Volume 44 | Issue 1 Article 1

1982 Pharyngeal Lymphoid Hyperplasia Mary Lynn Neumeister Iowa State University

E. L. Reinertson Iowa State University

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Recommended Citation Neumeister, Mary Lynn and Reinertson, E. L. (1982) "Pharyngeal Lymphoid Hyperplasia," Iowa State University Veterinarian: Vol. 44 : Iss. 1 , Article 1. Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol44/iss1/1

This Article is brought to you for free and open access by the Journals at Iowa State University Digital Repository. It has been accepted for inclusion in Iowa State University Veterinarian by an authorized editor of Iowa State University Digital Repository. For more information, please contact [email protected]. Pharyngeal Lymphoid Hyperplasia

by Dr. Mary Lynn Neumeister* Dr. E. L. Reinertson**

Pharyngeal lymphoid hyperplasia (PLH) is slightly elevated follicular located a condition in horses involving proliferation rostrally on the ventral surface of the soft of one of the equine tonsillar structures. It has palate; been diagnosed more frequently in the past 4. The tubal tonsil being a triangular por­ few years due to a greater awareness of its ex­ tion of lymphoid tissue usually found be­ istence, a developing prevalence of en­ tween the pharyngeal openings of the doscopic examination, and/or an increased auditory tube and as solitary nodules in incidence of the syndrome. We will discuss the lateral walls of the nasopharynx and the following in this paper as they relate to the dorsal surface of the soft palate; and PLH: 5. The pharyngeal tonsil being an accumula­ 1. The age and breed predilection tion of tonsillar follicles at the caudal end 2. The equine tonsillar anatomy of the nasal septum and in the vicinity of 3. The causative agents the choanae. 4. The clinical signs and the differential Of primary concern are the tubal tonsil and diagnosis based on them the pharyngeal tonsil. These lymphoid-filled 5. The endoscopic appearance follicles on the dorsum of the are 6. The treatments of PLH. most often seen in young horses, their number In a one and a half year case load study at and size decreasing at 2 to 3 years of age, and 3 New Bolton Center,l 4,576 horses were en­ only a few being present at 4 or 5 years. This doscopically examined. Pharyngeal lymphoid age-related decrease in the amount of lymph­ hyperplasia was diagnosed in 207, or 5% of oid tissue explains the predilection of PLH for the cases. The majority of these horses were 2 to 4 year old horses. between 2 and 4 years; 95% of them were The pharyngeal tonsil is affected first when standardbreds and thoroughbreds. However, upper respiratory infections occur. This is due PLH has been found in all breeds. to 1) its common access to pathogens either There are five tonsillar structures in the inhaled from the nasopharynx or ingested horse. They are: through the oropharynx, and 2) its diffuse nature and large surface area which increases 1. The lingual tonsil consisting of follicles at the likelihood that it may be traumatized by the root of the tongue and in the area of pathogens, air turbulence, or smoke inhala­ the glossoepiglottic fold; tion. 2. The being a 2cm wide X The etiology is non-specific, including viral 10 cm long, flat, follicular tonsil on the and bacterial agents, air turbulence, and floor of the pharynx, extending caudally caustic substances. The viral agents con­ from the glossoepiglottal fold to the base sidered are Equine Herpes I (the rhino­ of the epiglottis; pneumonitis virus), Equine Herpes II (the LK 3. The tonsil of the soft palate being an oval, virus), the rhinovirus, and in the past, the 4 * Dr. Neumeister is a 1979 graduate of Iowa State parainfluenza virus. However, a consistent University College of Veterinary Medicine. clinical syndrome has not uniformly been ** Dr. Reinertson is a clinician and instructor in the Department of Veterinary Clinical Sciences, Iowa State associated with infection. 7 Irregardless, there University. is general concurrence that viral infections

4 Iowa State Veterinarian cause acute inflammation of the larynx which there is infiltration of fibrous connective may become a chronic inflammation if the tissue and the follicles appear thickened and animal's training is continued and/or secon­ fibrotic. Some may have lymphoid polyp for­ dary bacterial invasion follows. Chronicity is mation on the pharyngeal wall or in the achieved by the initial pharyngeal inflamma­ pharyngeal recess. New Bolton Center has tion causing a dcrease in the diameter of the developed a typing system used to ciassify the air passage which in turn produces a greater lymphoid proliferation, determined by negative pressure during inspiration. The number, size, appearance, and area of outcome is a downward pull on the dorsal distribution. wall of the pharynx and an elevation in the soft palate- further narrowing the pharynx. Grade 1-There are a few small, white The end result is an increased resistance, a lymphoid follicles scattered over the dor­ change in the airflow pattern, and air tur­ sal pharyngeal wall, inactive and bulence which mechanically irritates the shrunken. These are a common finding in mucosa. horses less than 4 years of age and seldom If bacterial invasion occurs, culture results affects their ventilation. in growth of Streptococcus equz" or Strepto­ Grade II - There are many small white coccus zooepz"demz"cus. These bacteria are lymphoid follicles lying close together on considered to be present as secondary in­ the dorsal and lateral pharyngeal walls. vaders only, not as the etiologic agent. Their lateral extent is the pharyngeal In the initial stages the horse is febrile and openings of the glutteral pouch or just presents with a nasal exudate. As it progresses slightly lower. Scattered among these the two most common complaints .are 1) a white follicles are a few edematous, pink, marked reduction in exercise tolerance and 2) active appearing follicles. Clinically, this noise heard on inspiration- both leading to grade may exhibit enough air resistance to an unsatisfactory record in the racing animal. cause increased air turbulence and initiate Differentials8 include a list of upper airway the development of chronic inflammatory obstructions: lesions. 1. pharyngeal lymphoid hyperplasia Grade III - Pink and white lymphoid follicles 2. epiglottal entrapment lie very close together, covering the dorsal 3. pharyngeal or subepiglottal cyst pharynx, the lateral pharyngeal walls 4. retropharyngeal cyst below the opening of the gutteral pouch, 5. gutteral pouch infections and even the dorsal surface of the soft 6. elongation or paresis of the soft palate palate. In summary, they cover all of the 7. evagination of the cricotrachealligament visible surface of the pharyngeal mucous 8. pharyngeal paralysis membrane. 9. pharyngeal foreign body Grade IV- The follicles are large and 10. tracheal collapse or stricture edematous, covering the same area as 11. neoplasms, etc. Grade III plus extending into the gutteral To distinguish between these upper airway pouches. Numerous polyps may arise from obstructions, the history should include the the pharyngeal diverticulum or the dorsal duration of the problem, the presence of odor and lateral walls. Clinical signs are usually or discharge, the severity of the signs, and the associated with Grades III and IV but oc­ time of occurrence. Physical exam includes casionally may not if the diameter of the palpation and auscultation of the pharynx; airway is sufficient to accomodate both watching and listening to the horse at work; the hyperplasia and adequate air. For this rhinolaryngoscopy; and radiographs. reason, it is important not to diagnose Endoscopy will be the most useful pharyngeal hyperplasia on endoscopic diagnostic aid. During the acute phase, the findings alone. A thorough examination, follicles will be edematous and hyperemic. especially of the respiratory and car­ Close observation reveals slight ulceration on diopulmonary systems should be done. the most prominent portion of the follicle. The accompanying nasal discharge is initially TREATMENT serous, then mucopurulent. In chronic cases, The treatment of this condition is symp-

Vol. 44, Issue No. 1 5 tomatic, the goal being the reduction in the removal of the hyperplastic tissue with number and size of lymphoid follicles. There cauterization. The choice of therapy will de­ are four regimens of treatment: 1) rest, 2) pend on the use of the animal and the medical consisting of steriods, anti­ urgency for correction of the situation. No inflammatory agents, and antibiotics, 3) one mode of therapy has consistantly pro­ cauterization using chemical, electrical, or vided favorable results. However the majority radioactive agents, and 4) immune therapy of cases undergo an age related regression of consisting of repeated vaccination with the hyperplastic lymphoid tissue as the im­ equine flu and rhinopneumonitis vaccines in mune system mature an effort to increase local immunity. Follicle development often recurs following with­ REFERENCES drawal of therapy or initiation of full work. 1. Raker, Charles, Boles, Charles L: Pharyngeal Lym­ In summary, pharyngeal follicular hyper­ phoid Hyperplasia in the Horse. Equz'ne Medz'cz'ne and Surgery, Vol. 2:202-207; April 1, 1978. plasia involves the proliferation primarily of 2. Nickel, R, Schummer, A, Seiferle, E, Sack, WO, one of the five tonsillar structures in the The Viscera of the Domestic Mammals. Verlag Paul equine. Its anatomical placement and diffuse Parey, Berlin and Hamburg, Germany, 59-60, 73-74; 1973. nature predisposes the pharyngeal tonsil to in­ 3. Raker, C. W., Diseases of the Pharynx. Modern flammation. This inflammation begins acute­ Veterinary Practice, 57(6) 396,399-400; May 1976. 4. Ditchfield, W JB, Rhinoviruses and Parainfluenza ly due to viral agents and progresses to a viruses of Horses. fA VMA 155 (164) P 384. chronic nature by the addition of air tur­ 5. Merchant, JA Packer, RA, Veterinary Bacteriology bulence and mechanical irritation, secondary and Vz'rology, 7th edition. Iowa State University Press, Ames, Iowa. bacterial invaders, and caustic agents such as 6. McAllister, Scott, Blakeslee, James R, Clinical Obser­ smoke inhalation. Clinically, the most com­ vations of Pharyngitis in the Horse. fA VMA Vol. 170 mon signs are inspiratory dyspnea and exer­ No.7. 7. Boles, CL, Epiglottic Entrapment and Follicular cise intolerance. Endoscopic exam reveals Pharyngitis; Diagnosis and Treatment. Proceedings varying grades of hyperplasia, from a few of the 21st Annual Conventz'on of the AAEP, p 31; 1975. scattered, white follicles to hyperemic, 8. Reinertson, Eric L, Iowa State University, College of edematous follicles and polyps involving the Veterinary Medicine. Personal communication, Nov. entire visible pharyngeal mucosa. The 4,1977. 9. Mitten, RW, Iowa State University, College of methods of treatment include rest, medical Veterinary Medicine. Personal communication, Jan. suppression of the inflammatory response, 11,1979. stimulation of the , and

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