Unit 1 - Myopathies (Non-exertional Myopathies to end) Flashcards
What are the infectious causes of non-exertional rhabdomyolysis?
streptococcal and clostridial
What are the toxic causes of nonexertional rhabdomyolysis?
seasonal pasture myopathy, white snake root, and ionophores
What is the genetic cause of nonexertional rhabdomyolysis?
malignant hyperthermia
What are the traumatic/circulatory causes of nonexertional rhabdomyolysis?
compartment syndrome and postanesthetic (local)
What is compartment syndrome?
when the muscle fascia is unable to stretch - trauma causes increased pressure and ischemia
Malignant hyperthermia is a generalized post-anesthetic myopathy (usually). What is it due to?
sensitivity of muscle cells to halothane and succinylcholine
What are the triggering factors for non-anesthetic forms?
exercise, illness, stress, breeding, and concurrent other myopathies
What is the pathogenesis of malignant hyperthermia?
- mutation in Ryanodine receptor 1 gene
- Excessive Ca release from the SR due to the mutation
- muscle contracture
- hyperthermia
What clinical signs are associated with malignant hyperthermia?
anxiety, tachycardia, tachypnea, profuse sweating, hyperthermia, recumbency/struggling to rise, muscle rigidity, myoglobinuria, death with peracute rigor mortis
What signs do survivors of malignant hyperthermia have?
residual myscle atrophy, fibrosis, and scarring
What is the treatment for malignant hyperthermia?
treatment for rhabdomyolysis, alcohol/cold water baths, muscle relaxants, and sodium bicarbonate
How is malignant hyperthermia prevented (post-anesthetic forms)?
correct positioning, adequate padding during anesthesia, maintain mean arterial blood pressure, and dantrolene 1-2 hours before induction
What is nutritional myodegeneration also known as?
white muscle disease
What causes nutritional myodegeneration?
Vitamin E/Se deficiency
What population of horses typically gets nutritional myodegeneration?
fast growing foals from birth to 11 months of age
Mares of nutritional myodegeneration foals are typically on ______-deficient diet during gestation.
selenium
What are the two forms of nutritional myodegeneration?
skeletal and cardiac form
What are the clinical signs/conditions associated with the skeletal form of nutritional myodegeneration?
slow onset of muscle weakness, stiffness, hard/painful muscles, trembling, recumbency, dysphagia, aspiration pneumonia, and secondary sysetmic infections due to decreased immunity
What are the clinical signs/conditions associated with the cardiac form of nutritional myodegeneration?
acute onset respiratory distress, arrhythmias, cardiovascular collapse, and death
How is nutritional myodegeneration diagnosed?
elevated muscle enzymes, myoglobinuria, severe electrolyte abnormalities (decreased Na and Cl, increasd K and P), low blood Se and/or glutathione peroxidase levels, and response to Vit. E/Se
How is nutritional myodegeneration diagnosed post mortem?
bilateral symmetric myodegeneration, pale and dry appearance of muscle, and white streaks
What causes white streaks in muscle?
it could be due to coagulation necrosis, calcification, fibrosis
How do you treat nutritional myodegeneration?
exercise RESTRICTION, selenium and Vitamin E supplementation, and supportive care
What is the supportive care specifically for nutritional myodegeneration treatment?
correct electrolyte and acid base imbalances, antimicrobial and antiulcler therapy, and enteral feeding
What is the prognosis for nutritional myodegeneration?
guarded - 30-45% mortality in the skeletal form, and 95% in the cardiac form
How is nutritional myodegeneration prevented?
Se supplementation to pregnant mares and foals from birth to 6 months of age, access to good quality green forage
Where does nutritional myodegeneration occur if it does in adult horses?
muscles of mastication, locomotion, or cardiac muscle most commonly affected
What is seasonal pasture myopathy?
acute, severe rhabdomyolysis in pastured horses that is seasonal
Where has seasonal pasture myopathy been reported?
australia, canada, and the US (Minnesota in 2006, and Iowa and Wisconsin in 2009)
What is the case fatality rate associated with seasonal pasture myopathy?
75-95%
What clinical signs are associated with seasonal pasture myopathy?
acute weakness/stiffness, muscle fasciculations, myoglobinuria, recumbency, tachycardia, tachypnea/dyspnea, colic like signs, dysphagia, esophageal obstruction, and death (within 3 days)
What clinicopathologic data is associated with seasonal pasture myopathy?
very increased CK and AST, hyperglycemia, hypocalcemia, metabolic acidosis, and increased liver enzymes
What is the etiology of seasonal pasture myopathy?
Hypoglycin in seeds/seedlings of maple trees
What is the pathogenesis of seasonal pasture myopathy?
- hypoglycin inhibits mitochondrial enzymes
- Fatty acid beta oxidation is inhibited
- There is an accumulation of secondary (toxic) metabolies
- There is a lack of energy supply in tissues utilizing FA for energy production affecting postural, respiratory, and cardiac muscles?
How is seasonal pasture myopathy diagnosed?
muscle biopsy, oil red O stain, metabolic profiles (antemortem), toxic metabolite of hypoglycin
What muscles do you want to biopsy to test for seasonal pasture myopathy and why?
postural and intercostal muscles because they have a high oxidative capacity/type 1 myofibers
What do you look for in an Oil Red O stain?
paucity of cellular infiltrates - Zenker’s necrosis and lipid accumulation
What is the toxic metabolite of hypoglycin?
methylenecyclopropyl acetic acid
What are the risk factors of seasonal pasture myopathy?
overgrazed pasture, horses at pasture 24/7, little/no supplemental feed, and inclement weather
How is seasonal pasture myopathy prevented?
Prevent access to box elder seeds in fall/spring, supplemental feeding, and prevent stress that could trigger the development of clinical signs in subclinical cases
How do you treat seasonal pasture myopathy?
symptomatic with muscle relaxants, IV fluids, antimicrobials, 5% dextrose IV, frequent, small, carbohydrate rich meals, riboflavin, and antioxidants
What is clostridial myonecrosis?
rapidly progressive local necrotizing muscle infections within 2 days of intramuscular non-antibiotic injection or injury that leads to systemic toxemia
What etiologic agents cause clostridial myonecrosis?
C. septicum, chauvoei, perfringens (type A), sordelli, and novii - it is often a mixed infection
What clinical signs are associated with clostridial myonecrosis?
painful, hot soft swelling, severe depression, fever, tachycardia, tachypnea, anorexia, ataxia, dyspnea, recumbency, coma, and deathw ithin 12-24 hours
How is clostridial myonecrosis treated?
aggressive surgical debridement and fasciotomy to establish drainage and aeration (the preferred method), antibiotics, supportive care, and hydrotherapy
How is clostridial myonecrosis diagnosed?
history/clinical presentation, needle aspirate for a direct smear or anaerobic culture
What is the prognosis for clostridial myonecrosis?
guarded to poor
What are the Streptococcus equi associated myopathies?
severe acute rhabdomyolysis and infarctive purpura hemorrhagic (Henoch-Schonlein purpura)
What is immune mediated myositis (or polymyositis)?
rapid lumbar and gluteal muscle atrophy
What signs are associated with immune-mediated myositis?
stiffness, malaise, weakness, mild-moderate elevation of CK and AST, and an unremarkable CBC
What is the etiology of immune-mediated myositits?
a missense mutation in myoglobin heavy chani 1 (MYH1) gene in quarterhorses - autosomal dominant trait
What muscle cells does immune-mediated myositis affect?
type 2x myosin
What is the triggering factor in 40% of cases of immune mediated myositis?
exposure to strep equi or other respiratory disease
How is immune-mediated myositis diagnosed?
Tru-Cut biopsy of the epacial or gluteal muscle to look for atrophy of type 2 fibers and lymphocytic vasculitis or genetic testing
How is immune-mediated myositis treated?
corticosteroids and antimicrobials if there is a bacterial respiratory infection
What is the prognosis for immune-mediated myositis?
fair - muscle mass recovery within 2 months
What causes hyperkalemic periodic paralysis (HYPP)?
a point mutation in voltage gated sodium channels of skeletal muscle causing Na channels to fail to inactivate leading to an influx of Na and efflux of K
What breeds of horses typically get HYPP?
quarter horses, paints, and appaloosas
What clinical signs are associated with a mild episode of HYPP?
muscle fasciculations (neck, shoulder, flank), muscle cramps, sweating, prolapse of the third eyelid, muscular weakness
What clinical signs are associated with a severe episode of HYPP?
swaying, dogsitting, staggering, recumbency, laryngeal/pharyngeal paralysis, respiratory distress, collapse, and death due to cardiac rest
What clinical signs of HYPP are found in homozygous foals?
paralysis of upper respiratory muscles, respiratory stridor/distress, dysphagia, and aspiration pneumonia
How long do episodes of HYPP last?
15-60 minutes, spontaneous recovery is common, and longer if severe and untreated
What are the precipitating factors of HYPP?
fasting, anesthesia/heavy sedation, stress, trailer rids, dietary changes (increased K)
How is HYPP diagnosed?
hyperkalemia during episodes, mild hyponatremia, hemoconcentration, and DNA testing
How is HYPP treated?
gran, corn syrup, 5% dextrose, sodium bicarbonate, calcium gluconate, and acetazolamide
How is HYPP prevented?
a low K diet, feed several times/day, regular exercise or access to a paddock, and increased K excretion by giving acetazolamide and hydrochlorothiazide
What is glycogen branching enzyme deficiency (GBED)?
a fatal glycogen storage disorder of QH-related breeds
Is GBED caused by a recessive or dominant trait?
autosomal recessive trait
What does the mutation of GBED cause?
an accumulation of long unbranched chains of glucose primarily in skeletal muscle, cardiac muscle, and the liver
Who are the carriers of GBED?
they are heterozygotes that have half-normal GBE activity, normal histopathology and no clinical signs
What are the clinical signs of GBED?
Unspecific - weakness at birth, congenital limb contracture, inability to rise, decreased physical activity, respiratory failure, seizures, and sudden death
How is GBED diagnosed?
persistent mild elevations, elevated GGT, leukopenia, hypoglycemia, and genetic testing
What does a muscle biopsy of GBED show?
lack of normal PAS staining for glycogen and intracellular PAS-positive globular and crystalling inclusions
