Equis ISSN 2398-2977

Larynx: hemiplegia

Synonym(s): Recurrent laryngeal neuropathy, RLN, Idiopathic left laryngeal hemiplegia, Left recurrent laryngeal nerve paralysis, Roarer, Whistler, ILH

Contributor(s): Tim Brazil, Christopher Brown, Jonathan Cheetham, Paddy Dixon, Tim R C Greet, Geoff J Lane, Vetstream Ltd

Introduction

  • Recurrent laryngeal neuropathy in (commonly) young Thoroughbred, warmblood and draught horses.
  • Incidence of clinical disease about 2-6% in Thoroughbred horses (large variation reported in the literature). Up to 40% of Thoroughbred and large breeds have laryngeal asymmetry or asynchrony, not necessarily associated with clinical evidence of a functional problem.
  • Genetic/congenital etiology possible.
  • Cause: demyelination and axonal loss in the left recurrent laryngeal nerve    →   failure in the motor activity of the sole laryngeal abductor muscles   →   partial obstruction of the airway during rest or exercise   →   exercise intolerance due to hypoxia and the production of abnormal exercise-related respiratory stridor. Iatrogenic causes: perivascular injection can affect right or left sides. Other causes: brachial arch defect.
  • Signs: inspiratory noise; roar   →   whistle during exercise.
  • Diagnosis: endoscopy   Respiratory: endoscopy   resting or at exercise.
  • Treatment: surgery, eg laryngoplasty   Larynx: laryngoplasty  (technique of choice) or ventriculocordectomy   Larynx: ventriculocordectomy  .
  • Prognosis: fair to good.
Print off the Owner factsheet on Respiratory problems in your horse and Whistling and roaring to give to your clients.

Pathogenesis

Etiology

  • Chronic motor peripheral neuropathy and its high prevalence in the left recurrent laryngeal nerve may be due to the length of the nerve. Demyelination is most severe distally and is associated with axonal loss. Long central nerve degeneration, associated with RLN has been identified in the lateral cuneate nucleus but not thenucleus ambiguous.
  • Perivascular injection   →    trauma to the recurrent nerve (uncommon - can affect either side).
  • Guttural pouch mycosis   Guttural pouch: mycosis  or strangles   Strangles (Streptococcus equi infection)    →    damage to the vagal trunk (rare).
  • Organophosphate toxicity (rare).
  • Lead and other heavy metals can result in the axonopathy, but also generalized muscle weakness (rare).

Predisposing factors

General
  • Height: large horses (>16 hh) more commonly affected; rare in horses >15.2 hh.
  • Breed.
  • Sex.

Pathophysiology

  • Distal axonopathy (peripheral neuropathy): larger myelinated fibers degenerate from the motor end plate proximally   →   muscular atrophy.
  • Laryngeal adducter cricoarytenoideus lateralis (CAL), and then the sole abducter, cricoarytenoideus dorsalis (CAD) affected.

Defects of laryngeal abduction (dilation) are much more easily seen clinically and thus adducter dysfunction often goes unnoticed.

  • Degree of neurogenic myopathy correlates with the severity of clinical symptoms.
  • Normal: during fast exercise the arytenoid cartilages are held in full symmetrical abduction by the dorsal cricoarytenoid (DCA) muscle; maintained for a variable time after exercise dependent on the fitness level of the horse, the degree of exertion and the degree of pathology.
  • Abnormal: failure of DCA muscle to adequately abduct the arytenoid cartilage results in partial obstruction of the airway (rima glottidis)   →   pressure differences across the larynx increase   →   exacerbate obstruction by drawing paralyzed arytenoid and vocal cord (the Venturi effect).
  • Increased inspiratory resistance and depression of arterial oxygen tension (hypoxia) at peak inspiratory flow rates   →   respiratory noise and exercise intolerance.
  • See also Respiratory system overview   Respiratory: overview  .

Timecourse

  • Asymmetry has been reported in foals.
  • Reported increasing incidence with age.
  • Clinical signs are usually seen before the horse is 6 years old.
  • Progression variable.

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 from PubMed and VetMedResource.
  • Palumbo M I P, Moreira J J, Olivo G, Neto C R & Pyles M D (2011)Right-sided laryngeal hemiplegia and Horner's syndrome in a horse.Equine Vet Educ23(9), 448-452 VetMedResource.
  • Cramp Pet al(2009)Effect of ventriculocordectomy on upper airway noise in draught horses with recurrent laryngeal neuropathy.Equine Vet Educ41(8), 729-734 PubMed.
  • Perkins J D, Salz R O, Schumacher J, Livesey L, Piercy R J & Barakzai S Z (2009) Variability of resting endoscopic grading for assessment of recurrent laryngeal neuropathy in horses.Equine Vet J41(4), 342-346 PubMed.
  • Kim M S & Xie H (2009)Use of electroacupuncture to treat laryngeal hemiplegia in horses.Vet Rec165(20), 602-603 PubMed.
  • Cheetham J, Radcliffe C R, Ducharme N G, Sanders I, Mu L & Hermanson J W (2008)Neuroanatomy of the equine dorsal cricoarytenoid muscle: surgical implications.Equine Vet J40(1), 70-75 PubMed.
  • Hahn C (2008)Common peripheral nerve disorders in the horse.In Pract30(6), 322-329 VetMedResource.
  • Robinson Pet al(2006)Effects of unilateral laser-assisted ventriculocordectomy in horses with laryngeal hemiplegia.Equine Vet J38(6), 491-496 PubMed.
  • Robinson N E (2004)Consensus statements on equine recurrent laryngeal neuropathy: conclusions of the Havemeyer Workshop.Equine Vet Educ16(6), 333-336 VetMedResource.
  • Jansson N, Ducharme N G, Hackett R P & Mohammed H O (2000)An in vitro comparison of cordopexy, cordopexy and laryngoplasty, and laryngoplasty for treatment of equine laryngeal hemiplegia.Vet Surg29(4), 326-334 PubMed.
  • Kannegieter D B & Dore M L (1995)Endoscopy of the upper respiratory tract during treadmill exercise - a clinical study of 100 horses.Australian Vet J72, 101-107 (modern article using some of the newer techniques now available to show more light on this interesting disorder in a large number of horses) PubMed
  • Bathe A P (1993)Left laryngeal hemiplegia in the horse - a survey of diagnostic criteria and management practices employed by 20 veterinary surgeons in Europe.Equine Vet Educ5, 84-85 (a very good summary article and comparison between Europe and North America) VetMedResource.
  • Sweeney C R (1992)Left laryngeal hemiplegia in the horse: a survey of diagnostic criteria and management practices employed by 25 veterinarians in the United States.Equine Vet Educ4, 93-95 (useful overview with a North American slant) Wiley Online Library .
  • Archer R M, Lindsay W A & Duncan I D (1991)A comparison of techniques to enhance the evaluation of equine laryngeal function.Equine Vet J23(2), 104-107 PubMed.
  • Lane J G, Ellis D R & Greet T R C (1987)Observations on the examination of Thoroughbred yearlings for idiopathic laryngeal hemiplegia.Equine Vet J19(6), 531-536 (very good practical paper on the interpretation of field findings in young TB horses) PubMed.
  • Cook W R (1974)Some observations on diseases of the ear, nose and throat in the horse, and endoscopy using a flexible fiberoptic endoscope.Vet Rec6, 45-58 (an early but very readable paper from one of the most important early researchers in this field) PubMed.

Other sources of information

  • Ainsworth D M & Cheetham J (2009) Disorders of the Respiratory System.In:Equine Internal Medicine. Eds: Reed S M, Bayly W M & Sellon D C. 3rd edn. Saunders, St. Louis
  • Ducharme N (1998)Laryngeal Hemiplegia - Present Status.In:Proc World Equine Airway Symposium.


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