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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Headshaking as a result of sensitization (abnormally low threshold for activation) of the trigeminal nerve, thought to cause neuropathic facial pain. A subset of horses appear to have headshaking in response to light stimulus; see chapter Photic headshaking.

Pathophysiology!!navigator!!

Sensitization of the trigeminal nerve appears to be acquired and to be the result of a functional, rather than structural, change. Cause and mechanism are unknown.

Systems Affected!!navigator!!

Neurologic—trigeminal nerve and/or central.

Genetics!!navigator!!

Unknown

Incidence/Prevalence!!navigator!!

1–4% of the UK equine population

Signalment!!navigator!!

  • Onset is usually in young adulthood (5–10 years)
  • Geldings may be overrepresented

Signs!!navigator!!

  • Predominantly vertical headshaking, often with smaller, sharp vertical head movements, and accompanied by nasal irritation (rubbing the nose, snorting)
  • At rest, but usually worse at exercise
  • Severity may be graded—0/3, no headshaking; 1/3, headshaking but not so severely as to interfere with ridden exercise; 2/3, headshaking of sufficient severity as to make ridden exercise impossible or unsafe; 3/3, headshaking even at rest
  • Some horses are only affected seasonally; if so, usually in the spring and summer

Causes!!navigator!!

Unknown

Risk Factors!!navigator!!

Unknown

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Headshaking from any other causes of facial pain, such as dental disease, temporohyoid osteopathy, iris cyst, bit and tack problems.

CBC/Biochemistry/Urinalysis!!navigator!!

N/A

Other Laboratory Tests!!navigator!!

N/A

Imaging!!navigator!!

CT of the head and endoscopy of the upper respiratory tract and guttural pouches to rule out other causes for headshaking.

Other Diagnostic Procedures!!navigator!!

  • History and observation are key. Ophthalmic and oral examinations to rule out other cause for headshaking
  • Infiltration of local anesthetic around the caudal portion of the infraorbital nerve may alleviate signs, confirming headshaking due to facial pain, although not the cause for facial pain. A negative response does not refute facial pain
  • Somatosensory-evoked potential testing under general anesthesia could confirm sensitization of the trigeminal nerves but this would not be a mainstream diagnostic test

Pathologic Findings!!navigator!!

Unremarkable

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

  • A nose net provides 70% relief in 25% of cases and is the first treatment to try. Cheap, noninvasive, and suitable for most competitions
  • Other products and supplements claim to alleviate headshaking but without scientific evidence or with scientific evidence to show they are ineffective for trigeminal-mediated headshaking

Nursing Care!!navigator!!

N/A

Activity!!navigator!!

Signs usually worse at exercise and some horses may not be safe to ride or even handle.

Diet!!navigator!!

No evidence for effect.

Client Education!!navigator!!

Headshaking may occur as a result of neuropathic pain and requires veterinary investigation.

Surgical Considerations!!navigator!!

  • There is no one good treatment for trigeminal-mediated headshaking as yet
  • EquiPENS™ neuromodulation currently has the best results with no significant side effects. Under standing sedation, the trigeminal nerve is stimulated using an electrically conductive probe. At least three procedures are required initially. If remission is attained it may only be short term with about 25% of cases showing long-term remission, although the procedure and data are still in their infancy
  • Placement of platinum coils in the nerve can alleviate signs long term in 25% of cases but with a significant risk of potentially fatal complications

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Carbamazepine and/or cyproheptadine, which have central effects, may be used although results are inconsistent and may only be short term
  • Gabapentin, used for neuropathic pain, may also be used although there are no published results
  • Pulsed high-dose corticosteroids have been shown to be ineffective

Contraindications!!navigator!!

Not for use in competition animals.

Precautions!!navigator!!

May cause side effects of drowsiness, which could have safety implications.

Possible Interactions!!navigator!!

Unknown

Alternative Drugs!!navigator!!

None with evidence of efficacy.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

None suspected.

Age-Related Factors!!navigator!!

Acquired usually in early adulthood (5–10 years). There are few longitudinal data. Some individuals may experience remission, but it is likely most remain affected and may progress.

Zoonotic Potential!!navigator!!

None

Pregnancy/Fertility/Breeding!!navigator!!

There is no evidence that these horses are at directly increased risk of having affected offspring.

Synonyms!!navigator!!

  • Headshaking
  • Idiopathic headshaking

Abbreviations!!navigator!!

CT = computed tomography

Suggested Reading ⬆ ⬇

Pickles K, Madigan J, Aleman M. Idiopathic headshaking: is it still idiopathic? Vet J 2014;201:21–30.

Roberts VL, Patel NK, Tremaine WH. 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;48(2):201–204.

Author(s) ⬆

Author: Veronica L.H. Roberts

Consulting Editor: Caroline N. Hahn