Recurrent Exertional Rhabdomyolysis

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Recurrent Exertional Rhabdomyolysis

• Kelly Kauber

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Exertional Rhabdomyolysis

• Common Names
• Tying Up
• Azoturia
• Monday Morning Disease
• Chronic Intermittent rhabdomyolysis

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Exertional Rhabdomyolysis

• Underlying myopathy which is breed dependent
• Recurrent Exertional Rhabdomyolysis in
  Thoroughbreds
• Polysaccharide Storage Myopathy in Quarter Horses
• Equine Polysaccharide Storage Myopathy in Draft
  horses
• Over Exertion
• Diet - high carb load
• Fitness level

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Recurrent Exertional Rhabdomyolysis

• Affects Thoroughbreds
• 5 of racehorses are affected
• Primarily racehorses however it is also seen in a
  variety of thoroughbreds performing many
  disciplines including
• Three day eventers
• Steeplechasers
• Polo ponies
• Show jumpers

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Causes, Triggers and Predispositions

• Autosomal recessive inheritance
• Females are affected more often than males
• High Strung or nervous behavior
• Gallop training triggers onset rather than
  breezes or races
• High concentrated feeds (COH) carbohydrates
• Overexertion of unfit horses

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Clinical Signs

• Muscle cramping
• Hind end especially
• Increased heart and respiratory rate
• Stiff/unwilling to move
• Sweating
• Anxiety
• Discomfort/ lameness
• Firm muscles
• Softness can occur where tears or edema occurs

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What is going on?

• Cellular regulation of calcium is abnormal and
  interferes with muscle contraction.
• Basically the horse is suffering from severe
  muscle cramping and pain, it is important to
  realize that this disorder can cause damage to
  the muscle. Proper treatment and care is
  necessary to prevent lasting damage and future
  episodes
• Worst case scenario Recumbence and death
• If severe case is left untreated

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Two Classifications of Cases

• Sporadic- Overexertion
• Horse has no history of tying-up, usually occurs
  due to a muscle strain, inadequate warm up, lack
  of fitness, heat exhaustion, dehydration
• Moderate to high muscle damage
• Recurrent- Genetic
• Abnormal intracellular calcium regulation,
  nervous behavior, more common in fillies, and
  young horses
• Episodes usually occur during gallop training
  breezing or races.

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What to do

• This disorder can be serious, it is important not
  to afflict further damage on the horse.
• Dont force the horse to move too quickly
• Mild cases can be walked back to stall
• Severe cases shouldnt be moved
• Cover with cooler to keep from getting chilled
• Call the veterinarian- to determine cause
• It may be necessary to put the horse on IV fluids
  to rehydrate and prevent renal failure

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Diagnostic Tests

• Blood Tests can be performed to check for
  elevated muscle enzymes
• Creatine Kinase
• Aspartate Amino-transferase
• Myoglobinuria
• Urinalysis
• Myoglobin or degraded muscle in urine
• Urine is dark and red/brown tinted
• Muscle Biopsy taken from gluteal and
  semimembranous muscle (slow twitch)
• Look for lesions

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Treatment

• IV may be administered to rehydrate horse quickly
• Anti-inflammatories are sometimes given to reduce
  muscle inflammation
• Depending on severity- hand walking and light
  exercise are recommended as stall rest can make
  condition worse
• Muscle relaxants - sometimes used
• Phenytoin
• Dantrolene

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Prevention

• Reduce stress of the horse
• Environment
• Less stable confinement
• Regular exercise program
• Can help reduce occurrences
• Reduce starchy COH in feed
• High fat, low starch diet recommended
• Many feeds available on the market

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Summary

• It is an inheritable defect, but
• Management is key
• Be aware of the fitness level of the horse
• Proper warm up and cooling out
• Regular program and turn out
• Try to keep nervous horses as quiet as possible
• Adequate diet is important for high performance
  horses
• High fat, low carb
• A horse with RER is just as competitive as a
  horse without it, as long as it is managed
  correctly!

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Bibliography

• Loving, Nancy S. Incidence and Management of
  Exertional Rhabdomyolysis. The Horse July 03 2007
• MacLeay, Jennifer M. DVM, PhD Stephanie J.
  Valberg, et al. Recurrent Exertional
  Rhabdomyolysis in Thoroughbred Racehorses Effect
  of Diet and Exercise Intensity. AAEP PROCEEDINGS
  9 Vol. 45 / 1999
• Piscopo, Susan. DVM. Medicinal Control of
  Tying-Up. Equine Veterinary Journal, 35 (7)
  707-710, 2003.
• Ulman, Katherine. Equine Exertional
  Rhabdomyolysis. ADDL-West Lafayette. 2000
• Sampson, Sarah N. DVM. VMS 367 Myopathies.
  Washington State University. 2006
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