Interstitial lung disease (ILD) refers to a broad category of lung diseases rather than a specific disease entity and includes a variety of illnesses with diverse causes, treatments, and prognosis.

ILD with known causes are further classified based on specific exposure, association with systemic disease, or association with a known genetic disorder.

There is considerable variability among the specific diseases in presentation, tempo, and distribution of radiographic abnormalities.

For most ILDs, the plain chest radiographs will reveal reduced lung volumes with bilateral reticular or reticulonodular opacities.

A more descriptive imaging tool for ILD, high-resolution CT (HRCT), has the ability to better define the specific characteristics of lung parenchyma seen in each disease, increasing the likelihood of establishing a correct diagnosis.

A restrictive physiological impairment is the most common finding in ILDs. Both forced expiratory volume in 1 second (FEV₁) and forced vital capacity (FVC) are diminished, and the FEV₁/FVC ratio is preserved or even supranormal.

IPF is the most common ILD worldwide. HRCT typically reveals bilateral, peripheral, and basilar predominant disease with reticulonodular infiltrates, often with honeycomb, cystic change.

Asbestos-related pulmonary diseases include any diseases caused by asbestos exposure: benign asbestos pleural effusion (BAPE), rounded atelectasis, pleural plaques, mesothelioma, and certain lung cancers. The term asbestosis is not synonymous, and specifically refers to asbestos-related ILD.

Cigarette smoking is strongly associated with three types of ILD: desquamative interstitial pneumonitis (DIP), respiratory bronchiolitis-associated ILD (RB-ILD), and pulmonary Langerhans’ cell histiocytosis (PLCH).

Several drugs have been associated with pulmonary complications of various types, including interstitial inflammation and fibrosis, bronchospasm, pulmonary edema, and pleural effusions. Drugs from many different therapeutic classes can cause ILD, including chemotherapeutic agents, antibiotics, antiarrhythmic drugs, and immunosuppressive agents.

ILD is a well-known complication of several connective tissue diseases. The most commonly implicated disorders are scleroderma, rheumatoid arthritis, Sjögren’s syndrome, polymyositis/dermatomyositis, and systemic lupus erythematosus.