Page 413 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

388 CHAPTER 1

VetBooks.ir Diagnosis • Monitoring of plasma muscle enzyme activity
can be useful in guiding ongoing exercise
As changes on histopathology of muscle biopsy
samples in cases of RER are non-specific, and a
specific genetic mutation has not been identified, regimes. A sample at 24–48 hours will allow the
peak AST activity to be determined. If muscle
a diagnosis of RER is currently made on the basis enzyme activity does not continue to fall, this
of the clinical history and elevated muscle enzyme would suggest ongoing muscle injury.
activity in a Thoroughbred, Standardbred or related
horse. Evidence of previous muscle damage without Clinical signs in horses with RER are minimised
abnormalities associated with PSSM on histopathol- by feeding a diet low in starch, while providing nec-
ogy is also supportive. In severe cases, blood samples essary calories in the form of fat. The diet should
should be taken to assess hydration, electrolyte levels also provide high-quality forage and a balanced vita-
and renal function. Urinalysis may demonstrate a min and mineral supplement.
myoglobinuria in severe cases. Regular daily exercise with no rest days is essential.
Avoiding any sudden changes in exercise patterns and
Management providing adequate warm-up and cool-down periods
The treatment of the patient with acute rhabdomy- is essential. Daily turnout is recommended. Stress and
olysis is the same, regardless of the underlying cause. changes in routine can trigger clinical episodes and
The aims of treatment are to correct dehydration therefore minimising these factors is advised.
and maintain diuresis, prevent further muscle dam- Dantrolene sodium (Dantrium™) is a drug that
age and provide analgesia. This is achieved by: prevents the release of calcium from the sarcoplas-
mic reticulum within muscle. It has been shown to
• Fluid therapy. In the face of pigmenturia or reduce muscle enzyme activity and the clinical signs
marked hypovolaemia, intravenous fluids are of rhabdomyolysis in Thoroughbreds in training. It is
preferred. Crystalloids such as compound given orally 1–2 hours prior to exercise. Dantrium™
sodium lactate are recommended. In less severe is not licensed for use in horses; however, the British
cases where myoglobinuria is absent, oral fluid Horseracing Authority has suggested a detection
may suffice. time of 48 hours when a dose of 500 mg is given daily
• NSAIDs such as a meloxicam, flunixin for 3 days, although this may change in the future.
meglumine or phenylbutazone are useful
analgesics. Care must be taken in the Prognosis
hypovolaemic patient to avoid renal injury. The prognosis is determined by the severity and fre-
• Acepromazine may be beneficial in maintaining quency of clinical bouts and the response to treat-
muscle perfusion and reducing anxiety in a ment. Many horses, with appropriate management
stressed patient, but should be used with care in changes, can fulfil a useful athletic career, although
dehydrated patients. this is not always the case. Chronic recurring cases
• Antioxidants such as vitamin E (4000–6000 may develop muscle fibrosis or atrophy. Very severe
IU p/o daily) may help scavenge increased free cases that are recumbent may die or be euthanased.
radical production.
• Horses should initially be rested in a quiet PolysacchaRide stoRage myoPathy
stress-free box to prevent further muscle tyPes 1 and 2
damage, although gentle walking may be
beneficial within 1–2 days. Gradual increases Aetiology/pathophysiology
in hand walking can also be supplemented, PSSM was first described in Quarter horse and
with small paddock turnout followed by return Appaloosa-related breeds and has subsequently
to ridden exercise when enzyme levels have been identified in a variety of different breeds
returned to normal. across Europe and North America (Table 1.5).