Authors: Walendy Lara, Goehring Lutz Steffen, Zablotski Yury, Weyh Thomas, Matiasek Kaspar, May Anna
Journal: Journal of equine veterinary science
Summary
Transcranial magnetic stimulation (TMS) has emerged as a valuable diagnostic tool for evaluating motor pathway integrity in horses with neurological gait abnormalities, but standardised protocols have typically relied on maximum device output intensities (100%), which may cause unnecessary sensory discomfort during the procedure. Researchers subjected 36 neurologically healthy warmblood horses to TMS at varying intensities (40–100%) under sedation, recording motor potentials from all four limbs and measuring latency times (LT) and cortical motor thresholds (CMT) according to International Federation of Clinical Neurophysiology guidelines. Latency times shortened significantly with increasing stimulus intensity up to 80% of maximal output (P < 0.05), with no further improvement at 100% intensity, whilst CMT demonstrated substantial individual variation independent of body weight but showed strong linear correlation with LT across all intensity ranges (P < 0.001). These findings suggest that clinicians can reduce stimulation intensity to 80% of device output in warmblood horses whilst maintaining reliable lower motor neurone activation and reproducible recordings, thereby minimising patient discomfort without compromising diagnostic sensitivity. The established relationship between CMT and LT at submaximal intensities offers a practical pathway for standardising future TMS investigations in equine myelopathy cases, potentially improving both animal welfare and clinical utility in neurological diagnostic protocols.
Read the full abstract on PubMed
Practical Takeaways
- •Reduce TMS stimulation intensity to 80% of maximum output in warmblood horses—this achieves diagnostic accuracy while minimizing patient discomfort from sensory irritation
- •CMT assessment can be used to estimate normal latency times in individual horses at submaximal stimulation, improving diagnostic interpretation for myelopathy patients
- •Standardized TMS protocols should move away from fixed 100% intensity settings toward individualized thresholds, as inter-horse variability is substantial regardless of body size
Key Findings
- •Increasing stimulation intensities from 40% to 80% of device output significantly shortened latency times (P < 0.05), with no further significant changes at 100% intensity (P > 0.05)
- •In warmblood horses, 80% coil output stimulation intensity is sufficient for reproducible activation of lower motor neurons across all four limbs
- •Strong linear correlation exists between cortical motor thresholds (CMT) and latency times (P < 0.001) even within submaximal stimulation intensity ranges
- •Cortical motor thresholds show large inter-individual variability among horses independent of body size