Unit 1 - Myopathies (Intro to Exertional Rhabdomyolyisis) Flashcards
When you have a potential myopathy patient, what questions do you want to ask about their history?
duration of illness, recurring problem, precipitating factors, exercise schedule, diet, vaccination history, number of animals affected, and familial relationships
What will you find on a general physical exam in a patient with a myopathy?
tachycardia, tachypnea, excessive sweating, and anxiety
What will you find on a muscular system evaluation in a myopathy patient?
firm, painful, and swollen muscles, muscle fasciculations, muscle atrophy, gait abnormalities, reluctance/refusal to move, recumbency, and inability to rise
What differential diagnoses should be considered along with myopathies?
gastrointestinal disease (colic), respiratory disease (pleuropneumonia), musculoskeletal disease (laminities or other lameness, fracture), neurologic disease ( a lot) electrolyte imbalance, and aorto-iliac thrombosis
What diagnostic tests are important for myopathy diagnosis?
serum chemistry and urinalysis
What ancillary tests help with confirming myopathy diagnosis?
CBC, vitamin E/selenium, blood gas analysis, fractional excretion of electrolytes
What will a serum chemistry show in a patient with a myopathy?
Electrolyte changes - increase P and K, decreased Na, Cl, and Ca
Increase BUN and Creatinine
Increase in creatine kinase (CK) and aspartate aminotransferase (AST)
What secretes creatine kinase?
skeletal muscle, myocardium, and the brain
When do increases in CK occur due to insult?
4-6 hours post insult
What is the 1/2 life of CK?
very short - 2-9 hours
What secretes AST?
skeletal muscle, cardiac muscle, the liver, RBC, and others
When do increases in AST occur due to insult?
12-24 hours post insult
What is the 1/2 life of AST?
very long - 7-10 days
What is creatine kinase a sensitive indicator for?
myonecrosis
What can cause a mild increase (<5000) in CK?
IM injection, strenuous exercise, recumbency/colic, and transport
What can cause a marked increase (10,000 to greater than 100,000)?
severe rhabdomyolosis
What does persistent elevation in CK indicate?
continuing myonecrosis
What will you see in a UA from a myopathy patient?
myoglobinuria
What does myoglobinuria indicate?
severe muscle damage
Why would electromyography help in diagnosing myopathies?
it will help determine whether the cause is myopathic or neuropathic and will aid in determining the distribution of the disease
What does thermography do?
it measures the skin surface temperature and alterations in blood flow
What does the exercise challenge test detect?
subclinical cases of chronic ER
How do you do an exercise challenge>
Have the patient do light, submax exercise (15-30 minutes) and evaluate CK before and 4-6 hours after it
What result on an exercise challenge test is indicative of exertional rhabdomyolysis?
> 3-4x increase in CK post submax exercise
What is used for genetic testing in regards to myopathies?
mane or tail hairs (with roots) or whole blood
What diseases can be detected with genetic testing?
hyperkalemic periodic paralysis (HYPP), polysaccharide storage myopathy (PSSM), malignant hyperthermia (MH), glycogen branching enzyme deficiency (GBED), immune-mediated myositis (MYH1M)
What are the two different ways myopathies are classified?
by cause or by clinical signs
What are the different types of rhabdomyolysis?
exertional and non-exertional
What is rhabdomyolysis?
destruction of striated muscle cells
What are the different types of exertional rhabdomyolysis?
chronic or sporadic
What are the different causes of non-exertional myopathies?
infectious, nutritional, toxic, and traumatic
What are the treatment goals for rhabdomyolysis?
relieve pain and anxiety, correct electrolyte and acid-base abnormalities, limit muscle damage, maintain perfusion, prevent pigment nephropathy, and provide supportive care
What treatments can be used for rhabdomyolysis?
sedatives, tranquilizers, analgesics, IV fluid therapy, antioxidants, muscle relaxants
What muscle relaxants can be used to treat rhabdomyolysis?
Methocarbamol, Guaifenesin, Dantrolene, and Paenytoin
How does methocarbamol and Guaifenesin work?
they are centrally acting, with the exact mechanism unknown - sedative effects
How does dantrolene work?
interferes with release of Ca from the SR
How does phenytoin work?
it acts on ion channels in muscles and nerves (promotes Na efflux) which decreases the sensitivity of muscle spindles to stretch
It is an anticonvulsant and antiarrhythmiac
What are the types of chronic exertional rhabdomyolysis?
PSSM, recurrent ER, and idiopathic
What are the causes of sporadic exertional rhabdomyolysis?
dietary and overexertion
What dietary changes can cause sporadic exertional rhabdomyolysis?
increased CHO, decreased Vitamin E/Se, decreased Na or K, and Ca/P imbalance
What breeds is polysaccharide storage myopathy (PSSM) common in?
quarter horse related breeds, draft horses, and warmbloods
What is polysaccharide storage myopathy?
When there is an accumulation of glycogen AND amylase-resistant abnormal polysaccharide in skeletal muscle leading to repeated episodes of exertional rhabdomyolysis
What gene is associated with type 1 PSSM?
GYS1 gene - there is a gain of function mutation (an autosominal dominant trait) that leads to elevated GS activity
What is type 2 PSSM?
The genetic mutation has not been identified, but there is an inconsistent accumulation of abnormal polysaccharide
What is the prevalence of PSSM in quarter horses and of that percentage, what percentage of those cases is type 1?
10% prevalence - 72% of those cases is due to type 1
What is the age of onset of PSSM in quarter horses and clinical signs?
average onset is 5 years (1-14 years) - exertional RM, abnormal gait, and muscle wasting
What is the prevalence of PSSM in draft breeds and of that percentage, what percentage of those cases is type 1?
40% prevalence - 87% of those cases is due to type 1
What is the age of onset of PSSM in draft breeds and clinical signs?
8 years - subclinical clinical signs, abnormal gait, muscle wasing, exertional rhabdomyolysis, and postanesthetic myopathy
What is the prevalence of PSSM in warmbloods and of that percentage, what percentage of those cases is type 1?
The prevalence is unknown, but 18% of the diagnosed cases is due to type 1
What is the age of onset of PSSM in warm bloods and clinical signs?
8-11 years - firm/painful hindquarters, abnormal gait, and exertional rhabdomyolysis in less than 15% of the cases
What are the clinical signs of mild forms of rhabdomyolysis?
exercise intolerance, pawing post exercise, muscle fasciculations, sweating, stiffness, urination stance, tucked-up abdomen
What are the clinical signs in severe forms of exertional rhabdomyolysis?
severe pain resembling colic, recumbency, and renal failure
What mutations leads to more severe and occasionally fatal forms of exertional rhabdomyolysis?
PSSM mutation with malignant hyperthermia
How is PSSM diagnosed?
genetic testing for the mutation and gluteal or semimembranous muscle biopsy with periodic acid-schiff stain for glycogen
What will a periodic acid-schiff stain show if a patient has PSSM?
2 fold increased density of glycogen, abnormal PAS positive inclusions, and subsacrolemmal vacuoles
Which fibers are mainly affected with PSSM?
type 2 fibers (fast twitch)
What are the two management techniques for PSSM?
dietary and exercise management
What are the recommended changes for dietary management of PSSM?
decrease the NSC carbohydrates (should be less than 10%) with alfalfa/grass hay mix or grass hay, and increase the fat content (greater than 13%)
What are some products with a high fat content?
Re-Leve, envision classic, nutrena empower, purina ultium, moorman’s natural glo or moorglo, equi-jewel, and corn oil
What do you want to do for exercise management of PSSM?
give them regular exercise or access to the paddock
Why would you want to increase exercise in PSSM patients?
burn their glycogen stores and enhance the oxidative capacity of muscle by increasing enzymes that utilize fat as fuel
What causes recurrent exertional rhabdomyolysis (RER)?
an inherited autosomal dominant trait in thoroughbreds that causes defective intracellular Ca regulation
What thoroughbred patients is RER the most common in?
fit young fillies in training at the racetrack
What clinical signs are assoicated with RER?
nervous temperament, poor performance, muscle stiffness, and rhabdomyolysis
How do you prevent RER?
minimize stress, daily exercise, turn-out, decreased carbs, fat supplementation, and give Acepromazine, dantrolene, and phenytoin before training exercise
