Pharyngeal Lymphoid Hyperplasia in Horses

Pharyngeal lymphoid hyperplasia (PLH) is a common condition seen in young horses. Horses don’t have tonsils but rather have many follicles of lymphoid tissue that grow over the roof and wall of the pharynx. These follicles may become inflamed and excrete mucoid. Most horses go through this condition as it seems to be a normal immunological event. It may lead to discomfort for your horse such as pain and labored breathing, and in this case, veterinary care should be sought out.

Pharyngeal lymphoid hyperplasia is inflammation of the dorsal pharyngeal wall in younger horses and can cause difficulty in swallowing.

Horses do not have the same type of tonsil like humans, but instead, have clusters of lymphoid tissue at the rear of their throat.

• Your horse may have difficulty swallowing depending on the severity of the pain
• A persistent cough that unsettles your horse
• Your horse may appear depressed 
• Follicular tissue inflammation
• Nasal discharge in some cases
• Lack of appetite 

Types 

• Characterised by inflammation of the upper respiratory tract in your horse
• PLH is graded by the degree of severity that the symptoms cause, classified as Grades 1, 2, 3, and 4
• Grade 1 is the least severe with minor effect on your horse
• Grade 4 the most severe causing pain and discomfort
• Grades 3 and 4 have nasal discharge 
• Prevalent in younger horses

It is not really known what triggers this condition, but your horse will grow out of it as it matures. It seems to be an immunity conditioning reflex.

• Maybe caused by dust and pollen irritants in your young horse
• Exposure to allergens that may be natural or chemical in nature 
• Bacterial infection or virus
• Usually self-healing in most minor cases

If you are concerned with your horse’s breathing or difficulty in swallowing, you should call on your veterinarian to check his condition. The veterinarian will do a physical exam of your horse, checking the throat and respiratory system. Using an endoscopy will allow a clearer picture of what is happening and what the cause of the difficulty in swallowing is. Samples from a gentle scraping of your horse’s throat can be analysed to see what is causing the problem, which can then be acted upon to treat the condition. Severe forms of PLH cause problems for your horse when exercising, and therefore, your horse may show an intolerance towards any activity. Respecting your horse and allowing time off for healing will greatly benefit the recovery time. If the condition is the grade 3 or 4 type, your horse’s breathing may sound loud or labored during exercise. 

In order to further investigate the cause for the labored breathing, your veterinarian may choose to perform additional imaging tests such as x-ray or ultrasound to rule out an obstruction or guttural pouch disorders. If the veterinarian feels neoplasia is a possibility, he may want to have a biopsy done.

Normally simple cases of this condition are self-healing and usually not considered a health problem but rather part of your horse’s natural development of their immune system. Systemic and inhaled corticosteroids may assist healing and help your horse through a difficult time. Once pharyngeal lymphoid hyperplasia in your horse reaches the Grade 3 or 4 stage, it is critical to get help from your veterinarian to assist your horse to heal. This condition requires frequent administration of vaccines targeted at influenza or equine herpesvirus. Your veterinarian may also use topical anti-inflammatories, antibiotics, and perhaps even laser therapy depending on the severity of the condition. A complete examination of your horse’s upper and lower respiratory tract with analysis of the results will provide information needed to continue the treatment. Resting your horse will aid recovery along with clean bedding and water, and clean pasture to graze in.

This condition is usually easy to manage and may self-heal. On the occasion where it is severe, the treatment (medication) may need to continue for several weeks. As your young horse matures, he will usually grow out of this type of ailment as he develops his immune system to cope. As is normal in all health issues, rest and allowing time for the body to recover is the best option. Turning your horse out to graze and rest will usually be all that is required. For severe cases, ongoing veterinary treatment may be required in the case of medications and keeping close observation of how your horse is reacting to the medication.