Pulmonary Fibrosis (PF) in Dogs


Overview of Canine Pulmonary Fibrosis

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

Signs of pulmonary fibrosis in dogs may include: 

  • Tiring
  • Rapid breathing
  • Shortness of breath
  • Respiratory failure

    Coughing is remarkably absent unless there is concurrent bronchitis.


    Diagnosis of Pulmonary Fibrosis in Dogs

    Diagnostic tests are needed to recognize PF and exclude other diseases, including:

  • Complete medical history and physical examination, including careful auscultation (stethoscope examination) of the heart and lungs. Lung sounds are typically abnormal with a “crackles” noticed when the dog takes a deep breath. These abnormal sounds and shortness of breath are similar to those heard with heart failure. Tests must be completed to distinguish the conditions.
  • Radiography of the thorax (chest X-rays) is mandatory for diagnosis and to exclude other lung or chest disorders.
  • A complete blood count (CBC)
  • Testing arterial blood gas (ABG) or pulse oximetry, which is the measure of oxygen content in arterial blood, to document abnormal lung function
  • Bronchoalveolar lavage (BAL), cytology, cell differential count and culture and sensitivity are important tests in identifying inflammation of the lung and excluding some infections and cancers.
  • Lung biopsy is the only definitive diagnostic test.
  • Treatment of Pulmonary Fibrosis in Dogs

    PF is often a severe and progressive condition that causes difficulty breathing. Therapy of pulmonary fibrosis is frustrating because the underlying cause of lung inflammation or scar tissue is rarely determined or controlled. Therapy does not reverse fibrosis, though it may prevent future inflammation or lung injury. Treatments for PF may include:

  • A trial course of bronchodilators
  • Immunosuppressive doses of prednisone
  • Furosemide (Lasix®) at low doses seems to benefit some dogs though the exact reason for this is uncertain
  • Home Care and Prevention

    Weight loss in overweight dogs can reduce the work of breathing, so stick to a diet for your pet that has been prescribed by your veterinarian. Reduce your pet’s exposure to dust, chemicals and smoke.

    Exercise limitations should be imposed if your dog becomes short of breath. Provide only exercise that your pet can tolerate. Use a harness on your pet instead of a neck collar.

    Follow up with your veterinarian as needed for examination, laboratory tests and chest X-rays.

    There are not any specific recommendations for prevention of PF. Obesity should be controlled and eliminate exposure to smoke, dusts, fumes, barns and crop dust.

    In-depth Information on Pulmonary Fibrosis in Dogs

    Other medical problems can lead to symptoms similar to those encountered in pulmonary fibrosis (PF). Radiographs and bronchoalveolar lavage [BAL] will often diagnose pulmonary fibrosis.

    Further diagnostic testing may be needed to determine secondary factors such as active inflammation or to eliminate other causes of similar symptoms like heart disease. Diseases that can appear similar to those with (PF) include:

  • Bronchopneumonia or bacterial lung infection is diagnosed from radiographic appearance.
  • Chronic bronchitis or chronic inflammation of the bronchial tubes is associated with recurrent and productive coughing.
  • Congestive heart failure, which causes fluid build up in the lungs, can be a challenge to distinguish, but a cardiac evaluation should be helpful. The absence of a heart murmur in a small-breed dog virtually excludes a diagnosis of congestive heart failure from valve mitral disease, the most common reason for heart failure. An echocardiogram can rule out cardiomyopathy. It should be noted that some dogs with chronic heart failure also develop pulmonary fibrosis.
  • Heartworm disease can be diagnosed with a blood test and by X-ray inspection.
  • Inflammatory lung disease, such as pulmonary infiltrates of eosinophils (PIE), can be diagnosed with radiographs and BAL.
  • Lungworm infection requires special diagnostic fecal tests and often a sample of lung fluid for microscopic examination.
  • Pulmonary neoplasia (cancer) appears very different from fibrosis on the chest X-ray.
  • Thromboembolism, which is a clot in the blood vessels of the lung, is a real diagnostic challenge but is more likely with certain conditions.
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