Muscle

Question 1

What do all muscle diseases result in?

Answer 1

1. Changes in conductivity
2. Damage to muscle tissue
3. Muscle atrophy

Question 2

What do we use to measure rhabdomyolysis severity?

Answer 2

CK values

Short half life so only useful soon after muscle damage has occurred or to track muscle damage effects

Question 3

What are the two types of muscle atrophy?

Answer 3

Neurogenic or myogenic

Aka no longer innervated or no longer paying attention to innervation

Question 4

What is rhabdomyolysis?

Answer 4

Disintegration or dissolution of muscle tissues

aka muscle necrosis

Question 5

What is myositis?

Answer 5

Inflammation of voluntary muscle tissues

Question 6

What is HYPP?

Answer 6

Aka Impressive Disease

Homozygous recessive genetic disease causing bigger muscles that are closer to firing potential at rest which predisposes to random firing

Question 7

What kind of horses typically have HYPP?

Answer 7

Quarter horse and quarter horse mixes

Theorized descendants of Impressive who is thought to have started the disease with a heritable point mutation

Question 8

What are the clinical signs of HYPP?

Answer 8

Odd behavior, fasiculations, recumbency, acute death associated with hyperkalemia

Question 9

What can HYPP episodes be triggered by?

Answer 9

• Stress
• Sudden cold exposure
• Transportation
• Sudden dietary changes
• Recovery from anesthesia/surgery

Question 10

What are HYPP episodes typically NOT triggered by?

Answer 10

Exercise- if signs are seen only post exercise look for other causes

May be associated with increased sympathetic tone which protects from episodes

Question 11

How do you diagnose HYPP?

Answer 11

Genetic testing- UCLA
Potassium challenge test- used more in research

NOT CK levels- no muscle damage in minor episodes

Question 12

How do you treat HYPP?

Answer 12

Breeding management for prevention best strategy

During episodes- IV Ca gluconate (brings up firing threshold), Insulin or dextrose (drives potassium intracellularly)

Acetazolamine- potassium wasting diuretic to minimize episodes

Question 13

T/F: Some horses will “out-grow” HYPP episodes and clinical signs will diminish.

Answer 13

True- still should not be used for breeding

Question 14

How do you control HYPP?

Answer 14

• Avoid high potassium feeds (alfalfa), feed in smaller frequent meals, avoid fasting
• Regular episodes
• Avoid stress

Question 15

What is the hallmark of exertional myopathies?

Answer 15

Rhabdomyolysis

Question 16

What are other names for exertional myopathies?

Answer 16

Monday Morning Disease, Tying-Up, Set-Fast, Chronic intermittent Rhabdomyolysis, paralytic myoglobinuria, exercise-associated myositis

Question 17

What are some specific conditions associated with exertional myopathies?

Answer 17

• Polysaccharide storage myopathy (quarter and draft horses)

- Recurrent exertional rhabdomyolysis (thoroughbreds)

Question 18

What are some causes of exertional myopathies?

Answer 18

Dietary, overexertion, genetic/inherited conditions, circulatory issues

Question 19

What is monday morning disease?

Answer 19

Horse that was fed grain all week while it was working and then fed grain on it’s off day and then had issues on the next day

Mostly seen in Draft horses

Question 20

What are some genetic/inherited errors in metabolism resulting in exertional myopathies?

Answer 20

PSSM and RER in belgians, quarter horses, thoroughbreds

Question 21

What are some circulatory disorders resulting in exertional myopathies?

Answer 21

Post anesthetic myopathies and compartmental syndrome

Question 22

What are some metabolic/endocrine issues that can lead to exertional myopathy?

Answer 22

• Electrolyte imbalances
• Abnormal thyroid function
• Hormonal imbalances

Question 23

What is the simplest cause of exertional myopathy?

Answer 23

Exertion…. they’re being trained too hard

Question 24

What kind of circulatory issues do we see with exertional myopathies?

Answer 24

 Compromised perfusion of the muscles 
 Increasingly acidic environment
 Muscle necrosis, breakdown
 Hypoxia
 Swelling which further contributes to reduced perfusion and ongoing hypoxemic state of muscles

Question 25

What is type I exertional myopathy present with?

Answer 25

Associated with limited exercise- not overworked
 2-4 year old “nervous” or “high-strung” filly (most end up being RER horses)
 Weekend rider – used of unfit horse for exercise out of their ability
 Wont develop really bad CS

Question 26

What is type II exertional myopathy present with?

Answer 26

Associated with protracted exercise
 Endurance horse in high competition
• In generally very fit but can be overworked
• If it “ties up” it does not mean the horse will do it again in the future—just don’t overwork it
 Electrolyte and circulatory causes

Question 27

What are some clinical sighs of exertional myopathy?

Answer 27

Fasciulations, sweating, muscle swelling, tachycardia and tachypnea, hardened painful muscles

Variable degrees of pigmenturia and myogolbinuria depending on severity of episode

Question 28

What is the difference in muscle presentation between exertional myopathies and HYPP episodes?

Answer 28

HYPP will not have hardened painful muscles

Question 29

What are the CK values that are useful for determining cause of increase?

Answer 29

CK – 150-400 IU/L = normal tells about acute, on-going damage
980 IU/L: Not tying up – more compatible with blood draws that you are “fishing” in
2000 IU/L: Colic-y horses moving around/throwing themselves
20,000 IU/L: Rhabdomyolysis occurs at 10,000 but you still need to look at timing

Question 30

What are common PE/lab findings with an acute episode of exertional myopathy?

Answer 30

PE: hard, swollen, painful muscles
Chem: May see electrolyte imbalances and acidosis

Question 31

What is important to look at in mild or recurrent episodes of exertional myopathy?

Answer 31

Urinary fractional excretion of electrolytes
Exercise challenge test
Vit E/Sel evaluation
Muscle biopsies

Question 32

What is the goal with an exercise challenge test?

Answer 32

Produce CK elevation without clinical signs to show damage to muscle with little work- indicates a genetic issue

Question 33

When are muscle biopsies most helpful in diagnosing?

Answer 33

Genetic inherited disorders with recurrent episodes

Question 34

What is the goal of long term management of exertional myopathies?

Answer 34

Prevent whatever set off the episode to begin with

Question 35

How do you treat an episode of exertional myopathy?

Answer 35

Limit the muscle damage nby limiting movement
Restore normal electolyte balance
Relieve pain and inflammation (phenylbutazone)
Improve renal perfusion

Question 36

T/F: Excessive/prolonged myoglobinuria can cause acute renal failure.

Answer 36

True- one of the only causes of renal failure in the horse and typically cause of death in horses with exertional myopathies

Question 37

How can you change the diet of a horse with exertional myopathies to help prevent episodes?

Answer 37

High fat diet- rice bran and high oil content (18-22%)

Question 38

How does dietary management help horses with PSSM and RER?

Answer 38

PSSM- decrease in muscle cell glycogen accumulation

RER- calmer animals and reduces CK elevation with exercise, lower resting HR and lower PCV

Question 39

What is the most important aspect of post-anesthetic myopathies?

Answer 39

Muscle mass and length of surgery

Draft horses most prone to it

Question 40

What can be done during surgery to help prevent post-anesthetic myopathies?

Answer 40

Maintaining MAP >60

Question 41

What is RER?

Answer 41

o Autosomal dominant Inherited disorder of Thoroughbreds – 65% are fillies
o Frequency 2 years

Question 42

What is PSSM?

Answer 42

o Autosomal dominant: Glycogen synthase 1 gene point mutation
o Increased clearance of glucose in circulation
o Accumulation of glycogen and abnormal polysaccharides in muscle cells
o Identified: QTR and Drafts but also seen in American paint horses, appaloosas, and warmbloods