Erosive rheumatoid arthritis in a young patient with mirror hand.

Mirror hand is a congenital anomaly characterised by duplication of the ulnar ray, resulting in polydactyly and functional disability of the hand. It can cause arthralgias and weakness in intrinsic muscles of the hand. We present a young woman who had a surgically corrected mirror hand and subsequently developed aggressive rheumatoid arthritis, which increased her limitations to a significant degree. Early diagnosis and treatment in such cases is very important to prevent long-term disability.