Muscular Problems Have Varied Causes

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A study from the University of Minnesota looked at the biopsy findings on muscle samples from warmblood horses submitted to their Neuromuscular Diagnostic Laboratory. Owners were also asked to complete a questionnaire regarding symptoms and compare the management of the affected horses to a normal control.

Symptoms prompting the biopsy were varied and included gait abnormalities (e.g., things like traveling wide behind, stiff gait, difficulty turning, toe scuffing, etc. would be considered a gait abnormality), actual tying-up, ”shivers,” muscle fasciculations (spontaneous muscle twitching) and atrophy. A total of 132 muscle biopsies were included. Diagnoses were:

EPSM ??? 54.5%

Recurrent exertional rhabdomyolysis ??? 5.3%

Neurogenic or myogenic atrophy ??? 5.3%

Nonspecific myopathy ??? 10.6%

Normal biopsy ??? 24.2%.

Of 45 owners who implemented daily exercise and diet change (low starch, added fat), approximately 70% reported improvement at six months.

This study highlights the importance of getting an accurate diagnosis. Gait changes or obvious muscle problems tend to get blamed on EPSM automatically, but only slightly higher than 50% of these horses actually had EPSM. It also shows that muscle problems can’t necessarily be diagnosed from symptoms alone, since almost 25% of these horses actually had normal muscle biopsies.

Muscle biopsy is a simple procedure and should always be done when a muscle problem is suspected. Other helpful diagnostic tests include:

• Complete lameness examination

• Full neurological examination

• Blood muscle enzyme levels

• Blood electrolytes, calcium and magnesium

• Blood vitamin E and selenium levels.

Bottom Line

Don’t automatically jump on the EPSM band wagon. The low-starch, high-fat diet is not a cure-all. It’s also not necessarily safe (see story below on fat and insulin resistance).

The potential complications of this diet include excessive weight gain, development of insulin resistance (with a risk of laminitis), inadequate fiber, protein and carbohydrate intake when fat levels are high and the remainder of the diet is severely restricted because of weight gain, fat interference with magnesium absorption, requirement for higher vitamin E intake and suppressed fermentation of fiber in the large bowel. The diet would not help, could even worsen, 35% of the horses tested. While waiting several months to see if the diet was going to work, the real cause would go undiagnosed and untreated. (For additional information understanding pathology, see article with Dr. Beth Valentine, page 20.)