equis - Articles
Larynx: hemiplegia
Synonym(s): Recurrent laryngeal neuropathy, RLN, Idiopathic left laryngeal hemiplegia, Left recurrent laryngeal nerve paralysis, Roarer, Whistler, ILH
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.
Presenting signs
- Respiratory noise during exercise; initially inspiratory, later expiratory also.
- Exercise intolerance.
- Poor performance.
- Changed vocalization (dysphonia) - may be associated with previous laryngeal surgery.
Age predisposition
- 2-3 year old Thoroughbreds.
- 4-5 year old in Steeplechasers.
Breed/Species predisposition
- Thoroughbreds Thoroughbred .
- Warmbloods Dutch warmblood .
- Draught horses Irish Draught .
Cost considerations
- Surgical costs - vary depending on techniques.
- Loss of training time and athletic ability can be costly.
- Diagnostic evaluation is moderately expensive.
Special risks
- Anesthesia Anesthesia: general - overview .
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.
- 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: 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 et al (2011) Right-sided laryngeal hemiplegia and Horner's syndrome in a horse. Equine Vet Educ 23 (9), 448-452 VetMedResource.
- Cramp P et al (2009) Effect of ventriculocordectomy on upper airway noise in draught horses with recurrent laryngeal neuropathy. Equine Vet Educ 41 (8), 729-734 PubMed.
- Perkins J D, Salz R O, Schumacher J et al (2009) Variability of resting endoscopic grading for assessment of recurrent laryngeal neuropathy in horses. Equine Vet J 41 (4), 342-346 PubMed.
- Kim M S & Xie H (2009) Use of electroacupuncture to treat laryngeal hemiplegia in horses. Vet Rec 165 (20), 602-603 PubMed.
- Cheetham J, Radcliffe C R, Ducharme N G et al (2008) Neuroanatomy of the equine dorsal cricoarytenoid muscle: surgical implications. Equine Vet J 40 (1), 70-75 PubMed.
- Hahn C (2008) Common peripheral nerve disorders in the horse. In Pract 30 (6), 322-329 VetMedResource.
- Robinson P et al (2006) Effects of unilateral laser-assisted ventriculocordectomy in horses with laryngeal hemiplegia. Equine Vet J 38 (6), 491-496 PubMed.
- Robinson N E (2004) Consensus statements on equine recurrent laryngeal neuropathy: conclusions of the Havemeyer Workshop. Equine Vet Educ 16 (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 Surg 29 (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 J 72, 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 Educ 5, 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 Educ 4, 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 J 23 (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 J 19 (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 Rec 6, 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, USA.
- Ducharme N (1998) Laryngeal Hemiplegia - Present Status. In: Proc World Equine Airway Symposium.