Merck Manual

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Pet Owner Version

Pharyngeal Lymphoid Hyperplasia (Pharyngitis) in Horses


Bonnie R. Rush

, DVM, MS, DACVIM, Equine Internal Medicine, College of Veterinary Medicine, Kansas State University

Reviewed/Revised May 2019 | Modified Oct 2022

Pharyngeal lymphoid hyperplasia is a condition that occurs in young horses (1 to 3 years old). Unlike humans, horses do not have masses of lymphoid tissue that make up tonsils. Instead, there are follicles of this tissue spread over the pharynx. The follicles blend with normal mucosal tissue as the horse ages, but they are prominent in younger horses. Overgrowth (hyperplasia) may occur. While it was previously thought that the overgrowth was a cause of poor performance in younger horses, it is now thought to be of little significance in most cases. Occasionally these follicles may appear inflamed and produce a discharge that contains mucus or pus; this is likely the result of a mild viral infection, and treatment is usually not needed. Rest and nonsteroidal anti-inflammatory drugs can be used for horses showing signs of pain such as reduced appetite and frequent swallowing.

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