A case of isolated IgG4-related interstitial pneumonia: a new consideration for the cause of idiopathic nonspecific interstitial pneumonia.

The 2008 American Thoracic Society Project concluded that idiopathic nonspecific interstitial pneumonia (NSIP), once regarded as a "provisional" diagnosis, can be considered a distinct clinical entity. However, an increasing number of recent reports have shown a likely link between the entity of idiopathic NSIP and autoimmune diseases. Similarly, IgG4-related disease is being increasingly reported, and some of the lung lesions, at least radiologically, look like NSIP. A case of IgG4-related interstitial lung disease without other systemic manifestations of IgG4-related disease is reported. The existence of IgG4-related disease should, therefore, be taken into consideration as a possible differential diagnosis from NSIP. The cause of IgG4-related disease remains unknown, but we emphasize the importance of a clinically novel interstitial lung disease.