Equis ISSN 2398-2977

Pharynx: lymphoid hyperplasia

Synonym(s): Pharyngeal lymphoid hyperplasia

Contributor(s): Christopher Brown, Paddy Dixon, Vetstream Ltd, Rachael Conwell

Introduction

  • Proliferation of pharyngeal lymphoid tissue in young horses, previously thought to be a cause of poor performance.
  • Cause: is a normal feature of the nasopharynx in younger horses but increased size has been proposed to be a response to respiratory infection, but in studies no association found.
  • Signs: follicular tissue in the pharyngeal recess.
  • Diagnosis: endoscopy.
  • Treatment: none required.
  • Prognosis: the lymphoid tissue will reduce in size from about 5 years of age.

Pathogenesis

Etiology

  • The equine pharyngeal tonsil consists of mucosal-associated tissue, which is made up of lymphoid follicles containing B-cells and surrounded by interfollicular T-cells.
  • The nasopharynx is exposed to multiple allergens, viruses, bacteria and irritant particles, which results in response of the local lymphoid tissue to stimulate mucus-producing cells and production of local immunoglobulins.
  • Young horses are exposed to many new antigenic stimuli as a result of travel, mixing with other young horses, competition and stabling.

Predisposing factors

General
  • No association found with poor stable management, although stabling is thought to cause persistence of pharyngeal lymphoid hyperplasia in comparison with horses at pasture.
  • No association found with lower respiratory tract disease, presence of a cough or poor performance.

Specific

  • Age is the only significant risk factor for pharyngeal lymphoid hyperplasia, with lower age associated with highest prevalence (2 year old racehorses in training and 3-4 year old Sports horses).

Pathophysiology

  • Lesions are unlikely to alter gas exchange unless very severe.
  • Presence of pharyngeal lymphoid hyperplasia significantly associated with pharyngeal instability in Sports horses, as identified during overground endoscopy.
  • Pharyngeal inflammation may result in inflammation of the pharyngeal branch of the vagus nerve, leading to conditions such as dorsal displacement of the soft palate, nasopharyngeal collapse and aryepiglottic fold collapse, however this has not been proven.

Timecourse

  • Not known, but self-resolution without treatment seen with increasing age of horse.

Epidemiology

  • Young racehorses and Sports horses.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references fromPubMed andVetMedResource.
  • van Erck E (2011)Dynamic respiratory videoendoscopy in ridden sport horses: effect of head flexion, riding and airway inflammation in 129 cases.Equine Vet J43(s40), 18-24PubMed.
  • O'Neill H & Giorio M E (2010)Obstructive lesions of the equine upper respiratory tract Part 2: Surgical options and expected outcomes: Part 2.UK Vet15(5), 4-6VetMedResource.
  • Saulez M N & Gummow B (2009)Prevalence of pharyngeal, laryngeal and tracheal disorders in Thoroughbred racehorses, and effect on performance.Vet Rec165(15), 431-435PubMed.
  • Widmeret al(2009)Association of increased tracheal mucus accumulation with poor willingness to perform in show-jumpers and dressage horses.Vet J1823, 430-435PubMed.
  • Holcombe S Jet al (2006)Effect of tracheal mucus and tracheal cytology on racing performance in thoroughbred racehorses.Equine Vet J38(4) 300-304PubMed.
  • Robinson N Eet al (2006)Airway inflammation in Michigan pleasure horses: prevalence and risk factors.Equine Vet J38(4) 293-299PubMed.
  • Holcombe S Jet al(2001)Stabling is associated with airway inflammation in young Arabian horses.Equine Vet J33(3) 244-249PubMed.
  • Clarke A F & Mandelin T M (1987)The relationship of air hygiene in stables to lower airway disease and pharyngeal lymphoid hyperplasia in two groups of Thoroughbred horses.Equine Vet J19(6), 524-530PubMed(a good account of the relationship between respiratory disease and stable management).

Other sources of information

  • Holcombe S J & Ducharme N G (2007)Disorders of the nasopharynx and soft palate. In:Equine Respiratory Medicine and Surgery.Eds: McGorum B C, Dixon P M, Robinson N E & Schumacher J. Saunders Elsevier, London. pp 442-444.


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