Tracheal Collapse

Tracheal collapse (ie, reduction in tracheal lumen diameter) is characterized by the flattening of the tracheal rings with laxity or redundancy of the dorsal tracheal membrane¹ and is an important differential for cough in dogs. The cause is not completely understood but is likely multifactorial, with primary and/or secondary factors (eg, reduced glycosaminoglycan/chondroitin sulfate leading to softening of cartilage) playing a role in disease progression and development of clinical signs.¹ Tracheal collapse is a progressive disease. As the tracheal cartilage weakens, the tracheal lumen patency is further compromised, and the dorsal trachealis muscle (ie, the dorsal tracheal membrane) sags into the tracheal lumen. Affected tracheal portions can include the cervical trachea, the thoracic trachea, or both. As tracheal collapse progressively worsens, the area most affected begins to collapse. Pressure changes occur during the respiratory cycle, leading to cervical trachea collapse during inspiration and thoracic trachea collapse during expiration.^1-3

Tracheal collapse is exacerbated by one or more secondary or complicating factors, including environmental allergens or triggers, obesity, lower airway collapse or disease (that includes mainstem bronchi and lower airways), respiratory infections, periodontal disease, and cardiomegaly.^1,4 Complicating factors may also include other airway abnormalities that can cause increased respiratory effort, including laryngeal paralysis or components of brachycephalic obstructive airway syndrome. Many dogs with tracheal collapse have concurrent airway collapse below the level of the trachea. As collapse and cough worsen, a cycle of inflammation and cough can occur.²

Middle-aged to older toy and small-breed dogs (eg, Yorkshire terriers, Pomeranians, pugs, poodles, Maltese, Chihuahuas) are typically affected.^1,3,5

Clinical Signs

Pet owners often describe a patient as exhibiting a progressive and worsening cough.^1,3,5 In the early stages of disease, owners typically note that the cough is intermittent and describe it as a dry, honking (or “goose-honking”) cough.⁵ However, the cough often worsens based on the presence and severity of complicating factors. As the disease progresses, the patient may experience severe coughing episodes and exhibit varying degrees of respiratory difficulty, possibly evolving into life-threatening dyspnea and cyanosis.⁵

Other signs often include a cough that is initiated or worsened by exposure to warm weather; times of excitement, exercise, or stress; and the patient pulling the leash against the trachea.¹ In addition, owners should be asked about possible environmental triggers or strong scents (eg, cigarette smoke, fragrances, floor cleaners) that may be initiating the cough.

Physical Examination

Physical examination may be relatively normal in the early stages of disease. However, as the disease progresses, tracheal palpation often elicits a cough. Many patients with collapsing trachea are overweight.^1,3 Obesity can contribute to the severity of clinical signs through a variety of mechanisms, particularly overall increased effort to breathe, which compromises respiratory capacity and function.^3,4 Obesity in dogs causes both increased resting respiratory rate and increased bronchoreactivity. Airflow appears to be limited during expiration.^6,7 Crackles or wheezes may be auscultated, particularly in patients that have concurrent small airway collapse and/or disease (eg, bronchitis),^1,3 whereas stertor and stridor may be noted in patients that have concurrent upper airway disease. If stridor is appreciated, the patient should be evaluated for laryngeal paralysis, which has been reported in dogs with tracheal collapse.^1,5 Bronchomalacia/bronchial collapse has been concurrently noted in as many as 45% to 83% of dogs with tracheal collapse.^1,2,4

A left-sided cardiac murmur may be suggestive of mitral valve disease, which is a common comorbid condition, particularly in small-breed dogs.¹ However, the role of cardiomegaly in airway collapse is unclear.¹ Patients with severe collapse may also be presented in respiratory distress and with cyanotic mucous membranes.¹

Diagnosis

Signalment, history, and physical examination findings often support a tentative diagnosis of tracheal collapse.^1-3,5 However, definitive diagnosis is made through direct visualization,⁵ ideally including collapse location and severity. Cervical or thoracic radiography, fluoroscopy, or tracheobronchoscopy can help provide visualization.^3,5,8 Although radiography and fluoroscopy can be used to evaluate tracheal collapse and mainstem bronchial collapse, they do not allow for lower airway assessment of collapse. Tracheobronchoscopy is the imaging modality of choice for evaluation of the lower airways, trachea, and mainstem bronchi.⁸

Thoracic Radiography

Thoracic radiography is warranted in all patients presented for cough. Particular attention should be placed on evaluation of the trachea and mainstem bronchi, as well as for signs of concurrent disease (eg, pulmonary, cardiac [Figure 1]). Cervical radiographs may be helpful for evaluation of the cervical trachea and thoracic inlet. However, radiographs only provide a snapshot in time; therefore, they may appear relatively normal even in a dog with significant tracheal collapse, depending on the respiratory phase captured on the images. In the author’s experience, the extent of tracheal disease is not truly represented on radiographs, and other imaging modalities may provide a more accurate clinical representation.

FIGURE 1

Lateral radiograph of a patient with severe focal collapse of the trachea in the thoracic inlet

Fluoroscopy

Fluoroscopy is a dynamic imaging modality that allows for evaluation of the trachea and mainstem bronchi, including changes in airway diameter, during all phases of respiration.³ For the clinician to best evaluate the trachea and the mainstem bronchi for collapse and severity using fluoroscopy, the patient must cough during the examination.³ This imaging modality is performed in a patient that has not been sedated or anesthetized.

Tracheobronchoscopy

Tracheobronchoscopy enables direct visualization and assessment of the lumen of the trachea, mainstem bronchi, and lower airways to assess the presence and severity of any collapse.^2,3,5 During induction of anesthesia and intubation, patients can also be assessed for laryngeal dysfunction or any components of brachycephalic obstructive airway syndrome.^1-3 Although it is considered the gold standard for assessment of the trachea and lower airways, tracheobronchoscopy requires general anesthesia, which can be risky in patients in respiratory distress.^1-3 Diagnostic samples can be collected during tracheobronchoscopy for potential infectious or inflammatory airway disease.^1-3

Differential Diagnosis

Differential diagnoses for dogs presented for cough, with or without dyspnea, include heart disease, chronic bronchitis or lower airway disease, tracheal obstruction, heartworm disease, pulmonary parenchymal disease (eg, neoplasia, pulmonary fibrosis, infectious), brachycephalic obstructive airway syndrome, laryngeal disease or paralysis, and collapsing trachea. The role of an enlarged left atrium with mitral valve disease in causing airway collapse and coughing is not completely understood.¹ In one study evaluating dogs with chronic cough and mitral valve disease, there was no difference in severity or location of airway collapse in dogs with an enlarged left atrium as compared with dogs with a normal-sized left atrium, and all dogs had cytologic evidence of airway inflammation.⁹ In another evaluating dogs with mitral valve disease, congestive heart failure was not a predictor of coughing, whereas an abnormal radiographic airway pattern and left atrial enlargement were significantly associated with coughing.¹⁰

Tracheal collapse is classified based on percent reduction in tracheal lumen size and laxity of dorsal tracheal membrane:

• Grade I: Reduced up to 25%

• Grade II: Reduced between 25% to 50%

• Grade III: Reduced between 50% to 75%

• Grade IV: Reduced between 75% to 100%; almost complete loss of tracheal lumen^1,3

Treatment & Management

Patients with tracheal collapse should ideally have an individualized treatment plan that includes appropriate identification and management of complicating factors and clinical signs associated with tracheal collapse, minimization of disease progression, and improvement in quality of life.

Immediate measures to consider in a severely dyspneic patient include supplemental oxygen therapy and sedation as indicated. The author’s preferred sedation agent is injectable butorphanol (0.2 mg/kg IV, IM, or SC as often as every 4-6 hours as needed, with care taken to avoid oversedating the patient). Other options include acepromazine, diazepam, and morphine.^1,3 Appropriate at-home management and pharmacologic measures can be started after a diagnosis has been made (see At-Home Management Recommendations).

A medical management plan should be tailored to the individual patient. If the patient is stable or exhibiting minimal clinical signs, it may be appropriate to initiate therapy with a single medication and add other drugs only when each medication alone cannot effectively control clinical signs. For more significantly affected patients, therapy with multiple medications can provide more immediate relief of clinical signs.⁴ Pharmacologic management considerations may help minimize the clinical signs associated with tracheal collapse:

• Antitussive medications (as a single medication or as a combination of medications) as needed for cough, including hydrocodone (0.25 mg/kg PO every 6-8 hours), butorphanol (0.55 mg/kg PO every 6-12 hours), diphenoxylate/atropine (0.2 mg/kg PO every 8-12 hours), and maropitant (2 mg/kg PO every 48 hours).^4,11,12 In the author’s experience, hydrocodone is most effective, and increasing the dose and frequency over time may be needed to control cough.

• Bronchodilator therapy, as indicated by the presence of lower airway disease. Bronchodilator choices include theophylline (extended release, 10 mg/kg PO every 12 hours), terbutaline (0.625-5 mg/dog PO every 12 hours), and albuterol (50 µg/kg PO every 8-12 hours).^1,4,12

• Corticosteroid therapy can help decrease airway inflammation and may include prednisone/prednisolone (starting at 1 mg/kg PO daily, tapered to the lowest effective dose). Alternatively, fluticasone (common starting dosage, 110-220 μg inhaled every 12 hours) can be administered using a face mask and spacing chamber.^1,4,11-13

• Antibiotics, ideally guided by culture of the airways, for treatment of concurrent respiratory tract infection^1,3,4

• Antianxiety or sedation medications as needed^4,5,11

In patients with an ongoing cough that cannot be controlled with medical management, evaluation for pulmonary hypertension via echocardiography should be considered.² Lower airway disease can contribute to significant pulmonary hypertension, and treatment of pulmonary hypertension with sildenafil (starting dosage, 0.5-1 mg/kg PO every 8 hours) can improve cough.² However, placement of an intraluminal tracheal stent can be considered when a patient fails to respond to aggressive and appropriate medical management and the tracheal collapse is severe enough to prevent effective ventilation.^1-4,11 During placement of a tracheal stent, fluoroscopy is used to deploy the stent across the affected portion, or entire length of the trachea, to physically hold the trachea open. This procedure is noninvasive and can be lifesaving in dogs with severe tracheal collapse (Figure 2). In dogs with tracheal collapse and concurrent complicating factors (eg, severe lower airway disease) that cannot be appropriately removed or managed, placement of a tracheal stent may not be beneficial to achieve significant improvement of clinical signs.^2,4

FIGURE 2

Stent placement across a focal severe thoracic inlet tracheal collapse

Prognosis & Complications

Patients with the best prognosis include those with minimal tracheal collapse with no complicating factors and in which therapy minimizes progression of the disease. As the disease progresses and additional management measures are needed, it can become difficult to control the disease. In dogs with severe tracheal collapse, especially when one or more complicating factors are persistently present, it can be especially difficult to control the disease. These patients have a poor prognosis for resolution of clinical signs.

Clinical Follow-Up & Monitoring

Appropriate follow-up is needed to ensure the patient is responding to the individualized medical management plan. Medications often need to be administered for 2 to 3 weeks to determine whether a positive response has been achieved. Weight loss in obese patients can be especially difficult to manage, and follow-up appointments should include assessment of weight loss. Owner observation of the patient at home is key in determining whether the current management plan is adequate, as minimizing or eliminating clinical signs is paramount for success in patients with tracheal collapse.