“Why does my dog cough like that?”
By Dr. Gail Mason, DVM, MA, DACVIM
Staff Internist, Portland Veterinary Emergency & Specialty Care
The trachea, also known as the windpipe, is the structural conduit from the oral cavity to the lungs. Tracheal “collapse” is a chronic, progressive, and irreversible disease of the trachea and the larger bronchial tubes. This disorder likely has a genetic component and is most commonly seen in small breeds such as the chihuahua, poodle, Yorkshire terrier, and Pomeranian. Structurally, the normal trachea is fairly rigid, with C-shaped rings much like a vacuum cleaner hose. The opening of the “C” faces towards the dog’s back. The gap in the “C” is covered by a muscle known as the tracheal membrane.
Tracheal collapse results from a weakening of the cartilage rings (referred to as tracheomalacia) that start to collapse and there is a loss of the normal curvature. As a result, the tracheal membrane becomes stretched and floppy, which can result in airway obstruction. The sensation of the flaccid tracheal membrane touching the inner lining of the trachea initiates coughing spasms. Adding to this problem, inflammation occurs within the trachea which results in increased mucus secretion, and the release of enzymes that further soften the tracheal cartilage. The trachea can collapse along its entire length, only within the chest cavity (“intrathoracic”) section, or only the segment outside the chest cavity (“extrathoracic”) in the neck region. The most affected segment is that which is where the trachea enters the chest cavity.
Severely affected animals can demonstrate symptoms at an early age. However, many dogs with collapsed trachea do not show symptoms until other health problems develop. Common concurrent diseases include obesity, hypothyroidism (low levels of thyroid hormones), respiratory infections or irritants, heart enlargement, or excess production of cortisone in the body secondary to hyperadrenocorticism or “Cushing’s disease.”
How is tracheal collapse diagnosed?
Any dog suspected of having tracheal collapse should be evaluated by a veterinary professional. A medical history including signs and symptoms, routine blood work, and a physical examination can raise the index of suspicion for a diagnosis of tracheal collapse. Radiographs or “chest X-rays" may be helpful in the diagnosis. Though tracheal collapse is not always visible on routine X-rays, the heart and lungs can also be evaluated. Fluoroscopy is a technique in which the animal's chest and trachea are viewed using a “moving X-ray” technique. The patient is awake, which allows a dynamic view of the breathing process. Bronchoscopy is a fiberoptic scope method to visually inspect the oral cavity, trachea, and the larger airways. Though it does require anesthesia to perform, samples can be obtained for analysis and bacterial culture which may aid in the diagnosis of contributing factors.
What can be done for dogs with tracheal collapse?
In a recent retrospective study of a hundred dogs with collapsing trachea, 71% of patients responded well to medication and management of secondary factors such as obesity, infection, or airway irritants. Another 6% had severe enough collapse that they succumbed to their disease. Approximately 16% of patients who failed medical management became eligible for surgical intervention.
Medical management may include a patient weight-loss program, the elimination of airway irritants such as fireplace or cigarette smoke, and treatment for secondary infection. Treatment for existing illnesses such as Cushing’s disease, hypothyroidism, or diabetes mellitus can improve patient outcomes. Cough suppressants such as hydrocodone, butorphanol, or tramadol can be useful in breaking the cycle of coughing. Steroids including prednisone can be useful in reducing mucus production and inflammation within the airway. They must be used judiciously as high-dose steroids can further weaken the tracheal cartilage.
A bronchodilator such as theophylline or terbutaline can be useful to dilate the lower airways, relieving pressure within the chest during inhalation. While they don't have a direct effect on the trachea itself, the reduction of negative pressure can reduce the degree of tracheal collapse.
What if these options don’t work?
If patients can have their tracheal collapse managed medically, it is the preferred treatment. However, in severely affected patients, it is possible that surgical intervention would be of benefit. Surgical management includes two options. The first is called a "ring prosthesis." This is a procedure where a rigid prosthetic is placed and bonded around the trachea, essentially creating a non-collapsible tube. The procedure requires that the collapsed region of the trachea is external to the chest cavity. The second method is the use of a “tracheal stent.” This is a cylindrical, stainless steel, self-expanding tube that is placed inside the collapsed portion of the dog's trachea. Overall, the success rate reported is 75-90% where 30% were recorded to be free of symptoms and 61% showed marked improvement. It is important to remember that these procedures carry certain risks and should be performed by a board-certified veterinary specialist.
Is this an emergency?
Dogs that are severely affected by this disorder can suffer respiratory distress, which can be life-threatening. Those that exhibit prolonged coughing episodes, have a blue tinge to their gums and tongue, and have increased respiratory efforts should be seen on an emergent basis. If you happen to have a pet with this disorder, knowledge is power! With careful attention and oversight by your dog’s veterinarian, most patients can enjoy a full life.