congenital muscle abnormalities, muscle atrophy

Question 1

What are the 3 main congenital muscle abnormalities?

Answer 1

1. Muscle dystrophy
2. Myotonia
3. Equine Polysaccharide Storage Myopathy (PSSM)

Question 2

What are the 2 morphological features of muscle dystrophy?

Answer 2

1. Muscle degeneration: presents as muscle swelling // edema due to lack of dystrophin (protein that strengthens muscle fibers and protects them from injury as muscles contract and relax) –> –> leakage of cells

followed by

2. Muscle necrosis: muscle shrinks and fibrosis occurs, replacing the edema

Question 3

Stiff gait, decreased exercise intolerance, decrease in muscle mass, loss of motor coordination and megaesophagus are all signs for what congenital muscle abnormality?

Answer 3

Muscle dystrophy

Question 4

Stiff, uncoordinated gait that turns into rigidity and fainting-like signs are signs for what congenital muscle abnormality?

Answer 4

Myotonia: inability of skeletal muscle to relax after contraction (aka hyper-contractility)

Question 5

What is exertional rhabdomyolysis (“tying-up”) in breeds like racing horses?

Answer 5

the breakdown of skeletal muscle (dissolution of striated muscle cells) as a result of over-exercise

Question 6

What is Equine Polysaccharide Storage Myopathy (PSSM)?

Answer 6

Abnormal buildup of muscle glycogen within myocytes due to a defect in the “GYSI” gene that causes abnormal carbohydrate metabolism

Question 7

What are 3 signs of PSSM?

Answer 7

1. exertional rhabdomyolysis
2. stiff/altered gait
3. indications of painful stride

Question 8

Which muscle fibers are anaerobic?

Answer 8

The fast-twitch muscle fibers, Type 2

Question 9

Which muscle fibers are aerobic?

Answer 9

The slow-twitch muscle fibers, Type 1

Question 10

A dog who has asymmetrical muscle atrophy and whose Type 2 muscle fibers are predominantly affected is experiencing this muscle atrophy because of:

Answer 10

Disuse

• casted limb
• severe lameness

Question 11

A starved dog with symmetrical muscle atrophy and whose Type 2 muscle fibers are predominantly affected is experiencing this muscle atrophy because of:

Answer 11

Cachexia – the wasting away of the body due to systemic dz (e.g., neoplasia, etc.). The animal becomes anorexic and its body beings to mobilize muscle protein for energy.

Question 12

What is Roarer’s syndrome?

Answer 12

Unilateral denervation of the left cricoarytenoideus dorsalis (principle abductor m. that widens laryngeal aperture) due to damage to the left recurrent laryngeal nerve, causing rapid muscle atrophy and the loss of Type 1 & 2 muscle fibers.

Question 13

What type of muscle fibers do endocrine diseases like hypothyroidism and hyperadrenocorticism disease predominantly affect in muscle atrophy?

Answer 13

Type 2 (fast-twitch, fatigue-sensitive)

Question 14

What are the differences between physiologic and compensatory muscle hypertrophy?

Answer 14

Physiologic: increased muscle fiber size due to increased physiological work (e.g., exercise conditioning in racing horses)

Compensatory: increased muscle fiber size due to increased work from the lack or absence of other fibers, caused by a partially denervated muscle

Question 15

What are the morphological features of hypertrophic cardiomyopathy, a primary muscle abnormality?

Answer 15

Abnormally thickened left ventricular wall and inter-ventricular septum. Formation of thrombus in the left atrium can lead to a saddle thrombus.