It is that time of the year when we are close to seeing warmer days. Soon, we can expect our canine patients to be out and about enjoying summer—hiking, swimming, and playing at the dog park. It is also the time of year when we see increased cases of non-brachycephalic patients present in an emergency or referred to the surgical department for weakness, exercise intolerance, respiratory distress, and decreased tolerance for activity in warm climate. Unlike the typical brachycephalic breeds commonly presenting respiratory issues during warmer weather, this population consists of older dogs, mainly retriever breeds. Although these non-brachycephalic patients can present urgently with respiratory distress, thorough questioning will often reveal slowly progressive exercise intolerance, coughing, change in the character of voice, and mobility concerns. “Dalmatians can be affected by congenital laryngeal paralysis, which can manifest as a systemic neuromuscular disorder causing head tremors, hind limb weakness, ataxia, and inspiratory dyspnea.” Anatomy The larynx is the cartilaginous opening of the trachea and sits just caudal to the base of the tongue and soft palate. It consists of the epiglottis and paired thyroid, cricoid, sesamoid, and arytenoid cartilages. Under normal conditions, the cricoarytenoid dorsal muscles abduct (open) the arytenoids during inspiration to allow air movement through the larynx. The cranial and caudal nerves branch from the vagus nerve to innervate the larynx. The larynx has three functions: closure of the rima glottis via the epiglottis during swallowing, decreasing airway resistance during inspiration, and voice production via the vocal cords.1 With laryngeal paralysis, the arytenoid cartilages fail to abduct (open) the arytenoids during inspiration and fail to adduct (fully close) to protect the esophagus during swallowing. Two forms of laryngeal paralysis are common: congenital and acquired. Congenital laryngeal paralysis has been reported in several breeds, including malamute, Dalmatian, Rottweiler, and Bouvier des Flandres. Many affected dogs will present with clinical signs before one year of age. Some severely affected dogs are symptomatic at birth.2 Laryngeal paralysis often manifests as systemic neuromuscular disease, including head tremors, hind limb weakness, ataxia, and inspiratory dyspnea. The disease is progressive and carries a poor prognosis. Acquired laryngeal paralysis may be caused by trauma, chronic endocrine disorders, infection, toxicity or idiopathy. Idiopathic laryngeal paralysis is the most common form, although genetic variants in affected dogs have been identified.3,4 This form of laryngeal paralysis is seen mostly in older retrievers, Saint Bernards, and Irish setters. Sixty percent of cases are Labradors,5 with most patients 10-11 years of age at presentation.5,6 Diagnosis Patients with acquired laryngeal paralysis present with a variety of clinical signs, some related primarily to respiratory dysfunction and others related to systemic neurologic. Common symptoms at the time of presentation are gagging or choking, especially after eating or drinking (28 percent), change in character of voice (56 percent), and noisy respiration.7 These dogs will progress to activity intolerance. This progression may be slower, taking months to become noticeable. During the warmer and more humid times of year, these dogs will often present in respiratory distress. A thorough workup for a patient with suspected laryngeal paralysis should include a thorough physical examination, neurologic exam, complete blood count and biochemical panel, thyroid hormone testing, thoracic and neck radiographs, and sedated airway exam. Basic laboratory testing may identify possible thyroid dysfunction, aspiration pneumonia, or other non-specific changes. Radiographs help look for underlying pathology or other causes of activity intolerance (neoplasia in the mediastinum, neck) or concurrent diseases, such as aspiration pneumonia, megaesophagus, and/or pulmonary edema, The incidence of concurrent megaesophagus is 11 percent,1 with a larger number of patients likely having esophageal dysfunction that is sub-clinical early in the course of the disease.7 This is important to identify as megaesophagus has been associated with increased complications associated with laryngeal paralysis. Megaesophagus may first be noted in the cervical or cranial thoracic esophagus.7 Sedated airway exam is critical to confirm the diagnosis of laryngeal paralysis, confirm unilateral vs. bilateral involvement, rule out masses or other obstructive lesions (laryngeal collapse, elongated soft palate, etc.). Anesthetics and sedative medications can all affect laryngeal function. Doxapram can be administered if laryngeal motion is absent. This stimulant will increase respiratory rate and tidal volume but can also cause paradoxical motion of the arytenoid cartilages. An unaffected patient should have equal and symmetrical opening of both arytenoid cartilages during inspiration. Patients with laryngeal paralysis often have arytenoid cartilages with minimal movement or “fluttering” during respiration. Treatment Cases presented on an emergency basis should be stabilized with sedatives, a cool environment, and supplemental oxygen. If present, heat stroke and its sequelae should be identified and treated. Nonsurgical treatment. Medical management of laryngeal paralysis involves environmental management to prevent excitement and overexertion, sedation, and anti-anxiety medications. Anecdotally, some veterinarians have promoted the use of doxepin, a tricyclic antidepressant and antihistamine, in patients with laryngeal paralysis.7 A study by Rishnew et al. found no measurable improvement in clinical signs of laryngeal paralysis in Labrador retrievers with this medication.8 Surgery. Although several surgical techniques have been described, arytenoid lateralization remains the preferred surgical treatment for most affected dogs. Arytenoid lateralization (tie-back) is performed unilaterally, even in bilaterally affected dogs. A higher complication rate is seen with a bilateral procedure.1 This technique involves placing one or two sutures between the cricoid cartilage and the muscular process of the arytenoid cartilage. Sutures can also be placed between the thyroid cartilage and the arytenoid cartilage to encourage lateral and not caudal displacement of the cartilages.1 These cartilages can be brittle in geriatric patients, making suture holding difficult. An appropriate amount of abduction must be achieved to relieve the clinical signs related to the airway without excessive abduction that may increase the risk of aspiration. This is often accomplished by extubating the patient and observing the larynx by an assistant in the operating room, with reintubation while the rest of the procedure is completed. Ninety percent of animals undergoing arytenoid lateralization should have improvement in clinical symptoms.9 An owner reported an improved positive impact on quality of life after arytenoid lateralization.6 Although the vast majority of dogs improve with this surgery, complications can be seen in over half of these patients. These complications can be minor (seroma or hematoma formation) or life-threatening (aspiration pneumonia, laryngeal webbing, persistent activity intolerance). Dogs with megaesophagus have an increased risk of aspiration pneumonia, which may occur in the immediate postoperative period or years after arytenoid lateralization.7 Prognosis Dogs with neurologic comorbidities (esophageal dysfunction, hind limb weakness) had a postoperative complication rate of 71 percent compared to 30 percent in patients without these comorbities.5 Since idiopathic laryngeal paralysis is a progressive, systemic disease, it is of utmost importance to council pet owners that even with surgery, the disease will progress. Most dogs will display hind limb weakness within one year of diagnosis. Even with surgery, patients remain at risk of aspiration pneumonia for the remainder of their lives. Kendra Freeman DVM, MS, DACVS, is a graduate of Colorado State University and maintains dual certification with the American College of Veterinary Surgeons. Dr. Freeman is an associate surgeon in Albuquerque, N.Mex. Her case load consists of orthopedics, general soft tissue, and sports medicine cases with the occasional return to her roots in large animal lameness and surgery. References Tobias, Karen. Manual of small animal soft tissue surgery. John Wiley & Sons, 2017. Von Pfeil, Dirsko JF, et al. “Congenital laryngeal paralysis in Alaskan Huskies: 25 cases (2009–2014).” Journal of the American Veterinary Medical Association 253.8 (2018): 1057-1065. Letko, Anna, et al. “A CNTNAP1 missense variant is associated with canine laryngeal paralysis and polyneuropathy.” Genes 11.12 (2020): 1426. Hadji Rasouliha, Sheida, et al. “A RAPGEF6 variant constitutes a major risk factor for laryngeal paralysis in dogs. PLoS genetics 15.10 (2019): e1008416. Bookbinder, Lauren C., et al. “Idiopathic canine laryngeal paralysis as one sign of a diffuse polyneuropathy: an observational study of 90 cases (2007–2013).” Veterinary Surgery 45.2 (2016): 254-260. Sample, Susannah J., et al. “Late‐onset laryngeal paralysis: owner perception of quality of life and cause of death.” Veterinary Medicine and Science 6.3 (2020): 306-313. Stanley, Bryden J., et al. “Esophageal dysfunction in dogs with idiopathic laryngeal paralysis: a controlled cohort study.” Veterinary Surgery 39.2 (2010): 139-149. Plumb DC. Doxepin. Plumb’s Veterinary Drugs. http://app.plumbs.com/drugmonograph. Updated November 2020. Rishniw M, Sammarco J, Glass EN, Cerroni B. Effect of doxepin on quality of life in Labradors with laryngeal paralysis: A double-blinded, randomized, placebo-controlled trial. J 9. Vet Intern Med. 2021;35(4): 1943–1949. MacPhail, Catriona M., and Eric Monnet. “Outcome of and postoperative complications in dogs undergoing surgical treatment of laryngeal paralysis: 140 cases (1985–1998).” Journal of the American Veterinary Medical Association. 218.12 (2001): 1949-1956.
