Chapter 21: Table of Contents
Tracheal collapse (also known as tracheochondromalacia) is a progressive degenerative condition of the c-shaped tracheal cartilages that leads to softening of the cartilages and dorso-ventral collapse with or without laxity of the dorsal tracheal membrane. Tracheal collapse is classified as a dynamic airway condition because the collapse varies with airway pressure changes. It is typically associated with an intermittent ‘honking’ cough but can also lead to severe respiratory distress that requires emergency therapy. Middle aged, toy and miniature breed dogs such as Yorkshire Terriers, miniature and toy poodles, Pomeranians, Chihuahua, Maltese and Pugs are most commonly affected but a genetic cause has not yet been identified.
Initial diagnosis is typically based on signalment and history along with evidence of respiratory difficulty and typically a honking cough. Clinical signs include wheezing, dyspnea, coughing (‘goose honk’ or otherwise), exercise intolerance, cyanosis and syncope. Palpation of the cervical region may reveal a palpably soft trachea and might induce a coughing episode. Observation of the patient (phase of breathing) can help determine whether the collapse involves the cervical, thoracic or both sections of the trachea. It is important to note that a small percentage of patients have concurrent laryngeal paralysis which can lead to inspiratory stridor and compound the upper airway obstruction. Very proximal tracheal collapse can also present like laryngeal paralysis with more of a roaring sound than a honking cough. Careful thoracic auscultation should be performed to rule-out cardiac or lung involvement.
History taking is extremely important and should include information such as age at onset and progression of signs over time, frequency and severity of signs (including whether any episodes of collapse or severe dyspnea have ever occurred) and whether there are any inciting causes or situations (exercise, stress, visitors, etc.) that worsen the clinical signs. One should also inquire about previous medical management and response to treatment as well as environmental factors such as exposure to scented products, dust, cigarette smoke, etc. Confirmation of the diagnosis typically involves radiography (inspiratory and expiratory +/- positive and negative airway pressure), fluoroscopy, and tracheo-bronchoscopy. Although lateral thoracic radiographs performed at rest are diagnostic approximately 60% of patients, fluoroscopic examination (standing or in lateral recumbency) during a coughing episode is more likely to document the presence and severity of a dynamic tracheal collapse. Note that inspiratory and expiratory radiographs are best since the cervical trachea tends to collapse during inspiration and the thoracic trachea tends to collapse during expiration. Tracheo-bronchoscopy has been described as the gold standard for diagnosing tracheal collapse. It allows grading of the collapse and is the best method to assess mainstem bronchi collapse. In addition, during tracheoscopy, samples can be collected for cytology and bacterial culture. Tracheal collapse is generally graded based on the degree of collapse of the rings and laxity of the dorsal membrane with Grade 1: 25% decrease in luminal diameter, Grade 2: 50% decrease in luminal diameter, Grade 3: 75% decrease in luminal diameter and Grade 4: 100% decrease in luminal diameter. Though rarely an issue, laryngeal examination should be performed before intubation to assess laryngeal function as this will affect treatment and prognosis