Laryngeal Paralysis in Dogs Treatment

Laryngeal paralysis is a common canine, and less commonly feline, condition. Its surgical palliation though, is the subject of active ongoing research. A large number of surgical techniques have been investigated and advocated for its treatment, but so far, none have been able to replicate laryngeal function and aspiration pneumonia remains a considerable post-operative concern(1). Other than Nomura et al (2010)(2), who reported the effective restoration of bilateral cricoarytenoid function using an implantable electrical stimulator in vivo, and Greeneld et al (1988)(3) whose team used a neuromuscular pedicle ap from the rst cervical nerve to eectively reinnervate the dorsal cricoarytenoid muscle, all surgical techniques statically abduct the arytenoid cartilage. Glottic surface area is typically increased by 100 – 200%(4), depending on the technique used, to accommodate the requirement for airow during periods of increased demand.

This glottic area though, remains increased when not required, and this is particularly relevant during swallowing. Cricoarytenoid lateralization is the most widely accepted technique for the treatment of laryngeal paralysis, but thyroarytenoid lateralization, vocal fold incision or excision, arytenoidectomy and castellated laryngossure, many of these techniques having a number of modications, are also described.

Variations of the routine cricoarytenoid lateralization (“tieback”) technique involve high and low suture tension, cricoarytenoid disarticulation and transection of the sesamoid band. Bureau & Monnet (2002) showed that low suture tension increased the glottic surface area by 82%. Although high suture tension increased the glottic surface area by only 129%, this represented a 467% increase in the area that was unable to be covered by the epiglottis during swallowing(5), potentially increasing the risk of aspiration. The reported incidence of aspiration pneumonia after unilateral arytenoid lateralisation is 18 – 25%(1, 6) and the overall postoperative mortality rate is approximately 15%(1).

Recent publications have emphasized that laryngeal paralysis is a manifestation of a progressive polyneuropathy. This was demonstrated by Thieman et al (2010), who showed axonal degeneration and loss of large calibre nerve bres in the recurrent laryngeal and common peroneal nerves of aected dogs(7). In another study, only 31% of dogs with laryngeal paralysis had clinical evidence of polyneuropathy at presentation, but all cases were aected 1 year later(8). Although preoperative thoracic imaging is always recommended to detect megaoesophagus and exclude cranial mediastinal neoplasia as an aetiologic factor, Stanley et al (2010) performed positive contrast oesophagrams, and despite the absence of megaoesophagus, identied oesophageal dysfunction and correlated the degree of this dysfunction with the risk of aspiration pneumonia after lateralization(8). This potentially allows some pre-operative recognition of high-risk cases for aspiration, and more accurate prognostication. Authors of both of these articles addressed the importance of understanding, and explaining to owners, that laryngeal paralysis is a symptom of a progressive polyneuropathy, rather than an isolated condition. They emphasized the value of a thorough neurologic examination, which may include electromyography of perilaryngeal and somatic musculature, before and after surgery.

Until practical, dynamic methods of addressing laryngeal paralysis are developed, there will always be varying reports of dierent author’s approaches to what is an imperfect solution to a functional problem. A novel technique reported recently in an experimental setting ex vivo, described the placement of bilateral arytenoid nitinol stents(9), which signicantly increased glottic surface area without dramatically decreasing laryngeal resistance, and there is a possibility this approach may nd some application in the future. Although not currently used for this purpose, there may also be future application of laryngeal stenting to the treatment laryngeal collapse in brachycephalic airway syndrome.

References:
1. MacPhail CM, Monnet E. Outcome of and postoperative complications in dogs undergoing surgical treatment of laryngeal paralysis: 140 cases (1985-1998). Journal of the American Veterinary Medical Association. 2001;218(12):1949-56.
2. Nomura K, Kunibe I, Katada A, Wright CT, Huang S, Choksi Y, et al. Bilateral motion restored to the paralyzed canine larynx with implantable stimulator. Laryngoscope. 2010;120(12):2399-409.
3. Greeneld CL, Walshaw R, Kumar K, Lowrie CT, Derksen FJ. Neuromuscular pedicle graft for restoration of arytenoid abductor function in dogs with experimentally induced laryngeal hemiplegia. AMERICAN
JOURNAL OF VETERINARY RESEARCH. 1988;49(8):1360-6.
4. Pascoe JR. At the crossroads: conundrums and challenges in laryngeal surgery. Veterinary surgery : VS : the ocial journal of the American College of Veterinary Surgeons. 2007;36(6):513-4.
5. Bureau S, Monnet E. Eects of suture tension and surgical approach during unilateral arytenoid lateralization on the rima glottidis in the canine larynx. VETERINARY SURGERY. 2002;31(6):589-95.
6. Hammel SP, Hottinger HA, Novo RE. Postoperative results of unilateral arytenoid lateralization for treatment of idiopathic laryngeal paralysis in dogs: 39 cases
(1996-2002). Journal of the American Veterinary Medical Association. 2006;228(8):1215-20.
7. Thieman KM, Krahwinkel DJ, Sims MH, Shelton GD. Histopathological conrmation of polyneuropathy in 11 dogs with laryngeal paralysis. Journal of the American Animal Hospital Association. 2010;46(3):161-7.
8. Stanley BJ, Hauptman JG, Fritz MC, Rosenstein DS, Kinns J. Esophageal dysfunction in dogs with idiopathic laryngeal paralysis: a controlled cohort study. VETERINARY SURGERY. 2010;39(2):139-49.
9. Cabano NR. Eects of bilateral arytenoid cartilage stenting.