Quantitative motor unit action potential analysis of supraspinatus, infraspinatus, deltoideus and biceps femoris muscles in adult Royal Dutch sport horses.
Authors: Jose-Cunilleras E, Wijnberg I D
Journal: Equine veterinary journal
Summary
# Editorial Summary: QEMG Reference Values for Sport Horse Muscle Assessment Quantitative electromyography (QEMG) offers objective diagnostic potential for neuromuscular conditions in horses, yet baseline reference ranges have been lacking for commonly assessed muscles. Cunilleras and Wijnberg established normative QEMG parameters for the supraspinatus, infraspinatus, deltoideus and biceps femoris in seven healthy Royal Dutch sport horses, measuring motor unit action potential characteristics including duration, amplitude, phases, turns, area and size index according to standardised protocols. Shoulder muscles (supraspinatus and infraspinatus) demonstrated significantly higher values across most parameters than hindlimb muscles, with supraspinatus duration ranging 8.7–10.4 ms and amplitude 651–867 µV, whilst biceps femoris showed considerably lower values (duration 5.7–7.8 ms, amplitude 265–385 µV); notably, polyphasic potentials exceeding 15% appeared in four of seven normal horses' shoulder musculature, indicating this finding alone doesn't indicate pathology. These reference intervals enable clinicians to distinguish normal variation from genuine neurogenic and myopathic disorders, with the marked muscular differences suggesting that muscle-specific thresholds are essential for accurate interpretation rather than applying universal criteria. For practitioners managing horses with suspected lower motor neuron disease or myopathy, QEMG now provides a more robust diagnostic framework—though interpretation requires understanding normal anatomical variation in motor unit characteristics.
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Practical Takeaways
- •When interpreting QEMG results in sport horses, muscle-specific reference values must be used — shoulder and hindlimb muscles have distinctly different normal parameters and cannot be compared directly
- •The presence of >15% polyphasic potentials in shoulder muscles does not automatically indicate pathology; clinicians should use full QEMG context and clinical signs to diagnose neurogenic versus myogenic disorders
- •QEMG can be a valuable objective diagnostic tool for differentiating suspected neuropathies from myopathies in sport horses with suspected neuromuscular problems
Key Findings
- •Normative QEMG values established for supraspinatus, infraspinatus, deltoideus and biceps femoris muscles in healthy Royal Dutch sport horses with specific 95% confidence intervals for duration, amplitude, phases, turns, area and size index
- •Shoulder muscles (SS and IS) showed significantly higher duration, amplitude, phases, turns, area and size index compared to hindlimb muscles (DT and BF) at P<0.01
- •Polyphasic motor unit action potentials exceeding 15% occurred in 4 of 7 normal horses in shoulder muscles, indicating this finding alone does not distinguish normal from abnormal
- •QEMG effectively discriminates between neurogenic and myogenic disorders in horses with suspected neuromuscular disease