Periarticular fibrosis associated with idiopathic retroperitoneal fibrosis.

We describe a previously unreported association of retroperitoneal fibrosis with biopsy proven periarticular inflammatory fibrosis. Histologic features were strikingly similar at the 2 sites. Plasma levels of a platelet derived growth factor, connective tissue activating peptide III, were found to be elevated and may play a role in pathogenesis. A dramatic response of the periarticular process to corticosteroids correlated with improvement of other variables of disease activity.