3 breeds that exertional rhabdomyolysis is seen in
What is PSSM?
polysaccharide storage myopathy
-glycogen storage disorder in the type II fast twitch muscle fibers
Difference between type I and type II PSSM
type I: changes in muscle tissue, DNA mutation in glycogen synthase gene
type II: changes in muscle tissue, no DNA mutation; something else has resulted in the PSSM
What 2 enzymes are elevated in PSSM horses?
CK and AST
Why are these PSSM horses brought to the hospital?
exercise intolerance, muscle atrophy, gait abnormalities
How can you test for PSSM?
15 min exercise test
measure CK in 4-6 hrs
What is malignant hyperthermia (MH)?
RyR1 gene muatation
excessive release of Ca into the myoplasm induced by anesthetics, stress
c/s of MH horses
heat, hypercapnia, lactic acidosis, extremely rigid muscles
If PSSM & MH occur concurrently, what happens?
Severe tying-up signs
What would you see on muscle biopsy in PSSM horses?
Different sized muscle fibers
PAS stain picks up carbohydrate accumulation
Where do you take the muscle biopsy from?
Can you biopsy muscles at birth to detect disease?
no, takes a couple years to see changes & accumulate glycogen
can do glucose tolerance or DNA testing
What is best diet & environment for PSSM horses?
low carb diet
on pasture grazing & moving around
What is the mode of inheritance for PSSM?
What is the average age you see horses with PSSM?
5 yrs (when starting to train for their 'job')
What time during exercise do the horses start showing signs?
early in exercise
c/s of PSSM
muscle pain, stiffness, high HR
What is the difference between quarter horse PSSM & draft horse PSSM?
Draft horses also have the mutation in the GYS1 gene
Normal muscle enzyme levels
c/s of PSSM seen in draft breeds
weakness, difficulty rising
What is shivers?
seen in draft breeds & warmbloods
elevation of hind limbs & shaking it
Can drafts have both shivers & PSSM?
What kind of diet can help with shivers?
Do warmbloods have full-blown PSSM?
How should you manage PSSM horses after an episode?
Rest for 48 hrs, then turnout in small pen
sedation necessary for excitable horses
Why do you want to slowly ease the horse back into exercise?
careful exercise enhances oxidative capacity of the muscle
What type of diet is best for PSSM horses?
Use fat as energy source
During the acute episode, what should you do?
Reduce pain w/ sedation, NSAIDs or opioids
Fluid therapy to dilute out pigement from the muscles running through the kidneys
How long should you continue fluids?
1-2 days after urine appears clear
What is the presentation of recurrent ER in thoroughbreds?
Seen mostly in nervous fillies early in course of exercise
c/s of RER
stiff painful muscles
What causes RER?
abnormal excitation-contraction coupling
What is the defect leading to RER?
abnormal intracellular Ca resulting in inc. myoplasmic Ca
What does the muscle biopsy look like?
muscle necrosis & regeneration
How can you manage a thoroughbred after case of RER?
-daily turnout for 2 wks
-mild sedation if needed
What are dantrolene & phentoin for?
dantrolene: inhibits Ca release from the SR
phentoin: alters Na and Ca channels
What diet is best for RER patients?
What if the thoroughbred had continuous episodes, can you keep it on the meds?
no, can't be on chronic medication
probably won't race anymore
What other meds can be given after acute RER episode?
NSAIDs, butorphanol for analgesia
Ace, xylazine, detomidine for anxiety
Diazepam for muscle relaxation
What causes immune mediated myositis?
exposure to Strep. equi
natural or vaccination
How to diagnose Strep myositis?
M protein titers
What would muscle biopsy show for Strep myositis?
lymphocyte infiltration around the muscle fibers
Txt for Strep myositis
Parenteral or oral corticosteroids
Why do you want to use antibiotics when treating immune-mediated myositis?
Corticosteroids are immunosuppressive & strep. equi may still be present