The histologic features of ILD depend on the cause of the disease, and a definitive diagnosis can only be established by pathologic examination of lung tissue. ILDs are grouped by origin, when known, and by pathologic manifestations.
Known causes include pneumoconiosis, hypersensitivity pneumonitis, certain drugs, and toxic gas inhalation. Other diseases with characteristic pathologic features include sarcoidosis, collagen vascular disease, pulmonary vasculitis, alveolar hemorrhage, bronchiolitis obliterans with organizing pneumonia, and some rare but clinically important diseases such as eosinophilic granuloma(part of the spectrum of histiocytosis X) and lymphangioleiomyomatosis.
Idiopathic pulmonary fibrosis, a disease of un known origin, can be classified into types using pathologic criteria. A few cases eluster in families, a feature that suggests a genetic predisposition. A careful and detailed history of the type and degree of environmental exposures, of the timing of symptoms relative to exposures, occupations, and drug use, and of the symptoms of collagen vascular disease is essential in patients suspected of having ILD.
Findings on physical examination depend on the degree of pathologic and physiologic abnormalities as well as on the underlying disease; typical findings include tachypnea, fine inspiratory crackles, and clubbing. Patients with sarcoidosis may have skin lesions, lacrimal and salivary gland enlargement, cranial abnormalities, or from involvement of the infiltrating granulomas.
Arthritis, alopecia, rash, or other evidence of rheumatologic disease is commonly apparent when ILD is caused by those diseases.