Pulmonary fibrosis (PF) is the presence of increased fibrous (scar) tissue in the lungs as a consequence of lung tissue injury. The exact cause in most cases is unknown; however, underlying progressive inflammation of the alveoli (alveolitis), injury or recurrent congestion of the lung (as with heart failure) seem to predispose dogs to PF.

Hundreds of inhaled, ingested and administered chemicals, dusts, gases, pollutants and drugs are capable of inducing lung fibrosis in humans. Presumably, dogs react in a similar manner. Inorganic and organic dusts, gases and vapors, drugs and infectious agents have been implicated, but pinpointing an exact cause is difficult.

Fibrosis of the lungs makes the lungs stiffer and prevents normal expansion. There is usually impaired movement of oxygen across the lungs and low oxygen content in the blood. These problems lead to tiring and shortness of breath.

It is quite likely that severe, diffuse lung fibrosis in middle-aged and older dogs is preceded by alveolitis similar to that associated with chronic pulmonary fibrosis in humans.

The typical dog with pulmonary fibrosis is an older small or medium sized breed. Many dogs are concurrently overweight. Some are also be affected by bronchitis (inflammation of the bronchial tree, similar to a smoker's cough). Small terrier breeds, especially West Highland white terriers are predisposed to this problem.

What to Watch For

Tiring

Rapid breathing

Shortness of breath

Respiratory failure

Coughing is remarkably absent unless there is concurrent bronchitis.