Pathology of Skeletal Muscle, Pt. 2 Flashcards
What is arthrogryposis? What is it typically associated with?
congenital condition in aborted fetuses and stillborns characterized by rigid joints and limbs in abnormal, grotesque positions
developmental abnormalities of the nervous system (spina bifida, syringomyelia) that causes a lack of innervation, which leads to muscle hypoplasia
Other than denervation, what is another probable cause of arthrogryposis?
ingestion of toxins
in-utero viral infections
(Akabane disease, Cache Valley fever, blue tongue)
What is muscular dystrophy? Dogs and cats are models for what type of muscular dystrophy?
genetical determined, progressive, degenerative disease of the muscle where regenerative attempts are inadequate or absent
Duchenne’s muscular dystrophy
What causes Duchenne’s muscular dystrophy?
animal or person affect lack dystrophin, a cytoskeletal protein that strengthens muscle and protects it from injury
In what kinds of dogs is the X-linked dystrophin gene defect most identified? What organs tend to be involved?
young male Golden Retrievers (Irish Terriers, Samoyeds, Labs, Rottweilers, Dalmations)
heart —> cardiomyopathy
esophagus —> megaesophagus
weakened diaphragm
What are the characteristic symptoms of the X-linked dystrophin gene defect leading to muscular dystrophy? What typically causes death in patients with this?
muscle wasting
outward rotation of forelimbs (splaying)
aspiration pneumonia
cardio-respiratory failure
What is Equine Polysaccharide Storage Myopathy (EPSSM)? How can this be diagnosed microscopically?
inherited disease reported mainly in QH, Arabians, Morgans, Ponies, and draft-related breeds, where an underlying carbohydrate metabolic disorder causes gate abnormalities (hind limb lameness) and reduced muscle mass
accumulation of PAS positive material (polysaccharides) in muscle associated with Type II fibers
What is Porcine Stress Syndrome? What pigs are more susceptible? Why have instances dropped?
(porcine malignant hyperthermia)
an inherited hypermetabolic syndrome characterized by dyspnea, muscle rigidity and convulsions, hyperthermia, lactic acidosis, hyperkalemia, cardiovascular collapse, and death
heavy-muscle pigs
genetic testing
What causes Porcine Stress Syndrome?
single point mutation in the skeletal muscle ryanodine receptor gene (ryr1), which is a calcium release channel
the mutation in this gene causes uncontrolled calcium release, which leads to the excessive muscle contraction and heat production
What characteristics point toward Porcine stress syndrome during a necropsy? What muscles are most affected?
pale, swollen, and wet muscles (PSE = pale, soft, exudative)
longissimus dorsi and psoas
What secondary lesions are common in pigs that died due to Porcine Stress Disorder?
acute heart failure:
- pulmonary edema and congestion
- hydropericardium
- hydrothorax
- hepatic congestion
What are common microscopic characteristics of Porcine Stress Syndrome?
acute myofiber degeneration - interstitial edema, myofiber swelling, fragmentation, segmental contraction with “retraction cap”
What is White Muscle Disease? Why is it most common in young animals and those that are the best nourished and rapidly growing?
nutritional myopathy as a result of a vitamin E and selenium deficiency
these animals have the highest metabolism, leading to the production of oxygen radicals,; lacking in vitamin E and selenium (radical scavenger co-enzymes to glutathione peroxidase/reductase) leads to the lipoperoxidation of cell membranes
What are 2 other vitamin E/selenium syndromes that co-exist with nutritional myopathy in pigs?
hepatosis dietetica
mulberry heart disease
What leads to the “white muscles” of nutritional myopathy?
calcification (dystrophic mineralization)
What are 2 common clinical signs of White Muscle Disease? What muscles are most affected?
- stiffness
- dyspnea
those that are used the most and create the most free radicals
- intercostals in animals where there is little involvement of other muscles
- thigh in shoulders in cases of high skeletal muscle involvement
- tongue and neck muscles in nursing animals
Neck muscles, White Muscle Disease:
pale, granular mineralization appearance (gritty)
Thigh muscles, White Muscle Disease:
pale, hemorrhage
Nutritional Myopathy, histology:
sarcoplasm fragmentation
Nutritional Myopathy, heart:
white brush strokes - mineralization, chalky, gritty
How do lambs and calves differ in their presentation of White Muscle Disease in their heart?
LAMB - common in right ventricle
CALF - common in left ventricle
How can mineralization in White Muscle Disease be visualized histologically?
Von Kossa stain highlights calcium in a dark brown color
What are exertional myopathies?
group of diseases characterized by muscle damage initiated by muscle activity (can be intensive/exhaustive, but minimal exercise can cause damage in susceptible individuals)
What is hyperkalemic periodic paralysis (HYPP)? What is the underlying defect?
inherited condition that affects descendants of the famous QH, Impressive
characterized by well-defined muscle groups rewarded in halter competitions
alteration in muscle sodium channel, leading to a release of potassium in the bloodstream and extracellular space —> transient muscle spasms (myotonia), flaccid paralysis, death
What is Equine Exertional Rhabdomyolysis? Etiology is unclear, but what are some possible causes? What metabolic myopathy is common in horses affected by it?
(azoturia, paralytic myoglobinuria, Monday Morning Disease)
overexertion, exhaustion, dietary imbalances - electrolyte, vitamin E, selenium depletion
Equine Polysaccharide storage myopathy
What horse breed are more susceptible to Equine Overexertion Rhabdomyolysis?
heavy breeds
What muscles are most affected by Equine Exertional Rhabdomyolysis? How can it be diagnosed? What is the most common cause of death associated with this disease?
gluteal, femoral, and lumbar muscles become swollen and rigid
elevated levels of creatinine kinase and aspartate aminotransferase (indicative of muscle damage)
myoglobinuric nephrosis —> muscle breakdown releases a high amount of myoglobin in the blood, which can severely damage the kidneys
What is capture myopathy? 3 common lesions?
acute, often fatal disease seen most often in wild mammals and birds following strenuous activity (exertion) during capture or transport
- muscle degeneration/necrosis/hemorrhage
- ruptured tendon
- myoglobinuric nephrosis
What is Compartment Syndrome? Where is it commonly observed in veterinary medicine?
ischemic damage that occurs in muscles surrounded by heavy aponeurosis or bone sheaths (non-expandable compartments) when subjected to moderately vigorous contractions
supracoracoideus muscles in poultry following brief, but vigorous, flapping of the winds (deep pectoral myopathy)
Deep pectoral myopathy, Compartment Syndrome:
supracoracoideus muscle
What is Downer Syndrome? What causes it?
ischemic necrosis of ventral and limb muscles following prolonged recumbency, commonly from debilitating disease (like milk fever)
weight of the body on a limb tucked under the body for a long period of time results in increased pressure on the vasculature, leading to edema and ischemic necrosis
Why is Downer Syndrome so common in cows? Why is it a cruel cycle?
large animals in good body contition have healthy weight and muscle mass and they are susceptible to diseases where paresis is frequent
widespread muscle fiber necrosis makes it difficult to get up even when the cow overcomes sickness and lethargy
Downer cow muscle lesion:
pale, hemorrhage
Downer cow, ischemic necrosis
multifocal hemorrhagic necrosis
What is Equine Post-Anesthetic Myopathy? What does this entail for surgery?
condition similar to Downer Syndrome that occurs in 3-6% of cases in which general anesthesia is used - due to remaining the same position for a long time
important for procedures to be as fast as possible
What is Crush Syndrome?
syndrome similar to Downer Syndrome caused by acute trauma (like getting hit by a car) where increased pressure on vasculature causes necrosis in muscle
How can acute trauma, like getting hit by a car (dogs, cats) or falling (horses), affect the diaphragm?
increase in the intra-abdominal pressure can cause the diaphragm to rupture
What muscle is commonly ruptured in racing greyhounds and horses?
gastrocnemius m.
What muscle is commonly torn in cattle that slip on the floor? What does this result in?
adductor m.
severe damage that will include damage to muscle fiber basement membrane —> heals by fibrosis and second intention, leading to scar formation
What is malignant edema, aka gas gangrene?
inflammatory muscle disease caused by actue fatal infection caused by Clostridium septicum, perfringens, novyi, sordelli, and/or chauvoei, anaerobic bacteria that exist in the environment as resistant spores and can proliferate in tissue
- highly toxigenic and induce extensive muscle necrosis
What is characteristic of malignant edema (gas gangrene) lesions? In what animals is it most common?
subcutis edema, moderate emphysema, hemorrhage, and discoloration of overlying skin
HISTO: edema, cellulitis, myositis
domestic ruminants and horses, often secondary to penetrating wounds
What is Black Leg?
(aka: black quarter, emphysematous gangrene)
acute, fatal necrotizing myositis of ruminants (mainly cattle) caused by Chlostridium chauvoei and characterized by activation of latent spores in scapular muscle
What is the pathogenesis of Black Leg? In what age of cattle is this most common in?
spores of C. chauvoei found latent in the soil are ingested by the cattle and reach muscle; during muscle injury/hemorrhage and local hypoxia spores germinate in the muscles and produce exotoxins that can cause edema, myonecrosis, emphysema, generalized toxemia, and death within a day
9 mo to 2 yrs
Black Leg:
necro-hemorrhagic and emphysematous myositis (rhabdomyositis)
- gas bubbles produced by bacteria can cause muscle fibers to separate
What are the main muscles affected by Black Leg?
large muscle masses (scapular and pelvic girdles)
- also tongue, heart, diaphragm
What is Trichinosis? What 2 genera cause this? What muscles are most affected?
parasitic myositis, typically affecting individuals that consume uncooked meat from pork, bears, or aquatic mammals —> typically causes death due to myocarditis
T. spiralis and T. nativa (colder climates) larvae become encysted in skeletal muscles, commonly the tongue, masseter, diaphragm, intercostls, and ocular muscles
Trichinosis:
coiled parasite in skeletal muscle
Trichinosis, encysted larvae:
pale elongated foci throughout diaphragm
What is Cysticercosis? What are the different sites where the adult and larval stages are found?
parasitic myositis caused by the larval form of Taenia tapeworms (cysticercus), typically the ingestion of Taenia eggs from infected meat or water
ADULT: intestine of the DH; humans, dogs, wild carnivores
LARVAE: muscle of IH; pigs, cattle, moose, reindeer
Cysticercosis, pig heart
vesicular lesions
Cysticercus, pig skeletal muscle:
white nodules
What genus of Taenia come from pigs and is able to infect humans?
T. solium
What is Sarcocystosis? What is the definitive host?
parasitic myositis that is a common protozoal disease affecting the striated muscle of a wide range of animals, resulting in the formation of thin-walled cysts filled with bradyzoites
carnivores —> tend to be an incidental finding; minimal or no host response
Although Sarcocystosis tends to be an incidental finding, what is important to keep in mind?
important cause of abortion in pregnant animals
Sarcocystosis:
cyst + bradyzoites; no inflammatory response
Sarcocystosis, muscle fibers:
pectorals
What is masticatory myositis? What causes this?
immune-mediated myositis affecting the masticatory muscles in dogs
dog produced autoantibodies against a unique myosin isoform present in the masticatory muscles: type 2M myosin
What are the key symptoms of Masticatory Myositis? How do the lesions occur?
- swollen and painful jaw
- inability to fully open mouth (trismus); CT replaces muscle after necrosis
- atrophy of temporal and masseter muscles
- fibrosis
- problem eating —> weight loss
BILATERALLY and progressive
What breed of dog is predisposed to Masticatory Myositis?
German Shepherd
What is Dermatomyositis? What breeds of dogs are predisposed to it? How do most dogs recover?
possible immune-mediated etiology, characterized by dermatitis of the face, ears, tip of tail, and over bony prominences, and myositis of masticatory muscles
Shelties and Collies
spontaneously
What are the 2 types of primary tumors of skeletal muscles?
- Rhabdomyoma: benign and generally congenital - common in cattle, sheep and pigs; most originate in the heart
- Rhabdomyosarcoma: aggressive local behavior
- metaplastic: arising from sites without skeletal muscle (kidney, bladder, meninges) occurs sporadically
- embryonal: involves head/neck in younger individuals
