Muscle Diseases

Question 1

What are the symptoms of Equine Rhabdomyolysis Syndrome and why do these symptoms occur?

Answer 1

muscle cramping/ pain that occurs usually during or following exercise due to the breakdown of striated muscle fibres at rest

Question 2

What is Equine Rhabdomyolysis Syndrome also known as ?

Answer 2

Monday Morning disease

Question 3

Does Equine Rhabdomyolysis Syndrome need treating?

Answer 3

If acute- maybe if an emergency but can self resolve
Investigate cause if episodes are recurring

Question 4

What may we see in the blood of a horse with Equine Rhabdomyolysis Syndrome and why?

Answer 4

Increased creatine kinase and aspartamino transferase (AST)- these enzymes are associated with normal muscle function, when muscles get damaged they’re released into the extracellular space into circulation

Question 5

In horses with Equine Rhabdomyolysis Syndrome we see dark reddish tinged urine, why?
How do we differentiate this from bloody urine?

Answer 5

Due to high protein content due to muscle breakdown- to differentiate this from bloody urine we just spin the sample and observe if any sediments lay in the bottom- if they do then these are RBC’s

Question 6

A horse has increased AST but no increase in Creatine Kinase, what does this suggest?

Answer 6

Hepatic disease- BOTH CK and AST need to be high to indicate muscle breakdown

Question 7

How do we treat Acute Exertional Equine Rhabdomyolysis Syndrome?

Answer 7

Analgesics - Opioids preferred
IV or oral fluids to support kidney processing the extra protein

Question 8

What causes ACQUIRED Equine Rhabdomyolysis?

Answer 8

Overexertion e.g. muscle overlengthening, metabolic exhaustion (no glycogen in the muscle)
Electrolyte imbalance
Infectious causes

Question 9

What can cause INHERITED Equine Rhabdomyolysis?

Answer 9

Defective calcium regulation (occurs in Thoroughbreds in the USA)
Polysaccharide storage myopathy

Question 10

How do we prevent Recurrent Equine Rhabdomyolysis (caused by defective calcium regulation)?

Answer 10

Oral dantrolene- a calcium release channel blocker- give before exercise
[careful not to give too much- still need to release some calcium lol]

Question 11

What causes Polysaccharide storage myopathy?

Answer 11

Missense mutation in glycogen synthase (the enzyme responsible for breaking down glycogen branches/ cross links) causing increased activity in skeletal muscle leading to muscle atrophy/ weakness

Question 12

How would we diagnose Polysaccharide storage myopathy? (2)

Answer 12

DNA test for the mutation by submitting blood/ hair pluck
Muscle Biopsy shows accumulation of glycogen in cells

Question 13

How do we manage Polysaccharide storage myopathy?

Answer 13

High Fat, Low carb diet (fat used for energy- less glycogen breakdown)

Question 14

What is Coccygeal Muscle Injury caused by?
How is it treated?

Answer 14

Usually occurs in working breeds after lots of swimming, exercise, cold
Treat with NSAIDs and rest

Question 15

What are the three locations of Ion Channelopathies that cause muscle disease?

Answer 15

Sodium pump
Ryanodine Receptor
Calcium ATPase pump

Question 16

Give an example of a pathology in the Sarcolemmal sodium pump that would cause muscle disease?

Answer 16

Hyperkalaemic Periodic Paralysis- sodium channel stays open causing sodium to rush in > membrane depolarises leading to contraction & then paralysis

Question 17

Give an example of a pathology in the Ryanodine Receptor that causes muscle disease?

Answer 17

Malignant Hyperthermia happens when animals are given dissociative anaesthetics, the drugs induce an opening of the Calcium receptor so calcium flows out

Question 18

Give an example of a pathology in the Calcium ATPase receptor that causes muscle disease?

Answer 18

Congenital Pseudomyotonia- impairs the relaxation of skeletal muscles because calcium cannot go back into the sarcoplasmic reticulum after contraction

Question 19

How do cell signalling defects effect the muscles?
Give an example.

Answer 19

Mutations in the expression of Myostatin which is the protein that restricts excessive muscle growth can cause excessive muscles e.g. Belgian Blue cows, Bully racing whippets

Question 20

What is Fibrotic Myopathy and what causes it?

Answer 20

Abnormal scar tissue forming in the muscle ()most commonly the hamstring) - caused by muscle tear, IM injections

Question 21

What is the tell tale sign of Fibrotic Myopathy in horses?

Answer 21

Characteristic gait- foot slaps on the ground as the fibrous tissue in the muscle acts like a bungee chord

Question 22

What pathology is associated with lipid accumulation in a muscle biopsy and what causes it?

Answer 22

Atypical Myopathy- mitochondria poorly metabolising fatty acids OR ingestion of plant toxin (Hypoglycin A) found in elder or sycamore trees

Question 23

How do muscular dystrophies cause muscle disease?

Answer 23

Proteins known as Dystrophin associated glycoprotein complexes line the muscle fibres- patients with muscular dystrophies have an out of frame deletion of this protein that causes it to lose function

Question 24

Theoretically how could we treat Duchenne Muscular Dystrophy with gene editing?

Answer 24

Use CRISPR to cut and remove so that the exons that had the mutation fit together and become functional again