A rare syndrome of unknown etiology characterized by progressive fibrosis involving multiple organ sites.

Multifocal fibrosclerosis and idiopathic fibrosclerosis are disorders of unknown aetiology, characterised by fibrous lesions (co-)occurring at a variety of sites. Known manifestations include retroperitoneal fibrosis, mediastinal fibrosis and Riedel's thyroiditis. They are now considered to be manifestations of IgG4-related disease..