Proceedings of a Workshop on - The Havemeyer Foundation

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Havemeyer Foundation Monograph Series No. 11 SALES: PROBLEMS IN THE DIAGNOSIS OF RLN – AUSTRALASIAN PERSPECTIVE B. H. Anderson Ballarat Veterinary Practice, 1410 Sturt Street, Ballarat, Victoria 3350, Australia In an ideal world treadmill video-endoscopy would be used to determine the clinical significance <strong>of</strong> varying degrees <strong>of</strong> recurrent laryngeal neuropathy (RLN) identified during post sale endoscopic examinations. This is not practical and so the less perfect procedure <strong>of</strong> resting endoscopy must be relied on. Unfortunately, this technique will not predict with 100% accuracy which horses will make a ‘whistling’ or ‘roaring’ noise at fast exercise. In New Zealand and Australia a 5-point grading system is used to help endoscopists determine the clinical significance <strong>of</strong> RLN. Grade 1 and 2 laryngeal movements are considered within normal limits. Grade 3 laryngeal movements are equivocal. Grade 4 and 5 laryngeal movements are due to clinically significant RLN (supported by a number <strong>of</strong> treadmill studies showing respiratory impairment during fast exercise in these animals). Grade 4 and 5 horses fail the post sale endoscopic examination. Horses with Grade 3 laryngeal function pass the post sale endoscopic examination. Endoscopy in these horses reveals slight laryngeal asymmetry at rest but full abduction can be achieved by the arytenoid cartilage. However, activity is generally reduced on one side (usually the left). Full bilateral abduction can be stimulated either by partial asphyxiation (nasal occlusion manoeuvre) or by inducing swallowing, but is frequently not sustained. Although some <strong>of</strong> these horses may have impaired athletic performance, recent treadmill studies (Lane 2000) indicate that in at least 75% full bilateral arytenoid abduction is maintained during fast exercise. Fortunately for endoscopists at sales within the United Kingdom a dynamic component is added to the testing procedure by using ‘wind testing’ and this aid helps improve accuracy in determining clinically significant RLN. Under this system horses with Grade 3 laryngeal movements that also make a characteristic ‘whistle or roaring noise’ when lunged at the canter, fail post sales examinations. Without the benefit <strong>of</strong> an exercise test and because the majority <strong>of</strong> Grade 3 horses have normal upper respiratory tract function at fast exercise, failing such horses in New Zealand and Australia would be very problematic. This is an area <strong>of</strong> caveat emptor and would seem to be fair to both vendors and purchasers. Using a static method to describe a dynamic process has limitations. A wide range <strong>of</strong> defective laryngeal movements exist and cut <strong>of</strong>f points can never be as precise as one would wish. Problem cases are likely. In addition, even apparently normal horses (Grade 1 or 2 laryngeal movements at rest) have been found to have abnormal laryngeal movements (Grade 3–5 or dynamic arytenoid collapse) (Kannegieter and Dore 1995; Lane 2000) and respiratory noise when galloped on the treadmill. Furthermore, it is sobering to appreciate that the progression <strong>of</strong> RLN in Thoroughbred horses to degrees which may be clinically important is estimated as 5–15%, (Anderson et al. 1997; Dixon et al. 2002). More alarming for endoscopists however is that this progression may occur quickly, over some few weeks or months. The challenge in the sales environment is to be confident that a horse can fully abduct the arytenoid cartilages. As a matter <strong>of</strong> quality control, all horses with Grade 3 laryngeal movements are examined by a second veterinarian. In horses in which laryngeal abductor function is questionable, video-endoscopic examination is made and reviewed carefully to determine that full symmetrical abduction <strong>of</strong> both cartilages is present. 45
Equine Recurrent Laryngeal Neuropathy Recently, it has come to the attention <strong>of</strong> examining veterinarians that some <strong>of</strong> the horses they are examining appear sedated. On entrance to the stall, such horses are quiet, <strong>of</strong>ten have a lower head carriage, droopy lips and may have slight protrusion <strong>of</strong> the third eyelid. The use <strong>of</strong> such drugs as acetylpromazine and valium by vendors may be the cause. It is clear from experience and documented literature that some sedative agents, notably xylazine, can reduce the range and frequency <strong>of</strong> laryngeal movements. Often horses which had normal movements (Grade 1 and 2) will develop Grade 3 laryngeal movements following sedation. While it is unlikely that Grade 4 laryngeal movements will be induced following sedation it is possible that horses with Grade 3 movements which may be borderline (ie have difficulty in achieving full arytenoid abduction) could be altered to such a degree that determining accurately if full arytenoid abduction is attained could be difficult. Veterinarians are advised that if their clients are using such agents to ‘calm’ horses in the sales environment, this may jeopardise the interpretation <strong>of</strong> laryngeal function by endoscopists. Certainly the horses most at risk are those with some degree <strong>of</strong> neuromuscular dysfunction. Presumably sedative agents work on depression <strong>of</strong> neuromuscular function. REFERENCES Anderson, B.H., Kannegieter, N.J., Goulden, B.E. (1997) Endoscopic observations on laryngeal symmetry and movements in young racing horses. N. Z. vet. J. 45, 188-192. Dixon, P.M., McGorum, B.C., Railton, D.I., Hawe, C., Tremaine, W.H., Pickles, K. and McCann, J. (2002) Clinical and endoscopic evidence <strong>of</strong> progression <strong>of</strong> 152 cases <strong>of</strong> equine recurrent laryngeal neuropathy (RLN). Equine vet. J. 34, 29-34. Kannegieter, N.J., Dore, M.L. (1995) Endoscopy <strong>of</strong> the upper respiratory tract during treadmill exercise: a clinical study <strong>of</strong> 100 horses. Aust. vet. J. 72, 101- 107. Lane, J.G. (2000) Assessment <strong>of</strong> upper airway obstruction and high-speed treadmill endoscopy. Proc. Racehorse Practice Conf. Newmarket, England, 22nd –24th June. 46
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