Muscle Disease

Question 1

How do we diagnose muscle dz?

Answer 1

• CS
• enzymes
• EMG
• muscle biopsy
• exercise challenge test

Question 2

Describe AST enzyme and it’s use:

• is it muscle specific?
• how long does it take to see/leave?

Answer 2

• NOT muscle specific
• increases slowly (12-24h)
• stays elevated longer (2+ weeks)

Question 3

Describe CK enzyme:

• is it muscle specific?
• how long does it take to see/leave?

Answer 3

• YES, muscle specific
• very sensitive
• reflects muscle damage
• peak around 6-8h
• decreases within 3 days

Question 4

What will the CK value look like with:

1. Recumbency with colic
2. Venipuncture
3. Rhabdomyolysis

Answer 4

1. 500-1,000
2. 300-1,000
3. Tens/hundreds of thousands!

Question 5

Describe the method of obtaining muscle biopsy:

Answer 5

Include unaffected + affected muscle

6mm biopsy

Question 6

Exercise challenge test:

• method
• normal values
• increases

Answer 6

• 15-30min of light exercise
• normally won’t see any CK elevations
• 5x increase or more = rhabdomyolysis

Question 7

What is the signalment for Hyperkalemic Periodic Paralysis

Answer 7

Quarter horses

Impressive-line horses

Question 8

CS for HyPP:

Answer 8

• variable!

- intermittent signs by 2-3yo and normal btwn episodes

Question 9

HyPP episode triggers:

Answer 9

Stress
Sudden cold
Transportation
Sudden diet changes
Surgery/anesthetic recovery

Question 10

What are the CS associated with HyPP?

Answer 10

Prolapse of 3rd eyelid
Sweating
Muscle fasiculations
Cramping

• episodes can last min-hrs*
• some young horses that are HOMOZYGOUS can get upper resp muscle paralysis and resp stridor*

Question 11

T/F: HyPP is autosomal recessive inheritance

Answer 11

False!

Autosomal DOMINANT

Question 12

What [in terms of electrolytes] is abnormal in HyPP?

Answer 12

Abnormal Na channels

Hyperkalemia

Question 13

Why are the Na channels abnormal? What is wrong with them?

Answer 13

Resting potential is closer to firing

Na channels remain open

Question 14

T/F: Hyperkalemia in HyPP is only seen during an attack

Answer 14

True!

During attacks, high efflux of K occurs

Question 15

Risk factors for HyPP

Answer 15

• fasting
• general anesthesia
• concurrent illness
• exercise restriction

Question 16

How do we diagnose HyPP?

Answer 16

Gene testing
CS
HyperK in an episode

Question 17

How do you tell patients in renal failure apart from HyPP patients?

Answer 17

Horses in renal failure don’t demonstrate any muscular dysfunctions

otherwise, they both have very high HyperK

Question 18

T/F: As horses age, episode #s increase

Answer 18

False, the episode #s decrease with age

Question 19

DDx for HyPP:

Answer 19

Colic

Seizures

Question 20

How do we treat acute, mild episodes of HyPP?

Answer 20

• light exercise [walking]
• feed some carbs
• feed often

Question 21

How do we treat acute episodes of HyPP with severe hyperkalemia?

Answer 21

1. IV Ca Gluconate [cardioprotection]

2. IV dextrose/insulin to help drive K intracellularly

Question 22

What are some management changes we can try in treating HyPP?

Answer 22

1. Diet: avoid high K feed, feed several times a day
2. Minimize stress
3. Regular exercise

Question 23

T/F: we can feed HyPP horses with alfalfa hay, brome hay, canola oil, soybean oil, sugar, beet molasses

Answer 23

False!! These are all foods high in K.

Instead, we should be feeding them foods low in K: grass hay, grains, sugar beet pulp

Question 24

What is acetazolmide and what does it do for the HyPP horse?

Answer 24

K wasting diuretic BUT since we give lower dose it doesn’t have that diuretic effect.

It stabilizes blood glucose and stimulates insulin secretion

Question 25

What are some possible etiologies for rhabdo?

Answer 25

- inadequate training [pushing them too hard] - alteration of blood supply [post-anesthetic hypotensive episodes] - genetics - underlying muscle abnormalities

Question 26

What does a Type I rhabdo horse look like?

Answer 26

``` Associated with limited exercise 2-4yo nervous filly Weekend rider RER PSSM High grain intake, not exercised regularly ```

Question 27

What does a Type II rhabdomyolysis horse look like?

Answer 27

Endurance horses Overexertion Electrolyte/perfusion disturbances

Question 28

T/F: Mild cases of rhabdo occur AFTER race, poor performance, normal urine color, no muscle pathology, painful/firm hindquarters

Answer 28

True

Question 29

What are some CS of a severely affected rhabdo horse?

Answer 29

- happens DURING exercise - don’t want to move; colic; recumbent - pigmenturia - acute renal failure

Question 30

How do we diagnose rhabdo?

Answer 30

- elevated enzymes [CK over 10k] - muscle biopsy Standard exercise test [shows increase in CK with minimal exertion]

Question 31

How can we treat rhabdo?

Answer 31

- limit exercise [and further muscle damage] - NSAIDs [phenylbutazone] - Muscle relaxant [dantrolene] - fluids [LRS] - vasodilators if normal hydration and not hypotensive [ace] - supportive care

Question 32

T/F: To reduce rhabdo recurrence we can feed them a high carb, low fat, low protein diet

Answer 32

False! - we feed them LOW carb, MOD fat, HIGH protein diet - increase exercise and avoid inactivity periods - dantrolene as prophylactic - acepromazine 30min before exercise

Question 33

What is the signalment for RER horses?

Answer 33

RER = recurrent exertional rhabdomyolysis - young, nervous fillies - autosomal dominant

Question 34

Pathophysiology of RER:

Answer 34

Autosomal dominant, heritable stress-related defect in intracellular Ca regulation

Question 35

T/F: The most reliable diagnostic measure for RER is muscle biopsy.

Answer 35

True. Look for centralized nuclei [vs normal peripheral fiber location]

Question 36

What are some management changes we can make in RER horses? [pretty much same as rhabdo question from before]

Answer 36

- maintain stress-free - dantrolene - exercise them [avoid stall rest] - low carb diet

Question 37

What is PSSM? What is the signalment here?

Answer 37

PSSM = polysaccharide storage myopathy Seen in calm draft horses

Question 38

T/F: Definitive diagnosis of PSSM = glycogen accumulation in cardiac muscle.

Answer 38

False! The glycogen accumulation is in skeletal muscle

Question 39

What can we increase in the diets of PSSM horses to help them?

Answer 39

Increase the fat

Question 40

What is the signalment for anesthetic-related rhabdo?

Answer 40

Muscle mass and hypotension!!!

Question 41

How do we treat anesthetic rhabdo?

Answer 41

Just like exertional rhabdo! - NSAIDs - fluids - dantrolene - low carbs, mod fat, high protein - exercise but only once CK is normal

Question 42

T/F: one major CS of anesthetic rhabdo is prolonged/difficult anesthetic recovery

Answer 42

True!