Abnormal locomotor muscle recruitment activity is present in horses with shivering and Purkinje cell distal axonopathy.
Authors: Aman J E, Valberg S J, Elangovan N, Nicholson A, Lewis S S, Konczak J
Journal: Equine veterinary journal
Summary
# Editorial Summary Shivering in horses involves disordered cerebellar control of hindlimb movement, yet the precise muscular manifestations of this neurological condition have remained poorly characterised. Aman et al. (2018) recorded surface electromyographic activity from key hindlimb muscles (biceps femoris, vastus lateralis, tensor fasciae latae and extensor digitorum longus) in seven affected draught horses and six controls during forward walking, backward walking and trotting, whilst simultaneously examining deep cerebellar nuclei tissue for pathological changes. Shivering horses demonstrated markedly abnormal muscle recruitment patterns particularly during backward locomotion—biceps femoris and vastus lateralis showed significantly elevated amplitudes (88.5% and higher peak activity respectively) that resembled trotting intensities rather than the controlled, reduced muscle activation seen in healthy backward walkers, with deficits present across at least 25% of the stride cycle in all cases. Immunohistochemistry revealed characteristic calbindin-positive spheroids within degenerating Purkinje axons in all examined shivering horses, establishing a direct neuroanatomical correlate, and notably, clinical locomotor exam scores correlated strongly with electromyographic findings (r = 0.87). For practitioners, these findings provide objective evidence that shivering reflects a discrete cerebellar neuropathy affecting motor control circuits, suggesting that gait assessment under backward locomotion conditions may offer diagnostic value, and that the severity of muscle dyscoordination directly reflects underlying neuronal damage rather than representing a primary muscular or biomechanical problem.
Read the full abstract on PubMed
Practical Takeaways
- •Shivering is a neurological disorder characterized by abnormal muscle activation patterns, particularly evident during backward movement; backward walking assessment may aid clinical diagnosis
- •The identification of Purkinje cell degeneration provides a pathological basis for understanding shivering and may inform future therapeutic approaches targeting cerebellar dysfunction
- •Electromyography can objectively quantify the severity of abnormal muscle recruitment in shivering horses and may be useful for monitoring disease progression or treatment response
Key Findings
- •Shivering horses showed significantly elevated sEMG amplitude during backward walking (88.5±21.5%) compared to forward walking (49.2±8.9%), unlike control horses where backward and forward walking were similar
- •Biceps femoris and vastus lateralis muscles displayed abnormally elevated recruitment in all seven shivering horses during backward walking, falling outside two standard deviations of control values for ≥25% of stride
- •Calbindin-positive spheroids indicative of Purkinje cell axonal degeneration were present in deep cerebellar nuclei of all six shivering horses examined
- •Strong correlation found between clinical locomotor exam scores and both peak EMG (r=0.87) and integrated EMG (r=0.87) activity