Systemic diseases and the pleura.

Pleural involvement in systemic diseases is usually a sign of lesions occurring at other levels. Despite the low incidence (around 1%) of pleural effusions caused by systemic diseases, more often connective tissue diseases, such as rheumatoid arthritis or systemic lupus erythematosus, may present with this. Similarly, vasculitis, such as Wegener's granulomatosis, Churg-Strauss syndrome, or less prevalent diseases, such as adult onset Still's disease, or human adjuvant disease, can also have pleural involvement. Although their incidence is low, it is important to take them into account when making a differential diagnosis of a pleural effusion. In this article, the systemic diseases that include pleural involvement are reviewed, as well as the characteristics of the effusions and their outcome.