Q: Our 28-year-old Appaloosa, an otherwise happy, retired gelding, is suffering from what appears to be headshaking. Several months ago, he started bobbing his head in the pasture, sometimes rhythmically and sometimes in jerking, spasm-like movements. He began dragging his nose across the ground and pushing one of his pasturemates around the field, burying his head in the horse’s flank. The condition interferes with his ability to graze and, I’m sure, tires him out from the constant head movement.
His behavior was initially diagnosed by our veterinarian as photosensitization and later as photic headshaking. We were told there is no remedy for this affliction, but we could try a fly mask with ears and a nosepiece. He’d always worn a mask or a headpiece with tassels for fly control, and when we purchased an ultraviolet-blocking mask with ears, it significantly diminished his behavior. Still, though, he sporadically rubs his nose on the ground, jerks his head in spasms, and when he is really stressed, makes it clear he wants to come into his dark stall. When brought in he simmers down but doesn’t stop bobbing. We learned that the spasm behavior relates to the trigeminal nerve in his face.
We wondered if the intense sun of central Florida triggered the condition, but leaving him in his stall during the day, although diminishing the bobbing, doesn’t stop it. We also thought it might be heat related, but he continues to bob even in cool winter temperatures.
A combination of cyproheptadine, carbamazepine and acupuncture was one treatment recommendation; however if possible, I’d like to find a remedy not requiring prescription drugs. — Joan B. Collins; Eustis, Florida
A: I am sorry to hear about your horse having this difficulty. From your description, it appears to be a case of trigeminal-mediated headshaking. That is, an abnormality in the trigeminal nerve, which transmits sensation over the face, causes the horse to feel neuropathic pain, which can include burning, tingling, itching or electric-like sensations. The horse responds with a variety of behaviors, including quick jerks of the head, rubbing his nose on objects, snorting and lip licking. As in your case, it is common for the affected horse to bury his nose underneath the tail of a pasturemate and to favor shaded areas.
There are many suggested causes of headshaking, but when most of those are corrected, the horse may still show signs. It is similar to migraines in people: What causes migraines is different for each person, and treatments that are effective for one may not work for another. Triggers for headshaking include light (photic headshaking), exercise, loud sounds, smell, certain long-stem hay and other stimuli. Recent papers describe various sinus or fungal infections, but all those horses have a nasal discharge; this is obvious and uncommon as a cause.
Nevertheless, your veterinarian needs to start with a complete physical examination, which includes watching the behavior or a videotape of it, an endoscopy of the nose and airway, head radiographs and standard blood work to rule out any obvious underlying physical cause. But with most headshakers, an extensive exam will turn up no
physical abnormalities. Instead, our recent studies indicate the problem stems from a physiological abnormality in the trigeminal nerve itself that causes it to “fire” repeatedly.
Treatments that lessen or stop the signs include physical, dietary, drug and combination therapies. Physical methods include using ultraviolet-blocking masks, if sunlight is the trigger, or “nose net” devices that touch the lower part of the horse’s head and face. Chiropractic treatments and acupuncture have not been very useful in this condition to date. If the horse is too heavy, increasing exercise and modest dietary changes for weight loss may help. A number of horses respond to oral magnesium supplementation and melatonin. Consult with your veterinarian before changing a horse’s dietary regimen; magnesium supplements in particular need to be monitored to avoid potentially serious side effects.
A number of drugs have been used to control neuropathic pain, including cyproheptadine, carbamazepine and Atarax (hydroxyzine). All of these drugs also have potential side effects, so consult with your veterinarian for signs to watch for when starting the medication.
Part of the dilemma in determining what treatments are effective is that many horses will spontaneously cease headshaking at a particular time of year, and the last substance administered gets credit for the “cure.” You really need to wait a year or two to gauge the worth of a treatment. Still, we have found a great deal of success with melatonin and magnesium supplementation and, if severe enough, the use of cyproheptadine with or without carbamazepine. Another product that shows some promise is Top Stock Headshaking formula, from New Zealand; in one uncontrolled study, seven out of 10 horses improved somewhat while using this supplement, but more studies are needed to prove its effectiveness. Surgical approaches have been attempted that include cutting or sclerosing a part of the trigeminal nerve. This is not recommended by me, and I have ceased performing the procedure because of the low percentage of horses who improve and the severe pain and suffering I have observed afterward in some horses.
Because I receive so many requests for information about headshaking, I created a website, http://www.headshakerinfo.org, with information for both owners and veterinarians, including research results and assessments of various treatment options. [Note: a cyproheptadine dosage recently reported for this condition was in error (not ours), so please consult our website for additional information.] With your veterinarian’s assistance, I suspect you will find an approach that helps. Don’t give up.
I believe there is hope for the future of headshakers. Most pathology studies have found no lesions or other physical problems with the trigeminal nerve, so it must be a chemical instability that causes it to fire inappropriately. With enough research support, we may be able to identify this tweak in the trigeminal nerve and, we hope, correct it. This work may also help us gain insight into the painful condition of human trigeminal neuralgia. We are happy to accept donations to support our research into headshaking syndrome. Visit my website or contact the UC-Davis School of Veterinary Medicine for information.
John E. Madigan, DVM, DACVIM
University of California–Davis,
School of Veterinary Medicine