Pathology of Skeletal Muscle Pt 2

Question 1

What is Arthrogryposis?

Answer 1

Arthrogryposis: Congenital condition in aborted fetuses (cattle & sheep)and stillborns characterized by rigid joints and limbs in abnormal grotesque positions.

Question 2

What pathology is seen in this image? What is it associated with/ the cause?

Answer 2

Arthrogryposis: Congenital condition in aborted fetuses (cattle & sheep)and stillborns characterized by rigid joints and limbs in abnormal grotesque positions.

• Unclear etiology but usually associated with developmental abnormalities of the nervous system (e.g.: spina bifida, syringomyelia etc.,).
• Lack of innervation(denervation), leading to muscle hypoplasia, is the most common cause.
• Maybe the result of ingestion of toxins, or in-utero viral infections ( akabane disease, cache valley fever and blue tongue cause clusters of arthrogryposis in cattle and sheep.

Question 3

What is muscle dystrophy? What are the animal models for Duchenne’s muscular dystrophy?

Answer 3

Muscle Dystrophy: Genetically determined, progressive degenerative disease of muscle. Regenerative attempts are inadequate or absent. Described in multiple species.
• The mouse, dog & cat are animal models for Duchenne’s muscular dystrophy

Question 4

What is the cause of Duchenne’s muscular dystrophy?

Answer 4

affected animals and people lack dystrophin, a cytoskeletal protein that strengthens muscle and protects it from injury.

Question 5

What is the cause of the pathology in this image?

Answer 5

An X-linked dystrophin gene defect has been identified in Golden Retrievers. Telegraph.co.uk
Similar disorders have been diagnosed in other breeds including Irish Terriers, Samoyeds, Labrador Retrievers, Rottweilers, Dalmatians etc.) Muscle degeneration/ necrosis and fibrosis lead to progressive clinical disability in young male dogs. Dogs are considered the best animal model for human muscular dystrophy. The heart and esophagus are also involved (progressive cardiomyopathy and megaesophagus). Note muscle wasting and a characteristic outward rotation (splaying) of fore limbs (image). Death may be the result of aspiration pneumonia or cardio-respiratory failure.

Question 6

What is the characteristics of x linked dystrophin gene defect and potential causes of death?

Answer 6

Note muscle wasting and a characteristic outward rotation (splaying) of fore limbs (image). Death may be the result of aspiration pneumonia or cardio-respiratory failure.

Question 7

What is Equine Polysaccharide Storage Myopathy (EPSSM)? What is the suspected cause?

Answer 7

Inherited disease reported mainly in QH, Arabian horses, Morgans, Ponies and draft-related breeds. Some animals are asymptomatic, others exhibit gate abnormalities (hind limb lameness) and reduced muscle mass. Microscopically there is accumulation of PAS positive material (polysaccharides) in skeletal muscle associated with degeneration/ necrosis of type II fibers.
- An underlying carbohydrate metabolic disorder is suspected.

Question 8

What is Porcine stress syndrome (porcine malignant hyperthermia) ? What are the signs? What pigs are more susceptible?

Answer 8

Inherited disorder of domestic pigs (Pietrain, Yorkshire, Duroc, Landrace etc.,) – single point mutation in the skeletal muscle ryanodine receptor gene (ryr1).

• Hypermetabolic syndrome characterized by dyspnea, muscle rigidity and convulsions, hyperthermia, lactic acidosis, hyperkalemia, cardiovascular collapse and death.
• Heavy-muscle pigs are more susceptible to clinical disease,

Question 9

What is the pathogenesis of Porcine Stress Syndrome (porcine malignant hyperthermia)?

Answer 9

Pathogenesis related to the uptake, storage and release of Ca ions -> the ryanodine receptor is a Ca release channel -> uncontrolled Ca release leads to excessive muscle contraction and heat production (hyperthermia).

Question 10

What is going on in this image? What are characteristics of this pathology? What causes extramuscular lesions in pigs that have passed away?

Answer 10

Porcine Stress Syndrome (PSS) – Pale swollen and “wet” muscles (longissimus dorsis)

Extramuscular lesions in pigs that died of PSS are those of acute heart failure: pulmonary edema and congestion, hydropericardium, hydrothorax and hepatic congestion.

Question 11

What is the cause of White muscle disease?

Answer 11

The result of Vit E/ Se deficiency

• Primarily a disease of young animals
• Usually affects the rapidly growing and best nourished animals in the herd/ flock

Question 12

What is the pathogenesis of white muscle disease? Who is this most common in?

Answer 12

Pathogenesis: Oxydative damage (lipoperoxydation of cell membranes) due to deficiency in oxygen-radical scavengers: Vit E and selenium- containing enzymes like glutathione peroxidase/ reductase.

In addition to skeletal muscle the heart may also be affected

• Most common in sheep, cattle and pigs, In cattle primarily affects calves 1-6 months of age
• In pigs can co-exist with other Vit E/ Selenium syndromes (hepatosis dietetica, mulberry heart disease).

Question 13

What are the signs / symptoms of white muscle disease?

Answer 13

Stiffness and dyspnea are common clinical signs.

• Intercostal muscles and diaphragm (type I fibers) are often affected even when there is little involvement of other skeletal muscles.
• In cases in which skeletal muscle lesions predominate they are most severe in muscles of the thigh and shoulders.
• In nursing calves, the tongue and neck muscles are often affected (more active muscles -> Increase production of free radicals).

Question 14

What can be seen in this image?

Answer 14

White muscle disease

Question 15

What is occuring to the muscle in this histological slide?

Answer 15

Calcification, nutritional myopathy

Question 16

What is occuring in this image?

Answer 16

White muscle disease, chalky/ gritty cardic muscle.

Question 17

What is an exertional myopathy?

Answer 17

Group of diseases characterized by muscle damage initiated by muscle activity (exercise, stress) in which the underlying cause is unknown or poorly understood.

• Such activity may be intensive or exhaustive but in susceptible individuals exertional myopathy may occur with only minimal exercise

Question 18

What are examples of exertional myopathies?

Answer 18

Hyperkalemic periodic paralysis (HYPP)

Exertional Rhabdomyolysis

Greyhound & racing sled dog myopathy

Capture Myopathy

Compartment Syndrome

Question 19

What is Hyperkalemic periodic paralysis (HYPP)?

Answer 19

Inherited condition.
Affected horses are descendants of a famous Quarter Horse stallion named Impressive. Well defined muscle groups rewarded in halter competitions. Underlying defect: alteration in muscle sodium channel (leading to release of potassium in the bloodstream and extracellular space -> transient muscle spasms (myotonia), could lead to flaccid paralysis and even death.

Question 20

What are other names of Exertional Rhabdomyolysis?

Answer 20

azoturia, tying up, paralytic myoglobinuria, Monday morning disease

Question 21

Who is most susceptible for Equine Exertional Rhabdomyolysis? What are causes, what are other underlying metabolic myopathies that are common in affected horses?

Answer 21

Heavy horse breeds are more susceptible to severe disease

• Unclear etiology but appears to be multifactorial (overexertion, exhaustion, dietary imbalances including electrolyte depletion and low Se/ Vit E levels may be implicated).
• Underlying metabolic myopathies like equine polysaccharide storage myopathy (EPSSM) seem common in affected horses.
• Strong evidence for a genetic predisposition

Question 22

Exertional Rhabdomyolysis: What muscles are most commonly affected? What lab values are elevated? What is the most common cause of death in affected animals.

Answer 22

Gluteal, femoral and lumbar muscles are commonly affected: swollen and rigid (board-like consistency)

• Elevated levels of CK and AST (Aspartate Aminotransferase)
• Myoglobinuric nephrosis is the most common cause of death

Question 23

What is capture myopathy?

Answer 23

Acute, often fatal disease seen most often in wild mammals and birds following strenuous physical activity (exertion) during capture or transport.
• Lesions: Muscle degeneration-necrosis- hemorrhage; occasional ruptured tendon; myoglobinuric nephrosis may occur.

Question 24

What is compartment syndrome? Who does it occur in ? What is the primary animal seen in veterinary medicine who this syndrome is seen in?

Answer 24

Ischemic damage that occurs in muscles surrounded by heavy aponeurosis (connective tissue sheaths) or by bone and sheaths (non-expandable compartments) when subjected to moderately vigorous contractions.
• Occurs in well-conditioned athletes
• In veterinary medicine is primarily observed in the supracoracoideus muscles poultry (chickens, turkeys) following brief but vigorous flapping of the wings (deep pectoral myopathy).

Question 25

What is seen in this image?

Answer 25

Deep Pectoral myopathy, supermarket chicken, UK

Question 26

What is occuring in this image of a chickens muscle?

Answer 26

Injection site necrosis

Question 27

What is downers syndrome? What animal is this most common in?

Answer 27

Downer syndrome: Represents ischemic necrosis of ventral and limb muscles following prolonged recumbency.

• The weight of the body on a limb tucked under the body for a long period of time results in increased pressure on the vasculature -> edema -> more pressure -> ischemic necrosis.

• Large animals in good body condition are more susceptible.

• Most common in cows because of their weight, muscle mass and susceptibility to diseases in which paresis is frequent.

Question 28

What is the cause of downers syndrome?

Answer 28

The weight of the body on a limb tucked under the body for a long period of time results in increased pressure on the vasculature -> edema -> more pressure -> ischemic necrosis.

Question 29

What is the cause of this muscle lesion in a cow?

Answer 29

Downers syndrome

Question 30

What is occuring in this image of a cows thigh muscle?

Answer 30

Downer cow – Ischemic necrosis of thigh muscles.

Question 31

What is Equine Post-anesthetic myopathy? What is crush syndrome?

Answer 31

Equine Post-anesthetic myopathy: Occurs in 3- 6% of cases in which general anesthesia is used -> different degrees of severity.
• Crush syndrome: Caused by acute trauma. Pathogenesis and lesions similar to Downer syndrome.

Question 32

What are other potential traumatic muscle injuries?

Answer 32

• Sudden increase in intra-abdominal pressure following HBC (cats, dogs) or falls in horses can result in rupture of the diaphragm.
• Spontaneous rupture of muscles in racing greyhounds and horses can occur; especially the gastrocnemius m.
• Tearing of adductor muscles in cattle that do the splits on slippery floors . Results in severe damage that will include damage to muscle fiber basement membranes (heals by fibrosis).

Question 33

What is the cause of malignant edema? What is its othern name?

Answer 33

Also called gas gangrene.

• Acute fatal infection caused by wound infection with Cl. septicum, Cl. perfringens, Cl. novyi, Cl. sordelli and Cl. chauvoei alone or in combination.
• These are gram-positive bacilli to a greater or lesser degree anaerobic, and exist in the environment as resistant spores.
• When they proliferate in tissues they are highly toxigenic and induce extensive muscle necrosis

Question 34

In malignant edema, what are the location and presentation of the lesions? What do you see in histological slides? Who is this most common in?

Answer 34

Lesions primarily involve the subcutis- > edema, moderate emphysema, hemorrhage and discoloration of the
overlying skin

• Histo: Edema, cellulitis, minimal myositis.
• Malignant edema is most common in domestic ruminants and horses (most often 2ry to penetrating wounds)

Question 35

What is black leg?

Answer 35

(a.k.a.: black quarter, emphysematous gangrene): Acute, fatal necrotizing myositis of ruminants (mainly cattle) caused by Clostridium chauvoei.
• Characterized by activation of latent spores in muscle.

Question 36

What is the pathogenesis of black leg? Who is it most common in?

Answer 36

Pathogenesis: spores in the soil -> ingestion -> spores in muscle (latent) -> muscle injury/ hemorrhage -> local hypoxia -> germination of spores in muscles -> exotoxins -> edema/ myonecrosis -> emphysema -> generalized toxemia -> death in approx. 24 hrs

• Most common in cattle 9-months to 2 years of age

Question 37

What is seen in this image?

Answer 37

Black leg: Necro-hemorrhagic and emphysematous myositis (or rhabdomyositis). Clostridium chauvoei.

Question 38

What is trichinosis? Where does the parasite reside? Where can it be found in the world? What are the muscles commonly infected? Do affected animals usually have symptoms?

Answer 38

Trichinosis (Trichinella sp.). is a parasitic myositis and important zoonotic disease.
• Rare in Canada/ USA except in the far North – humans are infected by consumption of incomplete cooked meat from pork, bears or aquatic mammals (debilitating disease with death due to myocarditis).

• Skeletal muscle is the habitat for the larvae of the nematode T. spiralis or nativa (colder climates) which becomes encysted in the muscle.
• Muscles of the tongue, the masseter, diaphragm, intercostals and ocular muscles are commonly infested.
• Affected animals are usually asymptomatic.

Question 39

What is seen in these histological slides?

Answer 39

Trichinella sp. – skeletal muscle

Question 40

What is cysticercosis? Where is the adult stage located in the definitive host? Where is the larval stage present? How are humans infected?

Answer 40

• Cysticercosis: Important zoonotic disease.
• The cysticercus is the larval stage of a taenia (Platyhelminth parasite ) -> tapeworm.
• The adult stage is in the intestine of the definite host (humans, dogs, wild carnivores). The larval stage (cysticercus) is in the muscle of the intermediate host (pigs, cattle, moose, reindeer etc.).
• Cysticercosis in humans is the result of ingestion of taenia eggs, not from ingestion of cysticerci.

Question 41

What is the cause of the lesions in this image?

Answer 41

Parasitic myositis

Question 42

What is sarcocystosis? What can sarcocystosis cause in patients? Who is the definitive host?

Answer 42

Sarcocystosis: Important and common protozoal disease affecting the striated muscle of a wide range of animals, specially cattle, sheep and poultry.
• Thin-walled cysts filled with bradyzoites within striated muscle

• Carnivores (dogs, cats, human beings) are the definite host.
• Sarcocystosis is often considered an incidental finding (minimal or no host response).
• Although muscle lesions are not important the disease is considered by some an important cause of abortion.

Question 43

What is seen in these images?

Answer 43

Sarcocystosis

Question 44

Where can toxoplasma be found?

Answer 44

Other parasites such as Toxoplasma, which can also cause muscle lesions are mentioned in other systems (cardiovascular, nervous, reproductive etc.,).

Question 45

What is masticatory myositis? What is the pathogenesis? What is the acute and chronic form?

Answer 45

• Immune-mediated myositis restricted to the masticatory muscles in dogs.
• Eosinophilic myositis and atrophic myositis, previously reported as 2 separate disorders, are now considered to be 2 ends of the spectrum in a single disease (acute and chronic form).
• Unclear pathogenesis –autoantibodies against a unique myosin isoform present in masticatory muscles: type 2M myosin
• Swollen painful jaw. Affected dogs are unable to fully open their mouths (trismus)

Question 46

What are the symptoms of masticatory myositis? What muscles are mostly involved? What breeds are predisposed? What can be seen in later stages?

Answer 46

Lesions are bilateral and progressive

• Muscle swelling or atrophy are more marked in the temporal and masseter muscles
• German Shepherds appear to be predisposed.
• Late stages are characterized by marked atrophy and fibrosis

Is there an endocrine component?

Question 47

What is Dematomyositis? What breeds is it commonly seen in? What is the disease characterized by? What causes recovery?

Answer 47

• Familial disease in Collies and Shelties
• Possible immune mediated etiology
• The disease is characterized by dermatitis (face, ears, tip of the tail and over bony prominences) and myositis (masticatory muscles).
• Most dogs recover spontaneously.

Question 48

What is occuring in this image?

Answer 48

Dermatomyositis

Question 49

What are the primary tumors of skeletal muscle? Are they benign or malignant? Who is each tumor most common? Where do they origniate typically?

Answer 49

• Rhabdomyoma: Benign and generally congenital. More common in cattle, sheep and pigs. Most originate in the heart (66%).
• Rhabdomyosarcoma: Aggressive local behaviour with frequent metastasis. Metaplastic rhabdomyosarcomas arising from sites with no striated muscle occur sporadically (kidney, urinary bladder, meninges). Embryonal rhabdomyosarcomas, usually involving the head or neck occur in young or young-adult individuals.