If your dog has been coughing for a while, we might be looking at a condition called chronic bronchitis.

Let’s take a look at the cough that doesn’t stop.

What is chronic bronchitis?

Bronchitis refers to inflammation (-itis) of the large airways (ie the trachea and bronchi).

Chronic refers to the length of time the condition has persisted. Chronic bronchitis may be diagnosed if your dog has been coughing on most days for more than 2 months and does not have another identifiable cause of coughing.

When the mucosal lining of the large airways is inflamed, there is increased mucus production, reduced clearance of the mucus and increased permeability of the airway barrier. This combination leads to the airways becoming thickened and more reactive to things breathed in. And this results in coughing.

Chronic bronchitis is more common in older dogs and is sometimes called old dog bronchitis. You can think of it as a bit like chronic obstructive pulmonary disease (COPD) in people.

What causes chronic bronchitis?

In most cases, we can’t identify a specific cause for the inflammation.

We do know that it’s not usually caused by infection nor is it contagious to other dogs. This is unlike acute bronchitis, which is most often due to infectious agents such as viruses (eg parainfluenza virus, adenovirus, canine influenza virus) or bacteria (eg Bordetella bronchiseptica). Infectious acute bronchitis is also called kennel cough.

Inflammation of the airways can be caused by irritants such as:

• air pollution (eg smoke)

• foreign bodies

• allergens (like hay fever in humans)

• foods allergens,

• parasites in the lungs (eg lungworm)

With most of these, we see acute bronchitis at the time of the infection or insult, which will resolve with appropriate treatment. But if bronchitis persists for more than a couple of months, it’s labelled chronic.

It’s important to know that the cough itself can begin to cause and perpetuate airway inflammation. This is why the condition is extremely hard (or impossible) to completely cure – the main symptom continues to cause the disease.

What are the signs of chronic bronchitis?

The main sign of chronic bronchitis is a persistent hacking cough, sometimes called a 'goose honking' cough. Often, the coughing occurs during the night or when the dog first starts to move around upon waking. It also commonly occurs with excitement or exercise.

Any cause of tracheal or bronchial inflammation/irritation can produce a similar-sounding cough.

How is chronic bronchitis diagnosed?

As mentioned above, a diagnosis of chronic bronchitis is made when no cause for the cough is identified. It's a 'diagnosis of exclusion'.

The conditions that we need to rule out to reach a diagnosis of chronic bronchitis include:

• tracheal collapse

• laryngeal paralysis

• lung diseases (eg pneumonia)

• lung cancer

• heart failure

• infectious causes of acute bronchitis (listed above)

Some of these can be ruled out based on history and physical examination. Others require additional testing, such as:

• chest X-rays – with chronic bronchitis, these may look reasonably normal

• bronchoscopy, which involves passing a small camera into the larynx, trachea and bronchi under general anaesthetic and collecting samples from the airways for culture and cellular analysis – with chronic bronchitis, the airways show non-specific inflammatory changes and there is little to no growth of organisms

• chest CT scan (also under general anaesthetic)

• echocardiogram (examining the heart using ultrasound)

• faecal analysis to check for parasites

It's not uncommon to have more than one condition going on at the same time. For example, we can see chronic large airway disease co-existing with other respiratory and cardiac diseases. This often becomes apparent when therapy for the 'other' disease fails to resolve the chronic coughing.

How is chronic bronchitis treated?

It's important to understand that when treating chronic bronchitis, it's very unlikely that the cough will disappear completely. The thing about coughing is that coughing induces more coughing – it irritates the airways, which stimulates more coughing.

Treatment aims to break the cycle of coughing and reduce the amount and severity of coughing by around 75%. In many cases, lifelong treatment is necessary.

Here are some of the therapies used.

Corticosteroids

Corticosteroids are useful to reduce inflammation. Often, a tapering course of orally administered corticosteroids will dramatically improve clinical signs. For patients who need long term corticosteroids, we can transition them to inhaled versions, which tends to reduce systemic side effects.

Antitussives (cough suppressants)

Antitussives can relieve clinical signs but as they don't help the underlying inflammation, we use them in conjunction with other medications (eg with corticosteroids). 

The most effective antitussives are opioids such as codeine, butorphanol and hydrocodone. Obviously, we need to weigh up the benefits and the risks of using these medications.

Bronchodilators

A medication called theophylline can be helpful for some dogs. As well as dilating (relaxing/opening up) airways, bronchodilators might have anti-inflammatory effects. Other bronchodilators, such as terbutaline or inhaled asthma treatments may also be used.

All bronchodilators have the potential to cause anxiety, characterized by pacing, panting, or restlessness.

Antibiotics

As bacteria are rarely the cause of chronic bronchitis, antibiotics are not a mainstay of therapy. That said, they are often used in patients with a recent onset of coughing to treat for possible (primary or secondary) bacterial bronchitis.

When prescribed, doxycycline is commonly chosen as it also has anti-inflammatory effects in the airways.

What else can help?

Weight loss can dramatically improve clinical signs in overweight dogs with bronchitis. Whatever other medication is given, weight loss in overweight dogs with bronchitis is very important.

Avoiding things that irritate the airways is also recommended. For example, cigarette smoke, construction dust, pollens and carpet dust can aggravate chronic bronchitis.