Thursday, August 4, 2011

Head Shaking Syndrome: Part 1 Trigeminal Nerve

Trigeminal nerve:

The term "trigeminal" comes from the Latin "trigeminus" meaning "threefold," referring to the three divisions (ophthalmic, maxillary and mandibular) of this nerve.

The trigeminal nerve functions both as the chief nerve of sensation for the face and the motor nerve controlling the muscles of mastication (chewing).

In an effort to understand what my horse is going through I'm both studying HSS and journaling Cowboy's progress and symptoms. Veterinarians have a hard time diagnosing and treating this problem because of its many varieties and possible causes. I think I've narrowed Cowboy's down to photic issues--intense sun and heat trigger, but I want to know as much about it as I can in order to figure out the best way to help him.

My first question was--what is the Trigeminal Nerve and Equine Trigeminal Neuralgia. I have to understand this to know what I'm seeing with Cowboy.

I came across a wonderful site devoted to bitless riding that discussed this nerve and how the use of bits can affect it and possibly cause HSS. Horse and Human Bitless Training and Barefoot Trimming. They wrote this about the three areas the Trigeminal Nerve can affect:

Ophthalmic branch

The ophthalmic branch of the trigeminal nerve supplies nerves to parts of the eye [the cornea, ciliary body, lacrimal gland and conjuctiva], to parts of the mucous membrane of the nasal cavity and to the skin of the eyelids, eyebrows, forehead and nose

Maxillary branch

The maxillary branch of the trigeminal nerve supplies nerves to the lower eyelid, nose, upper lip and side of the face

Mandibular branch

The mandibular branch of the trigeminal nerve supplies nerves to the mucous membranes of two thirds of the tongue, teeth and gums, skin of the temporal region, lower lip and chin, the muscles used to chew, and to some parts of the ear.

The symptoms I've seen in Cowboy today are: 1. Relief of symptoms when removed from sun, 2. Excessive yawning, 3. Hanging his head to the ground in the sun, 4. Vertical head-bobbing when standing in sun.

What I've noticed before is possible vision impairment--not blindness, but maybe some sort of distortion.

It's interesting that this also occurs in humans. Here are sketches of the human face and the Trigeminal Nerve.

Humans have reported intense pain, suicidal thoughts and double-vision.

There is a possibility that sunshine irritates Cowboy's Trigeminal nerve and causes a stinging all along the inside of his nose. Yawning and chewing might relieve some of the itchiness and discomfort.

Here are the questions I've asked myself.

1. What are the outward signs he has shown?
2. When did they start? Were there any early signs I may have overlooked?
3. How did the symptoms progress?
4. Were teeth, nose and ear issues ruled out?
5. When was he last vaccinated?
6. What things give him relief?
7. What things make him worse?
8. How have I ruled out behavioral issues?
9. What is his pain or discomfort level on a scale of 1 to 5?
10. Is he safe to handle?

I'll explain why these are important questions in Part II.


  1. Very thoughtful and thorough approach - that certainly sounds like what it is - the heat may cause some swelling that adds irritation to the nerve.

  2. Yep, I think so, too. The hardest question to answer right now is #10. I don't know how unsafe this could potentially be--say, on a ride--in the trailer--tacking up--if it were to flare up unexpectedly. I've got a lot to think's making me tired. :/

  3. Thanks for taking the time to educate us on this syndrome as you learn about it. I'm still hoping he just had a bug up his nose and he'll be back to his old self in no time.

  4. I vote for the bug up the nose, too, but then it would bother him in dark stalls. :/ HSS is on my list of things I never wanted to learn about, but now have I get older, this list gets longer. I'd say LOL, but it's more like COL (Cry Out Loud).

  5. Linda, I'm really sorry you're going through this. I hope you find a way to manage it. Is it possible to just keep a fly mask on him at all times? Except night of course. Or is it happening even with the fly mask?

    BTW - if you're tempted to get some weird looking fly mask with replaceable eyes that costs $70 and blocks 80% of UV rays - don't do it. I bought one, can't remember what it was called right now, and it's horrible. (I do have some really good 80% UV blocking material I never got around to using if you want to try making your own.)

  6. This is fascinating. Thanks for spending the time to compose all this information in your posts.


  7. Andrea--that's good to know about the masks...another thing they've used are UV blocking contacts. He doesn't want to leave his stall anymore. I made him last night, but he was head-bobbing first thing this morning and I got out there at 6:30. It goes away in the stall. I'm hoping that this is just a bad flare up and time will heal it and bring him down to a more normal base line. Honestly, I think this spells the end of our riding season..unless it improves in fall/winter. With his broken P3 injury...things aren't looking good. I'm feeling the pressure to finish with Beautiful and Cia now.

  8. Wow, this is very interesting and scary. Thank you for posting about this. I'll also be checking out that link.


Please feel welcome to join our discussion by telling us about your own thoughts and experiences.