Trigeminal-mediated headshaking in horses
: prevalence, pathology, diagnosis and treatment

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


This work covers research carried out over an 11-year period (2009 – 2020), during which
my skills have developed. The research is in trigeminal-mediated headshaking, a
neuropathic facial pain condition in horses.
I have an international reputation in this field. I was awarded Fellowship of the Royal College
of Veterinary Surgeons for Meritorious Contribution to Clinical Practice, largely due to my
work in headshaking.
I am submitting seven publications, five first and two last author, for incorporation into a
thesis for a PhD by publication. Five papers have been published in Equine Veterinary
Journal, the highest impact factor equine veterinary journal. Three have been given awards,
as a result of which they have been circulated widely. One received a further award for being
in the top 10% of downloaded papers from that journal in 2019. The last author publications
were designed by me and I sourced funding and ethics approval for them. The first authors
were postgraduate students conducting their first pieces of original research and therefore
required close supervision.
Chapter One reviews current understanding of trigeminal-mediated headshaking in the
Chapter Two: Prevalence. One aspect of the impact of a condition is its prevalence. There
was no robust research into the prevalence of trigeminal-mediated headshaking in any
country. A questionnaire study of horse owners determined prevalence of headshaking to be
4.6% in the UK.
Ross SE, Murray JK, Roberts VLH (2018) ‘Prevalence of headshaking within the equine
population in the UK’ Equine Vet J. Jan;50(1):73-7.
Chapter Three: Pathology. A translational study was performed to determine whether
horses with trigeminal-mediated headshaking had focal demyelination of the trigeminal root
as do a majority of sufferers of human trigeminal neuralgia, a clinically similar syndrome. No
demyelination, and indeed no other gross pathology, was detected. This, alongside other
factors, suggests that TMH is a functional rather than structural condition, which could
therefore be reversible.
Roberts VLH, Fews D, McNamara J, Love S. (2017) Trigeminal nerve root demyelination
not seen in six horses diagnosed with trigeminal-mediated headshaking. Front Vet Sci
section Veterinary Neurology and Neurosurgery. May 15;4:72.doi:10.3389/fvets.2017.00072.
eCollection 2017.
Chapter Four: Diagnosis. Diagnosis of trigeminal-mediated headshaking is particularly
challenging as it is one of exclusion. A useful step can be to demonstrate, using diagnostic
local anaesthesia, that headshaking clinical signs are due to facial pain. A significant effect
of operator experience on the accuracy, and therefore reliability, of this technique was
Wilmink S, Warren-Smith CM, Roberts VL.H (2015) Validation of the accuracy of needle
placement as used in diagnostic local analgesia of the maxillary nerve for investigation of
trigeminally mediated headshaking in horses. Vet Rec. Feb 7;176(6):148.
Chapter Five: Treatment I. Neurectomy of the infra-orbital nerve has previously been
reported as a possible treatment for trigeminal-mediated headshaking but success rates
were low, and side-effects could be severe. A modified technique of infraorbital nerve
ablation to increase success rates and reduce side-effects was investigated. Whilst this was
achieved, only modest success rates were achieved and side effects could still be severe in
some cases.
Roberts V.L.H., McKane S.A., Williams A. and Knottenbelt D.C. (2009) Caudal compression
of the infraorbital nerve: a novel surgical technique for treatment of idiopathic headshaking
and assessment of its efficacy in 24 horses. Equine Vet J. 41(2): 165-7
Roberts V.L.H., Perkins J.D., Skärlina E., Gorvy D.A., Tremaine W.H., Williams A., McKane
S.A., White I. And Knottenbelt D.C. (2013) Caudal anaesthesia of the infraorbital nerve for
diagnosis of idiopathic headshaking and caudal compression of the infraorbital nerve for its
treatment, in 58 horses. Equine Vet J. Jan:45(1):107-10
Chapter Six: Treatment II. Development and validation of a more effective and safer
translational treatment based on a minimally-invasive therapy for people suffering
neuropathic pain. A pilot study was later expanded to a larger international, multi-centre
Roberts V.L.H., Patel N.K., Tremaine W.H. (2016) Neuromodulation using percutaneous
electrical nerve stimulation for the management of trigeminal-mediated headshaking: A safe
procedure resulting in medium-term remission in five of seven horses. Equine Vet J. 2016
Roberts VLH, Bailey M, The EquiPENS™ Group, Patel N.K. (2020) Safety and efficacy of
EquiPENS™ neuromodulation for the management of trigeminal mediated headshaking in
168 horses. Equine Vet J. Mar;52(2):238-243.
Chapter Seven discusses how my research skills have progressed and consider my
published research, its impact, and suggestions for future investigation and improvement.
Date of Award11 May 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorToby G Knowles (Supervisor) & Andrew Grist (Supervisor)


  • horse headshaking

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