Disorders of the Muscles

Question 1

What are some clinical signs of muscle disorders?

Answer 1

Tying up or Rhabdomyolysis - stiffness, cramping, reluctance to move, muscle pain and sweating

Muscle atrophy - decrease muscle mass

Muscle Weakness - reluctance to move, hard to get up, stumbling, dragging toes

Muscle fasciculations
Pigmenturia
Exercise Intolerance
Abnormal gait or lameness

Question 2

What is rhabdomyolysis?

Answer 2

Pathway to cell death
-Too much ca in muscles
-Mitochondria sequester ca

Question 3

What is muscle atrophy?

Answer 3

Overt cell death, death of type 1 and 2 (neruogenic) or just 2 myogenic

Question 4

What are muscle fasiculations?

Answer 4

-Abnormal recruitment of nerves
-Irritation nerve root, electrolyte issue, weakness of spinal cord, fatigue, anxiety or shivering
HYPP

Question 5

What are some key things to ask about when approaching muscle disease?

Answer 5

Is it primary or secondary?
Focal or generalized?
Exercise or not?
Rhabdomyolysis
Associated with - pain, atrophy, weakness, electrical conductivity or exercise intolerance

Question 6

What are some forms of exertional myopathies?

Answer 6

Sporadic Exertional Rhabdomyolysis - intermittent increased CK never happened before - dietary or over exertion

Chronic Exertional Rhabdomyolysis - repeated ER and increased Ck - Malignant Hyperthermia, Reccurent Exteritonal , PSSM, MFM

Chronic exertional myopathy - stiff and reluctance but no CK change - PSSM2, myofribillar myopahty

Question 7

What are some forms of Non exertional myopathies?

Answer 7

Metabolic, nutritional (VE and SE), Inflammatory (Immune mediated), Infectious (S. Equi, Clostridum, viral), toxic (ionophore or plant), traumatic, muscle atrophy and muscle fasiculations

Question 8

What are some critical history questions related to muscle disorders?

Answer 8

Exercise associated, regimen, change in tolerance? Change in diet, supplements, pasture? Performance?

Onset, progression signs, frequency, severity, curation, recent changes

Question 9

What should you look for on Physical Exam?

Answer 9

Muscle mass, symmetry, stance, behavior

Muscle palpation heat to tail, flexion and extension and percussion

Question 10

What should you watch for on a moving exam?

Answer 10

Lameness, pain, asymmetry, decreased ROM, stiffness, cramping

Question 11

What would you investigate on bloodwork?

Answer 11

Creatine Kinase, AST, serum CK, electrolytes, renal parameters and urine, may want to check VE and Se

Question 12

What is creatine kinase specific for and how do you know when it is not good?

Answer 12

Skeletal and cardiac muscle damage
-Peak at 4-6 hour, return at 48hr, >4000 u/L - tell acute damage

Question 13

What is AST specific for and how do you know there is an issue?

Answer 13

Not specific - muscle, liver and rbcs
peak 24 hours, normal in weeks, tell you chronic

Question 14

How do you perform the CK exercise test?

Answer 14

Take blood before, exercise and take 4-6 hours later and compare
-Need 3x increase to mean something

Question 15

What electrolytes may we be concerned with if we see muscle fasiculations?

Answer 15

NA, K, CA, CL and P
Hypocalcemia

Question 16

What should we look at to rule out renal?

Answer 16

BUN and Creatine, Myoglobinuria

Question 17

What is critical to remember when sampling vitamin E?

Answer 17

Can be serum or plasma, chilled of frozen but must be protected from light

Question 18

What breeds should be genetic tested?

Answer 18

Quarter horses, draft horses and ponies

Question 19

Where should you take a muscle biopsy for each of the following suspicions?
-Exertional rhabdomyolysis and PSSM:
-Immune mediated myositis:
-Muscle atrophy:

Answer 19

-Exertional rhabdomyolysis and PSSM: semimebranous, middle gluteal
-Immune mediated myositis: glutal or lumbar
-Muscle atrophy: sacrocaudalis dorsalis

Question 20

Does a biopsy help with muscle fasiculations?

Answer 20

no

Question 21

What can a muscle biopsy help with?

Answer 21

Weakness, atrophy, rhabdomyolsis, exercise intolerance

Question 22

What does PSSM stand for?

Answer 22

Polysaccharide Storage Myopathy

Question 23

What is type 1 PSSM caused by?

Answer 23

Mutation in Glycogen Synthase Gene (GSY1)
-increase glucose synthase activity increase glycogen concentration in muscle and disrupts metabolism

Question 24

What is type 2 PSSM caused by?

Answer 24

We don’t know but they don’t have a mutation in GSY1
-Can see on histo though (Amylase sensitive or resisitant

Question 25

How do you treat PSSM?

Answer 25

Stall rest <48 hr, pasture, relieve anxiety, fluids and electrolytes, NSAID, water, hay no grain

Question 26

How do you prevent PSSM?

Answer 26

Daily exercise, gradual return to exercise, daily routine, minimize stress, dietary management (decrease starch)