Giant cell arteritis precipitated by a diagnostic trial of prednisolone in suspected polymyalgia rheumatica.

A 62-year-old woman developed symptoms of polymyalgia rheumatica (PMR), but without clinical evidence of concomitant giant cell arteritis (GCA). A single blind, placebo-controlled trial of prednisolone confirmed the diagnosis, but in addition unwittingly exposed clinically silent giant cell arteritis.