What is the larynx?
The larynx is a structure that divides the trachea (windpipe) and the esophagus (tube leading to the stomach. The larynx consists of muscles and small cartilaginous structures (The larynx is important during breathing, vocalizing (neighing), and swallowing. The larynx can be palpated externally in the horse’s throat latch region. The larynx is located where the pharynx (Back of the horse’s throat) divides into the trachea and esophagus, and connects the nasal passage to the windpipe (trachea).
Image retrieved from http://www.thehorse.com/free-reports/29997/equine-upper-airway
Normal larynx of a horse; arrows point to the arytenoid cartilages. (Left arrow points to the right arytenoid cartilage of the horse, right arrow points to the left arytenoid cartilage. This image retrieved from https://www.acvs.org/large-animal/laryngeal-hemiplegia
What is Laryngeal Hemiplegia?
Laryngeal Hemiplegia is caused by the paralysis of either the left or right muscle which controls the arytenoid cartilage. The paralysis is due to nerve loss (innervation) to a muscle on the left or right side of the throat. This muscle is responsible for pulling left arytenoid open during inspiration (when the horse breathes in). The left arytenoid cartilage is affected 95% of the time. Frequently there is a progressive loss of function. The hemiplegia may begin with the left side of the larynx is slower than the right, and can progress to complete paralysis. This is the origin of one of the syndromes names; Hemi (one side) plegia (paralysis). Horses with laryngeal hemiplegia are also called “Roarers” or “Flappers” as they have a loud roaring noise when working. The loud noise is due to the left arytenoid drooping into the airway or glottis. The affected arytenoid vibrates as the horse inhales resulting in the roaring noise. This syndrome commonly occurs in Thoroughbreds, however other breeds such as Warmbloods, Draft horses, Standardbreds, and Quarter Horses. The American college of Veterinary Surgeons report that “roaring” is commonly seen in male horses greater than 15 hands.
What are the signs and symptoms?
The American College of Veterinary Surgeons report the following findings –
- Usually seen in horses between 3–7 years’ old
- exercise intolerance that has gotten worse over weeks to months
- classic “whistling” or “roaring” noise heard during exercise (usually while cantering or higher activity)
- sound of the horse’s whinny may change
- gasping for breath after exercise
- Muscle atrophy (or shrinking) at the throat latch
How can Laryngeal Hemiplegia be diagnosed?
The Arizona Equine veterinarians utilize video endoscopy to examine the airway. The hemiplegia is graded on a scale from 1 to 4, with 4 being the most severe. Endoscopy is a diagnostic tool that allows our veterinarians to examine some body cavities that are inaccessible otherwise. To accomplish these examinations, Arizona Equine uses videoendoscopy. This is a type of endoscope that has a camera chip at the end of a long, narrow tube (about ½ inch in diameter). The advantage of a videoendoscope as compared to a regular endoscope is that a videoendoscope allows the image to be seen on a monitor (TV screen) as the examination is being done, allowing anyone in the room to see what the veterinarian is seeing. A regular (non-video) endoscope projects images onto a small eyepiece that can be viewed by one person at a time. A videoendoscope also allows us to print out pictures for the owner to take home, or to be sent to the referring veterinarian.
Videoendoscopic images – the upper left image is grade 1, upper right grade 2, lower left grade 3, and lower right grade 4 images
What is the treatment?
There are 4 treatment options, as described below: prosthetic laryngoplasty (a “tie-back surgery”), ventriculectomy +/- cordectomy, arytenoidectomy, and neuromuscular pedicle graft.
- Prosthetic Laryngoplasty: Most common treatment; requires general anesthesia. The paralyzed cartilage is “tied back” into an open/abducted position through an incision in the throat latch area. This procedure is successful approximately 70-90% of the time, the horse’s “job” directly impacts success.
- Ventriculectomy/Cordectomy: The ventricle and the vocal cord (located under the arytenoid cartilage) is removed to widen the airway that is performed alone or along with a prosthetic laryngoplasty (Figure 4). A laser is utilized and passed through an endoscope (or “scope”) up the nostril. Laser techniques are done with your horse awake and standing. No incision is necessary with the laser technique since the endoscope and laser are passed up the nose to the larynx. This technique is 20 – 30% effective when performed alone.
- Arytenoidectomy: The removal of the paralyzed arytenoid cartilage which enlarges the opening to the trachea. Not the first treatment of choice; reserved for horses that have had a failed tieback or horses with an infected arytenoid cartilage. Requires general anesthesia, done through an incision into the throat (called a laryngotomy; see Ventriculectomy/Cordectomy). Increased risk of complications and decreased prognosis for returning to the previous level of competition vs. prosthetic laryngoplasty.
Horse with grade 4 paralysis pre-operatively (left: arrow points to a Grade 4, completely paralyzed arytenoid cartilage) and post-operatively after a tieback and ventriculocordectomy (right: star on ventriculocordectomy site (removal of the ventricle and vocal fold). Image retrieved from https://www.acvs.org/large-animal/laryngeal-hemiplegia
About the author
Dr. Gayle Leith is a 1988 Wisconsin graduate, has a M.S. in Reproductive Physiology and is interested in medicine, lameness, and theriogenology. She has been with Arizona Equine since 1988. Arizona Equine Medical & Surgical Centre offers a range of equine diagnostic and treatment services at this facility in Gilbert, Arizona. .As the largest center of its kind in the desert southwest region we offer ultrasonography, nuclear scintigraphy, MRI, endoscopy and computed and digital radiology. The surgical facilities are equally extensive and include arthroscopy, colic surgery, laser surgery, laparoscopy and many types of soft tissue surgery. Dr. Gayle Leith is a boarded member of the American Board of Veterinary Practitioners – Certified in Equine Practice. Dr. Leith first became boarded in 1995, she successfully recertified in 2005 and 2015. She is certified until 2025. The American Board of Veterinary Practitioners members must re-certify every 10 years to maintain their diplomate status. ABVP certifies veterinary practitioners with exceptional knowledge, skill, and competency in the care of the total patient. The ABVP board certified veterinarian has demonstrated they are capable of providing a high level of clinical practice. Dr. Leith’s hobbies include spending time with her family, showing horses she has raised and trained in the amateur hunter divisions, oil painting, traveling, and target shooting.