skeletal mm. Na⁺ channels * INCREASED INTRAcellular Na⁺ * INCREASED EXTRAcellular K⁺

Question 29

2 Causes of **HYPP** in horses?

Answer 29

* Hereditary → Impressive bred AQH * Post-anesthetic recumbancy

Question 30

Lesion of **HYPP**?

Answer 30

Pale myofibers w/ vaculoar degeneration

Question 31

**Steatosis** (Lipomatosis) is responsible for ______ \_\_\_\_\_\_.

Answer 31

Excess marbling

Question 32

Pathogenesis of **Steatosis**.

Answer 32

Defective myofiber developement → myofibers replaced w/ fat → no alterations in gross mm. ## Footnote (NOT clinically significant)

Question 33

What is the cause of **Muscular Dystrophy**?

Answer 33

* Abnormal protein → progressive degeneration * Inherited

Question 34

**Monofocal Monophasic** **Necrosis** is due to?

Answer 34

Local trauma

Question 35

**Monofocal Multiphasic** **Necrosis** is due to?

Answer 35

Repeated local traumas

Question 36

**Multifocal Monophasic Necrosis** is due to?

Answer 36

One insult that causes lesions @ multiple sites * single exposure myoctoxins * metabolic disorders

Question 37

**Multifocal Multiphasic Necrosis** is due to?

Answer 37

Ongoing insult that causes lesions in multiple sites. * Nutritional deficiency * Muscular dystrophy

Question 38

Lesions of mm. **Degeneration**? (3) (Reversible if not necrotic)

Answer 38

**_Gross → PALLOR_** * Chalky-white calcification **_Micro:_** * **Zenker's** degeneration appearance→loss of striations

Question 39

4 common mechanisms of **Muscle Necrosis**?

Answer 39

* ATP depletion→ hypoxia * Free radicals * Membrane damage * Mitochondrial damage due to Ca²⁺ influx

Question 40

Pathogenesis of **White Muscle Dz**?

Answer 40

Se/Vit E deficiency → decreased lipid **peroxidation**→ free radicals damage CM → Ca²⁺ influx → segmental necrosis

Question 41

Lesions of **WMD**?

Answer 41

* Hyperesinophilia * loss of mm. striations * calcification

Question 42

3 Causes of **Azoturia**?

Answer 42

* Se deficiency * Electrolyte abnormalities * **Forced exercise after rest & heavy feeding**

Question 43

3 Clinical Signs of **Azoturia**?

Answer 43

* Sudoresis → profuse sweating * Myoglobinuric Nephrosis → dark, black kidneys * Acidosis

Question 44

3 Lesions of **Capture Myopathy**? | (wild animals)

Answer 44

* pronounced acidosis * bilaterally symetrical lesions * pale, swollen, edematous mm's

Question 45

Which 2 species get **HYPOKALEMIA**?

Answer 45

* Cattle * Cats

Question 46

Pathogenesis of **HYPOKALEMIA**?

Answer 46

* Altered mitochondrial fxn → Ischemia → myofiber necrosis * abnormal cardiac conductance

Question 47

**HYPOKALEMIA** in **Cats**?

Answer 47

* Hyperpolarization → 2° excess Na⁺ permeability * _+_ Chronic interstitial nephritis * Neck ventriflexion

Question 48

3 Clincal Signs of **HYPOPHOSPHATEMIA** in **Cattle**? **TQ!!!!!**

Answer 48

* PROFOUND mm. weakness * Neuro signs * Hemolytic anemia

Question 49

4 CS of **HYPERCORTISOLISM**?

Answer 49

* stiff pelvic gait * increased bulk & tone of proximal thigh mm's * Cushingoid psuedomyotoni * denervation atrophy

Question 50

Pathogenesis of **HYPERCORTISOLISM**?

Answer 50

Increased cortisol → **denervation atrophy w/ regeneration** ## Footnote (different than hypothyroidism)

Question 51

Pathogenesis of **Blackleg**?

Answer 51

Ingestion of *C. chauvoei* spores → injury to mm → endotoxin release

Question 52

4 Lesions of **Blackleg**?

Answer 52

* Gas * Rancid odor * **Serohemorrhagic exudate** * **Increased myositis**

Question 53

Cause of **Malignant Edema** (Gas Gangrene) in **horses, pigs & ruminants**?

Answer 53

Introduction of *Clostridium perfringens* via puncture wound

Question 54

2 Lesions of **Malignant Edema**?

Answer 54

* Affected areas are cold * Increased cellulitis

Question 55

Cause of **Eosinophilic Myositis** in **Cattle**? Hallmark lesion?

Answer 55

* Idiopathic Hypersensitivity to **Sarcocystis** infection * **Green** color to mm.

Question 56

Cause of **Masticatory MM. Myositis** in **Dogs** (GSD)? Lesions?

Answer 56

* **Antibodies to Type IIC myofibers** * a form of **acute eosinophilic myositis** * **Swollen fibers infiltrated w/ eosinophils**

Question 57

3 Lesions of **Polymyositis** in **Dogs**?

Answer 57

* **Lymphoplasmacytic inflammation** → immune mediated * megaesophagus * Lymphocytes + plasma cell infiltration

Question 58

Cause of **Purpura Hemorrhagica** in **Horses**? 3 Lesions?

Answer 58

* Immune complexes due to Strangles infections * Leukoclastic vasculitis * Petechiae * _+_ glomerulonephritis

Question 59

Lesion of **Actinobacillosis** (Wooden Tongue) in **Cattle**?

Answer 59

* lesions is hard granuloma of Bacilliosis (no pus)

Question 60

Lesion of **Actinomycosis** (Lumpy Jaw) in **Cattle**?

Answer 60

Granulomas w/ **caseous-suppurative centers** (pussy) LOL!!!!

Question 61

Lesion of **Rhabdomyoma**?

Answer 61

Large, pedunculated mass ## Footnote (originates in heart 66% of time)

Question 62

Lesions of **Rhabdomyosarcoma**?

Answer 62

* Distant Metastasis * Poorly encapsulated, spherical nodules * Pink/grey tissue

Question 63

What is the name for "**Grape-like" tumors** found in **urinary trigone** of **large breed dogs**?

Answer 63

Botryoid Rhabdomyosarcoma

Question 64

Cause of **Congenital Myasthenia Gravis**?

Answer 64

Low # of ACh receptors Lack of ACh receptors

Question 65

Cause of **Acquired Myasthenia Gravis**?

Answer 65

IgG to ACh receptors (auto-immune)

Question 66

3 Lesions of **Acquired Myasthenia Gravis**?

Answer 66

* **2° megaesophagus** * 2° dysphagia * 2° thymoma

Question 67

TX **Acquired Myasthenia Gravis**?

Answer 67

Anticholinesterase drugs → **Neostigmine**

Question 68

Pathogenesis of **Botulism toxicity**? Who's most sensitive?

Answer 68

* Endotoxins prevent ACh release → flaccid paralysis * Horses \> Rumi's

Question 69

2 Causes of **Perosis of Birds**?

Answer 69

* displacement of "gastrocneumius" * Mn or Choline deficiency

Question 70

Lesion of **Monensin** (Ionophore)?

Answer 70

* Pale, ill defined streaks in skeletal & cardiac mm.