An idiopathic interstitial pneumonia characterized by lung inflammation and scarring that obstructs the small airways and air sacs of the lungs (alveoli). A flu-like illness, with a cough, fever, a feeling of illness (malaise), fatigue, and weight loss, heralds the onset in about 50% of people. Frequent presence of crackling sounds (called Velcro crackles) when the doctor listens with a stethoscope.