An organised approach to Interstitial lung diseases:
Systemic Diseases: the most common of these are sarcoidosis and the Collagen Vascular Diseases - with scleroderma being the prototype. Also consider mixed connective tissue diseases. ILD is not as commonly in SLE and Rheumatoid arthritis.
Here is a good review article on sarcoidosis.
Exposures: these are classically divided up into organic and inorganic.
- Organic: aka hypersensitivity pneumonitis. Think about Bird Fancier's Lung (proteins in bird excrement), Cheese Washers Lung, Farmer's Lung, and many many more.
- Inorganic: aka pneumoconiosis. This would include exposure to dust from asbestos, silica, and coal.
Drugs: Exposure to alkylating chemotherapeutic agents (eg bleomycin), and commonly used meds like amiodarone, methotrexate, nitrofurantoin, and sulfa drugs.
Idiopathic: This is a strange category with bizarre acronyms. It doesn't help that there are new and old acronyms for some of the pathologies, but all are still commonly used. Here's a sample.
- Usual Interstitial Pneumonia (UIP), also known as Interstitial Pulmonary Fibrosis (IPF). This is the most common of the idiopathic interstitial lung diseases. Here is a good review article.
- Acute Interstitial Pneumonia (AIP) also known as the Hamman-Rich Syndrome. Just like UIP, but more rapid and severe.
- Cryptogenic Organising Pneumonia (COP), but if the etiology is known, it will be called Bronchiolitis Obliterans with Organizing Pneumonia (BOOP). Lots of granulation tissue in the small airways here.
- Desquamative Interstitial Pneumonia (DIP). Many macrophages in alveoli. Common in middle-aged smokers. A milder version of this may be referred to as Respiratory Bronchilitis-Associated Interstitial Lung Disease (RBILD).
- Others: Lymphocytic Interstitail Pneumonia (LIP), Nonspecific Interstitial Pneumonia (NSIP).
Other Rare Causes: Alveolar hemmorhage, Pulmonary Infiltrates with Eosinophilia (PIE), Pulmonary Alveolar Proteinosis (PAP), Lymphangioleiomyomatosis (LAM).
Mimickers of ILD: Congestive heart failure, certain infections like Pneumocystis Carini Pneumonia, and lymphangitic carcinomatosis can cause interstitial pattersns on chest X-rays.