Stephanie Valberg, DVM, PhD, professor of large animal medicine and director of the University of Minnesota’s Equine Center, started an in-depth seminar on muscle disorders by discussing diagnosis of muscle disorders, beginning with a careful physical exam and concise history of the clinical problem. She said in most cases, a muscle disorder arises from one of the following situations: muscle strain, exertional rhabdomyolysis (tying-up), weakness and exercise intolerance, abnormal muscle contraction and nerve conduction, or muscle atrophy. Identifying the exact nature of a horse’s muscle problem is dependent on characterizing the clinical signs to narrow down the problem.

Careful inspection of a horse’s muscle mass and symmetry and hands-on palpation educates the examiner about the horse’s muscle tone and comfort level. The examiner also evaluates the horse in motion and conducts a full lameness exam. A serum chemistry panel is helpful for biochemical analysis of muscle enzymes that provide telling information about muscle health and the duration of muscle injury.

There are some enzymes that can yield information about muscle, although not all of these enzymes are found exclusively in muscle. Serum creatine kinase (CK) is released within just a few hours of muscle damage, peaking within six hours following injury. Elevations in CK are usually consistent with training, transport, or taxing endurance or eventing competition. Higher levels from these causes generally are within an expected range and should return to normal quickly, whereas a horse experiencing rhabdomyolysis will have extreme increases in CK.

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