Tonsil Trouble

Founding Medical editor Matthew Mackay-Smith, DVM, addresses an EQUUS reader's concerns about her horse's persistent cough.

Q: My 4-year-old Quarter Horse filly has a persistent cough that makes her uncomfortable and interferes with her training. After two rounds of antibiotics failed to abate the cough, our veterinarian scoped her throat, and except for an area around her epiglottis, her throat and lungs were clear. Around the epiglottis were small bumps, and a couple of them bled when there were bumped with the scope.

She was diagnosed with “follicular tonsillitis.” The only thing the veterinarian could suggest is rest. Do you have any information about this problem? Is there any other treatment than rest? Is this something that can be chronic or will it return later when training and riding season comes back around? I’ve not been able to find anything on the Internet or any of my horse books. Any information would be appreciated.

A horse coughing
Exposure to allergens, bacteria, viruses and other respiratory tract irritants may cause lymphoid tissue in a horse’s throat to enlarge and become inflamed.

A: The condition you describe is most likely lymphoid hyperplasia (also known as follicular hyperplasia, pharyngeal lymphoid hyperplasia). Horses do not have a discrete tonsil like people, but instead have small aggregates of lymphoid tissue, similar to tonsillar tissue, located throughout their throat. Exposure to allergens, bacteria, viruses and other respiratory tract irritants may cause this lymphoid tissue to enlarge and become inflamed. Lymphoid hyperplasia is characterized by upper respiratory tract inflammation, and some believe that it is also associated with as similar response in the lower respiratory tract (the lungs).

This condition is more prevalent in young horses and tends to become less of a problem with maturity. Lymphoid hyperplasia has been classified by degrees of severity (grades I-IV, with grade I being the least severe and grade IV being the most severe). From your description of the endoscopic findings, it sounds like your horse has one of the less severe forms of the disease. The grade III and grade IV forms of the disease can cause several types of clinical signs, including nasal discharge, cough, exercise intolerance and abnormal respiratory noise during exercise.

A number of treatments for lymphoid hyperplasia have been tried, but none are universally successful. The most important step in treatment is to eliminate the underlying cause, if it can be determined. The next most important step is to rest the horse for an adequate period of time to allow the inflammation to subside. This can be for as long as six to eight weeks for some horses. Other treatments include frequent administration of influenza and equine herpesvirus vaccines, use of topical and/or systemic anti-inflammatory medications, antibiotics, chemical or electrocautery, cryotherapy, and laser therapy. Your veterinarian will select therapies based on a thorough review of the horse’s medical history, a complete physical examination of the horse’s upper and lower respiratory tract and analysis of the results of appropriate ancillary diagnostic tests.

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