Pulmonary Fibrosis in Dogs

Pulmonary fibrosis is a lung disease in dogs that is characterized by chronic and progressive changes in the lung integrity. Lungs become scarred, stiff, and thickened which results in respiratory distress and impaired oxygenation. Classic pulmonary fibrosis is thought to be an inflammatory disease that results from chronic injury and healing of the lung tissue. Conditions such as pneumonia, chronic bronchitis, congestive heart failure, and environmental pollutants damage the pleural tissue. Although the conditions themselves may improve with treatment, damage to the lung tissue is irreversible. In idiopathic pulmonary fibrosis, the cause remains unknown. This condition is not triggered by an inflammatory process, but does seem to have a genetic link. Terriers, especially the West Highland White Terrier, are at risk for developing this disorder. 

Dogs present with symptoms of exercise intolerance, respiratory distress, decreased appetite, and cough. Unlike pneumonia, viral illnesses, or congestive heart failure, the symptoms do not improve with conventional treatment. Extremely loud “crackles” are frequently heard in the lungs during a routine veterinary visit. The vet may order additional diagnostic testing to confirm the diagnosis of pulmonary fibrosis. CT scan, x-rays, blood work, bronchoscopy, and ultrasound provide valuable information in diagnosing this condition.

Pulmonary fibrosis is a chronic, progressive, and incurable condition. Veterinary management is aimed at reducing the symptoms associated with the disorder. Medications including steroids, bronchodilators, sedatives, and cough suppressants may provide some relief, but do not seem to decrease the progression of the disorder. The average life expectancy of a dog diagnosed with pulmonary fibrosis is 12-18 months, but may vary based on the degree of lung damage at point of diagnosis.

Pulmonary fibrosis is a chronic and progressive disease that causes scarring in the lungs. Because the lungs become stiff and thickened, it is difficult to maintain adequate oxygenation of the body.

• Exercise intolerance
• Rapid respiratory rate
• Wheezing
• Cough
• Cyanosis (blue color of the tongue)
• Open mouthed breathing
• Lethargy
• Decreased appetite
• Syncope (dizziness and fainting)

Types

• Pulmonary interstitial fibrosis is thought to be an inflammatory process caused by chronic injury and repair to the lung tissue
• Idiopathic pulmonary fibrosis is a noninflammatory and progressive fibrotic lung disease with no identifiable cause

Pulmonary interstitial fibrosis is thought to be caused by chronic injury and repair to the interstitial tissue of the lung. Injury and inflammation can result from:

• Chronic Bronchitis
• Viral illness
• Chronic dirofilaria and leishmania infections
• Congestive heart failure
• Pneumonia
• Environmental exposure to chemicals, polluted air, or cigarette smoke
• Tumors
• Acute pancreatitis

With idiopathic pulmonary fibrosis the cause of the disease is unknown, there appears to be a strong genetic component. 

• West Highland White Terriers are the breed most affected by pulmonary fibrosis;  other terrier breeds such as the Jack Russell terrier and the Staffordshire terriers are at increased risk for developing the disorder and Poodles are at a slightly higher risk of the condition 
• Increased age seems to contribute to the onset of the disorder with typical age of onset 9 years

Dogs present to the veterinary office with symptoms of respiratory distress, exercise intolerance, and cough. These symptoms can be indicative of other more common conditions such as pneumonia or congestive heart failure. Upon auscultation with a stethoscope, extremely loud “crackles” are often heard suggesting impaired air movement in the lung. Your dog may have an elevated respiratory rate and increased respiratory effort. In some dogs, there may also be a heart murmur. If the doctor suspects pulmonary fibrosis, there are several tests and procedures including:

• Chest x-ray – Will often show a heavy interstitial pattern without signs of infection or enlarged heart
• Blood tests may rule out infectious causes
• Bronchoscopy may be used to rule out chronic bronchitis and collect cells for cytologic examination
• Ultrasound can provide further information about degree of fibrosis and arterial function in the lungs
• CT scans of the chest are now being used to provide detailed information about the degree of fibrosis

Pulmonary fibrosis is a chronic and progressive condition for which there is no cure. Lung damage is irreversible. Therapeutic goals include controlling complications and clinical symptoms of the disease. Treatment options include:

• Corticosteroids, but there is no proof that steroids will slow the progression of the disease
• Oxygen supplementation may be used for severe respiratory distress in inpatient settings, but is not practical for outpatient use
• Bronchodilators such as theophylline may be used to increase aeration in the lungs
• Cough suppressants such as hydrocodone or butorphanol may improve quality of life
• Dogs should be allowed to self-limit activity 
• Sedatives such as acepromazine may be used to decrease anxiety associated with severe respiratory distress 
• Viagra (sildenafil) may be used to treat pulmonary hypertension that develops in the late stages of the condition