Ongoing Headshaking Studies
Electrophysiological evaluation of the trigeminal nerve
Following our inital findings of abnormal trigeminal nerve activity in equine headshaking (see study by Pickles and others below), we are continuing to perform further electrophysiological studies. We believe these studies are an important key to understanding the mechanism underlying headshaking syndrome.
Previous Headshaking Studies
Lack of evidence for a relationship between equine headshaking and EHV1 antigenic sequences in the trigeminal ganglia
M.A. Aleman, K.J. Pickles, G. Simonek, and J.E. Madigan, J Vet Intern Med; 2012 Jan-Feb;26(1):192-4
A cause of chronic trigeminal neuropathic pain in humans is a post-herpetic pain syndrome following reactivation of latent infection by the herpesvirus varicella-zoster (chicken pox / shingles) virus. Similarly, equine herpesvirus latency and reactivation in the trigeminal ganglion may be associated with neuropathic pain and manifest as headshaking. The aim of this study was to investigate the presence of EHV-1 in the trigeminal ganglia of healthy horses and headshaking horses.
All samples from control horses and 7 of 8 headshaking horses were negative for EHV-1. One headshaking horse tested positive for a single copy of EHV-1 gene. Therefore, this study does not support a role for EHV-1 infection and presumed postherpetic pain in the etiopathogenesis of equine headshaking.
Preliminary Investigation of somatosensory evoked potentials in equine headshaking
Pickles, K.J., Gibson, T.J., Johnson, C.B., Walsh, V., Murrell, J.C. and Madigan, J.E. (2011) Vet Record Volume 168, Issue 19, pages 511-514
Somatosensory evoked potentials (SEPs) are the electrical signals generated by the nervous system in response to sensory stimuli. These characteristic electrical signals represent the brain’s processing of noxious (harmful) stimuli in primary sensory pathways within the central nervous system. Abnormalities of trigeminal evoked potentials have been recorded in human sufferers of trigeminal neuralgia. The aim of this study was to develop a technique for investigating trigeminal nerve SEPs in control and headshaking horses.
Trigeminal SEPs were generated using this model. Headshaking horses appeared to have shorter inter-peak intervals of the SEP waveform compared to control horses, supporting abnormal trigeminal nerve physiology in equine headshaking. Further use of this model is ongoing to help clarify the neurophysiological mechanism underlying headshaking.
Use of Gonadotrophin Releasing Hormone immunisation in equine headshaking
Pickles, K.J., Berger, J., Davies, R., Roser, J. and Madigan, J.E. (2011) Vet Record Volume 168, Issue 1, pages 19-22
The aim of this study was to investigate the use of a gonadotrophin-releasing hormone (GnRH) vaccine in the treatment of headshaking in horses. Fifteen geldings received two doses of the GnRH vaccine four weeks apart. Serum was collected before and after vaccination to measure concentrations of luteinising hormone (LH) (10 horses) and follicle-stimulating hormone (FSH) (six horses). Owners recorded the frequency of seven common headshaking behaviours using a visual analogue scale (VAS) before vaccination and at two, four, eight, 12, 16 and 20 weeks after vaccination. Serum LH (P=0.008) and FSH (P=0.03) concentrations decreased significantly following vaccination. Although approximately one-third of the owners reported a subjective improvement in headshaking, serial scoring did not indicate a reduction in headshaking behaviours following vaccination with a commercial GnRH vaccine. Vaccination reactions were observed in four of 15 horses (27 per cent), including one case of severe, presumed immune-mediated, myositis.
Caudal compression of the infraorbital nerve: A novel surgical technique for treatment of idiopathic headshaking and assessment of its efficacy in 24 horses
Roberts, V.L.H., McKane, S.A., Williams, A. and Knottenbelt, D.C. (2009) Equine Veterinary Journal Volume 41, Issue 2, pages 165–170
Caudal compression of the infraorbital nerve, using platinum embolisation coils, was performed under fluoroscopic guidance. Clinical records of 24 idiopathic headshakers that had undergone this procedure were reviewed. Follow-up information was obtained by telephone questionnaire with the owner or referring veterinary surgeon. All 24 horses had at least one surgical procedure. Median follow-up time was 6 months. There were 2 horses which had surgery 2 weeks before follow-up and these were excluded from the analysis of outcome. Following one surgery, 13/22 horses (59.0%) had a successful outcome. Of the 9 horses that did not improve, surgery was repeated in 6 cases. Two of these horses had a successful outcome. Overall, a successful outcome was obtained in 16/19 horses (84.2%).
Field study of the efficacy of three types of nose net for the treatment of headshaking in horses
Mills, D.S. and Taylor, K. (2003) Veterinary Record Volume 152, Issue 2, pages 41-44
Thirty-six owners of seasonally headshaking horses took part in a trial to compare the effectiveness of three types of nose net, a traditional cylindrical net (full net) and two forms of larger mesh nets which cover only the nostrils and dorsorostral muzzle (half nets). Approximately 75% of owners reported some overall improvement with each net; around 60% recorded a 50% or greater improvement and 30% a 70% or greater improvement. The nets significantly reduced the overall headshaking score and the following specific behaviours: up-and-down headshaking, nose flipping, acting as if a bee had flown up the nose, shaking at exercise, shaking when excited, shaking in bright sunlight or in windy conditions (P<0.0001), striking at the face, shaking at night, rubbing the nose when moving, rubbing the nose on objects, sneezing, shaking in the rain and shaking indoors (P<0.05). There was no evidence of a significant effect on side-to-side headshaking, shaking at rest or rubbing the nose when stationary, but the effect on snorting was uncertain. There were few significant differences between the nets, but the half nets were reported to be significantly better at controlling ‘bee up the nose’ behaviour. Horses more than 10 years old were reportedly less likely to show a 50% or greater improvement in ‘nose flipping’ and ‘headshaking at exercise’.
Owner survey of headshaking in horses
Madigan, J.E. and Bell, S.A. (2001) Journal of the American Veterinary Medical Association Volume 219, Issue 3, pages 334-337
Owners of 109 horses with headshaking completed a survey questionnaire regarding their horse’s age, sex and breed, history, clinical signs, duration, seasonality, and response to various treatments. Seventy-eight affected horses were geldings (71%), 29 were mares (27%), and 2 were stallions (2%). Mean age of onset was 9 years. Headshaking in 64 horses had a seasonal component, and for most horses, headshaking began in spring and ceased in late summer or fall. The most common clinical signs were shaking the head in a vertical plane, acting like an insect was flying up the nostril, snorting excessively, rubbing the muzzle on objects, having an anxious expression while headshaking, worsening of clinical signs with exposure to sunlight, and improvement of clinical signs at night. Treatment with antihistamines, nonsteroidal antiinflammatory drugs, corticosteroids, antimicrobials, fly control, chiropractic, and acupuncture had limited success. Sixty-one horses had been treated with cyproheptadine; 43 had moderate to substantial improvement.
Headshaking in horses: possible aetiopathogenesis suggested by the results of diagnostic tests and several treatment regimes used in 20 cases
Newton, S.A., Knottenbelt, D.C. and Eldridge, P.R. (2000) Equine Veterinary Journal Volume 32, Issue 3, pages 208–216
Twenty mature horses with typical headshaking of 2 week-7 year duration were studied. Clinical examinations included radiography of the head and nasopharyngeal endoscopy. All were assessed at rest and at exercise, both before and after fitting an occlusive nasal mask, application of tinted contact lenses and the local anaesthesia of the infraorbital and posterior ethmoidal branches of the trigeminal nerve. Infraorbital anaesthesia had no effect in 6/7 cases but 11/17 (65%) cases showed a 90–100% improvement following posterior ethmoidal nerve anaesthesia. Tinted contact lenses had no apparent long-term benefit, although 2 cases showed a transient improvement. We found no other evidence to suggest a photic aetiology in the current series of cases. Treatment regimens based on the results of the diagnostic investigative methods included sclerosis of the posterior ethmoidal branch of the trigeminal nerve. This was effective in some cases but the benefits were temporary. Cyproheptadine alone was ineffective but the addition of carbamazepine resulted in 80–100% improvement in 80% of cases. Carbemazepine alone was effective in 88% of cases but results were unpredictable at predefined dose rates. The positive response to carbamazepine, combined with the clinical features is consistent with involvement of the trigeminal nerve, particularly the more proximal branches such as the posterior ethmoidal nerve.
Characterisation of headshaking syndrome: 31 cases
Madigan, J.E. and Bell, S.A. (1998) Equine Veterinary Journal Volume 30, Issue S27, pages 28–29
Headshaking is a condition of mature age onset with the most commonly reported clinical signs being 'flipping' of the nose, nose rubbing, snorting or sneezing, and acting like a bee is flying up the nostril. A questionnaire was completed by owners of 31 horses with headshaking syndrome. The history, time of onset, clinical presentation and treatment of this condition were reported. Headshaking appeared to be light-stimulated in approximately 60% of the horses. The condition is seasonal and recurring in the majority of horses. Treatment with cyproheptadine produced improvement of symptoms in 76% of cases. The clinical signs are suggested to be compatible with neuropathic pain producing itching, tingling or electric like sensations in the face and muzzle area of affected horses.
Photic headshaking in the horse: 7 cases
Madigan, J.E., Kortz, G., Murphy C. and Rodger, L. (1995) Equine Veterinary Journal Volume 27, Issue 4, pages 306–311
Seven horses with headshaking are described. No physical abnormalities were detected in any of the cases. Six of these horses had onset of clinical signs in the spring. The role of light was assessed by application of a blindfold or dark grey lens to the eyes, covering the eyes with a face mask and observing the horse in total darkness outdoors. Cessation of headshaking was observed with blindfolding (5/5 horses), night darkness outdoors (4/4 horses) and use of grey lenses (2/3 horses). Outdoor behaviour suggested efforts to avoid light in 4/4 cases. The photic sneeze in man is suggested as a putative mechanism for equine headshaking. Five of 7 horses had improvement with cyproheptadine treatment (0.3 mg/kg bwt b.i.d.). Headshaking developed within 2 calendar weeks of the same date for 3 consecutive years in one horse. Neuropharmacological alterations associated with photoperiod mechanisms leading to optic trigeminal summation are suggested as possible reasons for spring onset of headshaking.