Q: I have an 8-year-old Thoroughbred mare that was diagnosed with arytenoid chondritis. The attending vet was shocked that the mare wasn't panicking due to not being able to breathe--both arytenoid cartilages were almost completely collapsed into her airway. She was treated with daily SMZs (sulfamethoxazole, an antibiotic) for a month, as well as a throat spray of Furacin and DMSO (dimethyl sulfoxide). Now my mare appears to be better, but I can still hear her breathing loudly on a few occasions. However, she doesn't appear to be struggling for air like she had before she was treated.

She seems most affected when the weather is warm and sunny. I have managed her on 24/7 turnout with access to a run-in shed and in a stall with an attached run with more than 10 hours of daily turnout and see no difference in her preferring one over the other. I was told this condition is a form of "roaring" (laryngeal hemiplegia, a condition involving larynx dysfunction that can severely compromise a horse's ability to breathe, especially during exercise) but I can't find any information on this specific problem or what her prognosis is for returning to work in dressage, hunters, or possibly low-level eventing. I have not exercised her since this diagnosis, mostly due to my time restrictions and the winter weather.

What causes arytenoid chondritis, and is it curable? Are there any management changes I can make to keep her comfortable? Would she be able to be a broodmare? Is this condition hereditary?

via e-mail

A: Arytenoid chondritis (arytenoid chondropathy) is an uncommon acquired condition of the horse's larynx (voice box) that leads to airway obstruction, most commonly diagnosed in young racehorses (two to four years old). It also affects nonracehorses, but usually later in life. Typically, the condition is severe and advanced when it is identified in mature nonracehorses.

Arytenoid chondritis is likely not heritable. There are few satisfactory explanations for why horses develop arytenoid chondritis, although it is believed to result primarily from injury to overlying mucosal tissue (which normally protects the cartilage) with secondary bacterial infection. In some cases chondritis may occur as a complication of previous laryngeal surgery or injury. In mature horses that are not being subjected to rigorous exercise, the disease process often leads to an insidious and gradual growth of large granulomas (areas of infection due to tissue injury or infection) that obstruct the laryngeal airway. These horses presumably adapt to or compensate for the presence of the mass (by preferring not to exercise) and may not exhibit noticeable signs of obstruction until they undertake significant exercise (spontaneously or when being ridden).

Eventually the enlarging granuloma causes significant obstruction, even at rest, and the horse will manifest severe and sudden evidence of respiratory embarrassment (i.e., struggling to breathe, insufficient oxygenation of the blood, weakness, distress). The size of the obstructing granuloma can be remarkable in these cases when viewed through an endoscope (one might wonder how such a large abnormality could have been present with the horse showing no signs of difficulty breathing).

Arytenoid chondritis lesions identified in racehorses are usually less severe: Affected racehorses begin to exhibit diminished performance, cough when exerted, and make abnormal noise during exercise (similar to "roaring").

Unfortunately, a "cure" does not exist for arytenoid chondritis. Early, mild cases may respond to medical treatment (as you have noted in your question), but antibiotics are notoriously ineffective for resolving infection inside a cartilage structure. In advanced and severe cases (such as you have described), it is likely that permanent structural degradation has occurred that will interfere with the normal function of the mare's larynx for the remainder of her life (preventing her from being athletic). Untreated, the granuloma likely will occlude the mare's airway completely and lead to her death.

There are two surgical treatments that should be considered for this mare: surgical removal of affected cartilages from the larynx (partial arytenoidectomy) or tracheostomy (a surgical opening into the wind-pipe to provide an alternative airway and relieve the obstruction). The decision as to the best surgical treatment option for your mare should be based on consultation with a surgery specialist, results of endoscopic evaluation, and radiographs of the larynx.

We have performed tracheostomy on several similarly affected (mature) female horses that have gone on to become successful broodmares.

About the Author

Phillip Johnson, BVSc (Hon), MS, Dipl. ACVIM

Philip J. Johnson, BVSc (Hons), MS, Dipl. ACVIM, Dipl. ECEIM, MRCVS is Professor of Equine Medicine and Surgery at the University of Missouri College of Veterinary Medicine

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