Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive disease characterized by development of scarring in the lungs. The lungs become thickened and stiff, and lose their ability to support oxygen transfer into the bloodstream. In human medicine, the disease affects approximately 20 people per 100000. People over 60 are most frequently affected and mean survival time after diagnosis is between 3 and 5 years. In dogs, a similar pathology has been described and affects mainly middle-aged to older dogs of terrier breeds, and most commonly the West Highland White Terrier (WHWT). The Cairn Terrier, Scottish Terrier, Jack Russell Terrier, Bull Terrier, American Staffordshire Terrier, Yorkshire Terrier, Bichon and Shi-tzu are possibly affected as well, but are less predisposed.
To date, and despite extensive investigation, the cause of IPF remains unknown. In human medicine, fibrosis seems to be initiated by an interaction of environmental factors (such as cigarette smoking, drugs, inhalation of viral, dust or heavy metal particles) and genetic predisposition. Recently, studies in human IPF have investigated the lung microbiota. They showed associations between bacterial load, the presence of specific bacterial genera and the progression of the disease. They also suggest that the pulmonary microbiota can act as a persistent stimulus of alveolar aggression that causes fibrosis and is able to interact with the innate immune response mounted. In dogs, a genetic component is strongly suspected since the disease affects a single breed disproportionately, the West Highland White Terrier (WHWT). However, at present, preliminary genetic studies undertaken have not yet helped to identify causative mutations in this breed.
In humans, the main clinical signs include breathlessness aggravated by effort and presence of a dry cough. Generally, symptoms worsen progressively over months or years though in some people the disease remains stable for long periods or, conversely may worsen severely and rapidly. In dogs, the disease usually progresses slowly and clinical condition progressively deteriorates over months or years. The main clinical signs are exercise intolerance, cough or laborious breathing. Some dogs show episodes of syncope or cyanosis (bluish colouring of the tongue). On thoracic auscultation, diffuse harsh crackles can be heard in the majority of the cases; these are considered one of the hallmarks of the disease.
Video showing the cough that dogs may have when they are affected by pulmonary fibrosis.
Cyanosis (bluish coloration of the tongue) sometimes observed in dogs with pulmonary fibrosis secondary to a decrease in oxygen blood levels.
At thoracic auscultation, respiratory crackles are often noticed in case of pulmonary fibrosis.
In dogs, it is difficult to confirm a diagnosis of IPF. Firstly IPF needs to be distinguished from other chronic broncho-pulmonary diseases (for example, chronic bronchitis) or from disease of cardiac origin. Therefore diagnostic tests are useful, including thoracic radiography, echocardiography, bronchoscopy with analysis of the bronchoalveolar lavage fluid (under anaesthesia when judged safe enough), non-invasive pulmonary function tests such as blood gas analysis and the “6-minute-walk-test”. The most useful information can be obtained from a thoracic CT scan (High resolution tomodensitometry). However, a definitive and accurate diagnosis requires histopathological examination of a small piece of lung tissue (lung biopsy). Since this procedure requires anaesthesia, is more invasive and expensive, it is not always performed. Lung biopsies may also be collected just after the animal’s death.
6-minute-walk-test, clinical test used in order to assess the cardiopulmonary function.
Thoracic radiographies obtained from a old healthy dog (A) and a dog affected
by pulmonary fibrosis (B) showing a generalized interstitial pattern in case of disease.
Cardiac ultrasonography showing a right cardiac hypertrophy, an indirect sign of pulmonary arterial hypertension.
Endoscopy showing tracheal collapse and severe bronchomalacie, abnormalities frequently observed in case of pulmonary fibrosis.
Thoracic CT scan images obtained from an healthy dog (A) and from a dog affected by pulmonary fibrosis (B).
Healthy (A) and diseased (B) lungs observed under microscope.
The prognosis of idiopathic pulmonary fibrosis is not well established in veterinary medicine. A recent study reported a median survival of 27 months but the prognosis greatly varies from one case to another (from 2 months to more than 4 years).
While there are currently no curative effective treatments for IPF, there are a variety of therapeutic options to help patients manage their condition and maintain their quality of life and routine activities. In human medicine, Pirfenidone and Nintedanib, drugs with antifibrotic and anti-inflammatory properties, have recently been approved for use for human IPF. Unfortunately their efficacy and safety in dogs remains questionable. In humans, oxygen therapy is required in severe cases, or pending lung transplantation. In dogs, lung transplantation is not available. Similar to the situation in humans, treatment essentially aims at minimizing clinical signs and optimizing quality of life of the dog through antitussive or/and anti-inflammatory drugs. When pulmonary hypertension is present concomitantly, a treatment with type 5-phosphodiesterase inhibitors is generally beneficial. In medicine, clinical trials with various drugs are presently being investigated. We hope to be able to propose novel molecules for the treatment of our dogs with IPF in the near future.
Both in human and canine medicine, individual patient follow-up is essential. Indeed, strategies to treat IPF are highly personalized, based upon the specific patient’s medical history and other conditions (co-morbidities). A common complication in IPF dogs is the development of pulmonary arterial hypertension that leads to breathlessness and discomfort and may induce cardiac insufficiency. It is therefore advised to have your pet checked on a 4-6 monthly basis, with repetition of the non-invasive testing procedures (echocardiography and lung function tests) to permit adaptation of the treatment.