Tracheal collapse

What it is

Tracheal collapse is a degenerative disease of the tracheal cartilage, which loses glycosaminoglycans, chondroitin and water and becomes soft. The C-shaped rings flatten and the dorsal tracheal membrane (trachealis muscle and its covering) becomes lax and protrudes into the lumen. Collapse is dynamic: the cervical trachea tends to collapse during inspiration and the intrathoracic trachea during expiration and coughing. It often coexists with bronchomalacia, chronic bronchitis, obesity and heart disease, which worsen the cough.

Who it affects

Toy and small breeds, usually middle-aged: Yorkshire terrier, Pomeranian, Chihuahua, toy poodle, Maltese, pug. Signs may start earlier in severe cases.

Anatomy involved

• Trachea: cervical, thoracic inlet and intrathoracic segments, alone or together; the carina and principal bronchi may also collapse.
• Dorsal tracheal membrane: the redundant membrane is what narrows the lumen in most dogs.
• The disease is graded I to IV according to the loss of lumen (from about 25% to complete collapse with the membrane touching the cartilage).

Clinical signs

A dry, harsh, paroxysmal cough that sounds like a goose honk, triggered by excitement, drinking, eating, pulling on a collar or tracheal palpation. Exercise intolerance, inspiratory or expiratory stridor, and in severe cases respiratory distress, cyanosis and syncope. Heat, stress and obesity aggravate it.

Diagnosis

• Physical examination: gentle tracheal palpation readily elicits the cough.
• Inspiratory and expiratory cervical and thoracic radiographs: may show narrowing, but are insensitive because collapse is dynamic; overlapping oesophagus or the longus colli muscles can mimic it.
• Fluoroscopy: shows the dynamic collapse during breathing and coughing.
• Tracheobronchoscopy: confirms and grades the collapse, assesses the bronchi and allows airway lavage to look for infection or inflammation.

Treatment

Most dogs are managed medically: weight loss, a harness instead of a collar, avoiding heat and smoke, antitussives (for example butorphanol or hydrocodone), short courses of corticosteroids for airway inflammation, and treating concurrent disease. Dogs with severe collapse that does not respond can be treated with extraluminal prosthetic rings (cervical collapse) or an intraluminal self-expanding stent; both have specific complications and are done in specialist centres.