Diagnosing Muscle Atrophy in Horses

Our first topic is muscle atrophy in horses. This 3-part post discusses the causes of muscle atrophy, how atrophy is diagnosed and how it can be treated.

Muscles of the head, neck, and trunk play a crucial role in the horse’s posture, movement, and performance. Unfortunately, muscle atrophy within these spinal regions may be overlooked or dismissed as not being clinically relevant. Early detection is essential to address any underlying contributing factors to prevent additional muscle loss and associated weakness. In this article, we will review diagnostic methods for identifying muscle atrophy in horses.

Recognizing the signs

Detecting muscle atrophy can be challenging as it may progress gradually over time and not be readily apparent or may be considered normal. Oftentimes, a member of the horse’s care team who sees the horse on a regular basis, such as a bodyworker, will call the owner’s attention to the atrophied area and suggest that their veterinarian be consulted.

Horses with muscle atrophy often have characteristic clinical signs:

  1. A hollowed-out appearance in the muscles of the neck, caudal withers, back, or pelvic regions
  2. Flexor-extensor muscle imbalances or left-right asymmetries in muscle development
  3. Changes in posture or head and neck carriage
  4. Reduced performance or inability to engage in certain movements

Diagnostic techniques
When muscle atrophy is suspected, it is important to consult with an experienced equine veterinarian for a comprehensive diagnosis. A combination of diagnostic procedures may be required to identify the affected muscles and potential underlying cause of muscle atrophy:

  1. Medical history: Information about the onset of muscle atrophy, appetite, type and quality of foodstuffs, and concurrent pain or lameness are useful.
  2. Physical examination: A thorough evaluation is required to characterize the distribution of muscle atrophy as a local, regional, or whole-body issue.
  3. Muscle contours: The presence and severity of muscle atrophy can be assessed by grading muscle development as convex, flat, or concave.
  4. Muscle tone and texture: Palpation of affected areas may reveal hypertonicity (i.e., spasms), normal tone, or flaccidity.
  5. Symmetry: Generalized muscle wasting is often symmetrical, whereas muscle atrophy due to trauma or a nerve injury may be only present at a single site.
  6. Diagnostic imaging: Ultrasonography is useful to visualize left-right differences in muscle mass and to measure a muscle’s cross-sectional area.
  7. Electromyography (EMG): EMG is a diagnostic technique that measures the electrical activity of muscles. It can help determine if the muscle atrophy is due to an underlying muscle disease or due to nerve damage.
  8. Blood work: Analysis of muscle enzymes and vitamin E levels are useful to identify systemic diseases or nutritional deficiencies that contribute to atrophy.
  9. Genetic testing: Several genetic disorders have been linked to muscle atrophy, which can be readily confirmed with hair samples or muscle biopsies.

The diagnosis of muscle atrophy in horses requires a systematic and comprehensive approach.  Early detection and prompt intervention are key to preventing further muscle loss and to address the underlying cause. An accurate diagnosis is required to develop a focused and effective treatment plan.

Read the complete 3-part series: Muscle Atrophy in Horses

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