Canine Laryngeal Paralysis

Introduction

Laryngeal paralysis is a relatively common condition particularly in older large breed dogs. Although diagnosis and treatment appear straight forward, there are many questions about laryngeal paralysis that remain unanswered. Controversy also exists regarding the longterm outcome following surgery. A recent large retrospective study performed at Colorado State University (CSU) found a higher postoperative complication rate than previously reported and it identified several risk factors that may increase surgical morbidity. This is in contrast to studies that describe good to excellent outcomes in 80 to 90% of dogs. Based on this discrepancy, we are continually examining the issues that surround the diagnosis and management of this disease.

Work-Up

The routine work-up for a dog suspected to have bilateral laryngeal paralysis includes physical exam, neurologic exam, CBC, biochemical profile, urinalysis, thoracic radiographs, thyroid function screening, laryngeal examination, ± esophagram, and ± cervical radiographs. Dogs should be thoroughly evaluated for possible underlying etiologies of laryngeal paralysis. Definitive diagnosis of laryngeal paralysis requires visual examination of larynx. Suspicion of this condition arises from the history of the dog as well as consistent clinical signs. Typically, a light plane of anesthesia is induced using intravenous thiopental, propofol, or ketamine / diazepam combination. However, laryngeal examination is a poorly specific diagnostic test as false positives are common due to the influence of anesthetic agents on laryngeal function. Diagnosis may also be confused by the presence of paradoxical movement of the arytenoids resulting in a false negative result. In this situation the arytenoid cartilages move inward during inspiration due to negative pressure created in the trachea by breathing against a severe obstruction. The cartilages then return to their original position during the expiratory phase giving the impression of abduction. An assistant can state the stage of respiration during the examination to help distinguish normal from abnormal motion. Doxapram HCL (1mg/kg, IV) has been advocated for routine use during laryngeal examination to increase respiratory effort and intrinsic laryngeal motion.

Surgical Candidates

Dogs are often not severely clinical until they have bilateral laryngeal paresis or paralysis. Therefore, dogs with unilateral laryngeal dysfunction are not usually surgical candidates. For dogs with bilateral laryngeal paralysis, the decision to go to surgery is based on the quality of life of the dog, severity of clinical signs, and the time of the year. Warmer weather causes dogs to breathe harder with less physical exertion. Increased respiratory rate and effort against a fixed upper airway obstruction results in laryngeal cartilage swelling. This creates a vicious circle as the swelling increases the degree of obstruction, which increases the effort of respiration, which increases laryngeal swelling, and so forth. [...]