Exertional rhabdomyolysis means that the muscle fibers themselves are
separating, or "dissolving" in a way. There are several muscle
diseases that show similar signs, but there are 2 basic types of
exertional rhabdomyolysis. 1) acute; and 2) recurrent
The primary difference is that the acute form shows up suddenly after
exercise with no previous history of this problem, and may leave the
horse mildly affected to recumbant. The recurrent form
may occur repeatedly over a lifetime in mild or moderate form and
results in general poor performance. Signs for both can include a short and
stiffened gait. elevated respiration, profuse sweating, rapid heart
rate, increased temp., and in some endurance horses severe dehydration ,
synchronous diaphragmatic flutter (thumps), and collapse.
Diagnosis is based on history, enzyme levels in the blood, and
sometimes evaluation of urine, which may appear brown in severe cases
from leakage of muscle proteins. Treatment tries to alleviate pain,
correct electrolyte problems, and protect the kidneys.
The acute form cause may be just that the exercise is too strenuous
for the horse at that time. Outbreaks of repiratory disease may also
trigger the acute form (influenza and herpes virus 1). The exact
metabolic problem is unknown, but may involve electrolyte imbalance,
or problems with the muscle membrane.
The recurrent form is more mysterious, but usually occurs after
exercise as well. Diet and exercise protocols are the most likely
predisposing causes. High soluble carbohydrate diets (grains) and a
day of stall rest after heavy work have been shown to trigger
attacks. Vit. E /Selenium deficiency can cause the acute form, but
many horses with the recurrent form do not show this, and there is no
evidence to suggest extra protection from feeeding high levels of Vit. E.
Feeding too much Selenium is potentially toxic to horses and SHOULD
NOT be attempted. Other predisposing factors for the recurrent form
may be hypothyroidism, metabolic enzyme disorders, or electrolyte
regulation problems.
There is current and active research going on at
this time at several places, including UPenn's New Bolton Center (Dr.
Jill Beech), and the Swedish Univ. of Ag. Science (Dr. Stephanie
Valberg). Hopefully, we will be able to understand much more in the
future. Hope it helps!!!! Cheers...
Lynn Taylor, MS, PhD
Otterbein College
Westerville, Ohio
email: ltaylor@otterbein.edu