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Home / Equine Research Bank / Equine Vet J / Motor pathway evaluation by transcranial magnetic stimulatio...
Equine veterinary journal2025; doi: 10.1111/evj.14506

Motor pathway evaluation by transcranial magnetic stimulation in Swedish horses with acquired equine polyneuropathy.

Abstract: Acquired equine polyneuropathy in Nordic horses (AEP) is the most prevalent equine polyneuropathy in Norway, Sweden, and Finland and is characterised by pelvic limb knuckling due to metatarsophalangeal extension dysfunction. Objective: To evaluate the function of descending motor pathways in AEP using transcranial magnetic stimulation (TMS). Methods: An analytical, observational cohort design. Methods: Clinical findings and TMS results of 20 horses from an AEP outbreak in Sweden were evaluated at 5-month intervals. Latency time (LT) in milliseconds (ms) between coil discharge and onset of muscle potential was recorded for thoracic and pelvic limbs. Results: Fourteen affected horses showed knuckling, 2 horses showed lameness, and 6 horses were neurologically sound and showed no clinical signs at the first visit. Thirteen of 14 neurologically affected horses had improved clinically 5 months later, four no longer showed knuckling. Motor neurological dysfunction with increased LT was confirmed by TMS in all 14 affected horses at both visits. Mean difference in LT from normalised reference values (ΔLT) in the pelvic limbs of affected horses was +12.95 ms (+38%) at the first examination (1.9-29.6 ms; SD 1.23; n = 14), and +8.1 ms (+24%) 5 months later (1.0-18.9 ms; SD 1.21; n = 14), cutoff >0.8 ms. Eleven of 14 affected horses also presented delayed TMS responses in the thoracic limbs, with up to 14% ΔLT increase. Neurologically sound, non-lame horses (n = 8) showed mean ΔLT -0.5 ms (-1.8 to 0.2 ms; SD = 0.64) in pelvic, and -0.35 ms (range, -0.7 to 0 ms; SD = 0.26; n = 8) in thoracic limbs, cutoff >0.2 ms. Conclusions: Examinations were only repeated once. Conclusions: This study confirms the involvement of motor pathways in AEP and adds to the previously established involvement of sensory nerve fibres. Sensory and motor involvement contributes to the mismatch of ascending and descending nerve signals and to the clinical manifestations. TMS may be useful in evaluating clinical and subclinical cases of AEP.
© 2025 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2025-04-21 PubMed ID: 40257381DOI: 10.1111/evj.14506Google Scholar: Lookup
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Summary

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This study investigates the function of motor pathways in horses affected by Acquired Equine Polyneuropathy (AEP), a condition prevalent in the Nordic region. It uses Transcranial Magnetic Stimulation (TMS) to analyze 20 horses from an outbreak in Sweden.

Research Methodology

  • This study undertakes an analytic, observational cohort design.
  • The researchers conducted clinical examinations and TMS assessments on 20 horses affected by an AEP outbreak over a period of five months.
  • They utilized TMS to measure the latency time (LT) between the coil discharge and the onset of the potential muscular response within the horses.
  • The study evaluated these readings in both thoracic and pelvic limbs.

Results

  • Of the 20 horses evaluated, 14 demonstrated signs of knuckling, 2 showed lameness, and 6 showed no clinical signs at the initial visit.
  • After five months, 13 of the 14 horses affected neurologically showed clinical improvements, with 4 no longer showing signs of knuckling.
  • All 14 neurologically affected horses, however, exhibited increased LT confirmed by TMS in both visits.
  • There was an increase of 38% in LT in the initial examination and 24% in the follow-up examination for the affected horses’ pelvic limbs.
  • Eleven of the 14 affected horses also showed delayed TMS responses in their thoracic limbs, with up to 14% ΔLT increase.
  • The neurologically sound horses, who demonstrated no lameness or clinical signs, showed minuscule variations in their LT response.

Conclusions

  • The study confirmed the involvement of motor pathways in AEP.
  • This research adds to the existing knowledge about the involvement of sensor nerve fibers, indicating a discrepancy in the transmission of ascending and descending nerve signals, which contributes to the observed clinical symptoms in AEP.
  • The use of TMS can be valuable in evaluating clinical and subclinical cases of AEP.

Cite This Article

APA
May A, Hanche-Olsen S, Goehring LS, Matiasek K, Jäderlund KH, Zablotski Y, Gröndahl G. (2025). Motor pathway evaluation by transcranial magnetic stimulation in Swedish horses with acquired equine polyneuropathy. Equine Vet J. https://doi.org/10.1111/evj.14506

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English

Researcher Affiliations

May, Anna
  • Equine Clinic, Centre for Clinical Veterinary Medicine, Ludwig Maximilians University, Munich, Germany.
Hanche-Olsen, Siv
  • Department of Companion Animal Clinical Sciences, Norwegian University of Life Sciences, Ås, Norway.
Goehring, Lutz S
  • Gluck Equine Research Center, University of Kentucky, Lexington, Kentucky, USA.
Matiasek, Kaspar
  • Section of Clinical & Comparative Neuropathology, Centre for Clinical Veterinary Medicine, Ludwig Maximilians University, Munich, Germany.
Jäderlund, Karin Hultin
  • Department of Companion Animal Clinical Sciences, Norwegian University of Life Sciences, Ås, Norway.
Zablotski, Yury
  • Clinic for Ruminants, Centre for Clinical Veterinary Medicine, Ludwig Maximilians University, Munich, Germany.
Gröndahl, Gittan
  • Department of Animal Health and Antimicrobial Strategies, Swedish Veterinary Agency, Uppsala, Sweden.

Grant Funding

  • Swedish Association for the Protection of Animals (Svenska Djurskyddsfu00f6reningen)

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