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.

In-depth Information on Diagnosis

Diagnostic tests are needed to recognize PF in dogs. A tentative diagnosis can often be made based on the results of the history, physical examination and chest X-rays. In diagnosing PF, it is important to exclude other diseases and your veterinarian may refer you to a specialist if the diagnosis is in doubt. Details about the different diagnostic tests include:

• Complete medical history and physical examination
• Radiography (chest X-rays) to detect a mild diffuse increase in interstitial lung densities, which is generally evident throughout the lungs in dogs with PF. Bronchial markings may be prominent, especially if there is also bronchitis.
• A complete blood count (CBC) to determine general health and check for secondary conditions. The CBC in dogs with PF is usually normal.
• Biochemistry and serum blood tests to determine general health and check for secondary conditions.
• A heartworm test
• Testing arterial blood gases to determine oxygen levels. This is a sensitive test for verifying the presence of significant lung disease. Many veterinary hospitals do not have the equipment to run this test but blood can be analyzed easily at a local human hospital.
• A pulse oximetry test to measures oxygen content of arterial blood. This test provides information similar to an arterial blood gas but is not as sensitive as the blood gas. However, if the pulse oximetry shows abnormal oxygen content, this is sufficient.
• A tracheal wash, also called a transtracheal wash, in which a fluid sample from the trachea (windpipe) is obtained and analyzed. This test is done under local anesthetic by inserting a needle and catheter across the trachea and advancing the catheter into the windpipe. This test is most advantageous in coughing dogs.
• Bronchoalveolar lavage (BAL) is a test in which fluid samples from the bronchus and alveolar (lung) tissues are obtained. There are a number of techniques used, and anesthesia is required. This test results are abnormal in active alveolitis/fibrosis (lung inflammation leading to scar tissue). The sample results are characterized by increased neutrophils but without evidence of an infection.
• Bronchoscopy, which is a procedure consisting of placing a small flexible fiberoptic tube into the airway. It can be used to visualize the airways and perform a BAL test, and will usually establish the diagnosis and rule out other potential lung diseases, such as inflammatory lung disease, lungworms, fungal infections and cancer. This is often a referral procedure.
• A fine-needle lung aspirate, which is a procedure that consists of placing a small needle into the lungs and obtaining a small tissue sample. It is one method of identifying diffuse lung disease caused by cancer or certain infections.
• Lung biopsy, the surgical removal of a piece of lung tissue, can lead to a definitive diagnosis of lung fibrosis. However, it is an invasive test and is rarely done.

In-depth Information on Treatment

Treatments for PF in dogs may include one or more of the following:

• Treatment of PF must be individualized based on the severity of the condition, the cause, secondary diseases or conditions and other factors that must be analyzed by your veterinarian. Therapy of idiopathic pulmonary fibrosis is frustrating because as the underlying cause of lung inflammation is rarely determined or controlled and therapy does not reverse pre-existent fibrosis.
• A trial course of bronchodilators using sustained-release theophylline, aminophylline or oxtriphylline should be considered.
• Bronchodilator drugs may increase the vigor of contraction of the respiratory muscles, which may be useful in dogs with chronic shortness of breath.
• Antibiotics are not helpful.
• Prednisone can be used if tests (BAL) determine active airway inflammation with an absence of infection. This will not reverse the existing fibrosis but may decrease ongoing lung inflammation (alveolitis) and prevent further damage. Chronic treatment is controversial but one approach is to prescribe pulsed prednisone (for example, twice-daily dosing for one week per month).
• The benefits, if any, of the immunosuppressive drug, cyclophosphamide, have not been evaluated in the dog but this is commonly used in humans with PF and active alveolitis.
• The prognosis in advanced pulmonary fibrosis is unfavorable and gradual clinical deterioration is expected. Severe hypoxemia (low oxygen content in blood) or progressive right-sided heart dysfunction may be observed in very advanced cases.
• Many dogs are eventually euthanized.

Follow-up Care for Dogs with Pulmonary Fibrosis

Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow-up can be critical and may include the following:

• Administer prescribed medications as directed by your veterinarian. Be certain to contact your veterinarian if you are experiencing problems treating your dog.
• Serial blood gas determinations and bronchoalveolar lavage cytology may be done to monitor therapy and the clinical course of the disease, though this is infrequently done because of the need for general anesthesia.
• Eliminate smoke, chemicals, dusts or fumes from your pet’s environment.
• Notify your veterinarian if your dog is coughing. This is a prominent clinical sign and bronchitis is likely to be present. This is a different diagnosis than PF.
• Control your dog’s obesity. Discuss a weight loss plan if your dog is obese.