Interstitial Pneumonia is a term used to describe a large family of non-infectious lung diseases. The most common entities include non-specific interstitial pneumonia (NSIP), hypersensitivity pneumonitis (HP), and idiopathic pulmonary fibrosis (IPF). Less common members of this family include acute interstitial pneumonia (AIP), respiratory bronchiolitis-associated interstitial pneumonia (RB-ILD), desquamative interstitial pneumonia (DIP) and lymphoid interstitial pneumonia (LIP).
The most common symptoms associated with all of these lung diseases are shortness of breath and cough. Chest imaging with high resolution CT chest is essential in further evaluating patients. The imaging pattern may be highly suggestive of a specific diagnosis or it may not provide adequate diagnostic certainty. A battery of blood tests that are commonly associated with autoimmune diseases may also be helpful. In recent years, attention has increasingly been focused on a group of patients with CT chest features of IPF but who have blood tests suggesting an autoimmune disease. The most common antibodies are anti-nuclear antibodies (ANA) and anti-synthetase antibodies. Anti-nuclear antibodies are commonly found in lupus and scleroderma . Anti-synthetase antibodies are found in dermatomyositis or polymyositis – inflammatory diseases that attack muscle and skin and often also includes severe lung involvement.
When a patient has a diagnosed autoimmune disease or connective tissue disease (CTD) and interstitial lung disease we label that as CTD-associated interstitial lung disease. However, many patients lack enough signs and symptoms of a specific connective tissue disease to make a certain diagnosis. These patients are labeled as having interstitial pneumonia with autoimmune features (IPAF). Many of these patients over time will develop a diagnosable autoimmune disease. The specific disease for which they are at risk is suggested by the pattern of antibodies present.
Treatment of interstitial pneumonia with autoimmune features is an area of active study and there is no clear consensus. In my practice, I try and determine what the pattern of antibodies suggests. I then borrow from studies of connective tissue disease associated lung disease to make treatment selections. The general approach to connective tissue disease associated lung disease is to use medicines that suppress the immune system. In scleroderma and lupus associated lung disease we have good quality data supporting mycophenolate. In contrast we have less compelling data in rheumatoid arthritis associated lung disease. In anti-synthetase syndrome (lung disease associated with polymyositis/dermatomyositis) we have moderate quality data with cyclophosphamide. We also have some data with rituximab.
A major challenge for clinicians treating interstitial pneumonia with autoimmune features is determining the role for the two new antifibrotic agents—nintedanib (OFEV) and pirfenidone (Esbriet). Recent data suggests that choosing between medications that suppress the immune system and medicines that slow fibrosis may not be essential. In a study of scleroderma patients with pulmonary fibrosis half of whom were also receiving mycophenolate, nintedanib (OFEV) was shown to be effective at slowing the rate of decline in lung function.