Arthritis mutilans: a report from the GRAPPA 2012 annual meeting.

Arthritis mutilans is often described as the most severe form of psoriatic arthritis. However, a widely agreed on definition of the disease has not been developed. At the 2012 annual meeting of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA), members hoped to agree on a definition of arthritis mutilans and thus facilitate clinical and molecular epidemiological research into the disease. Members discussed the clinical features of arthritis mutilans and definitions used by researchers to date; reviewed data from the ClASsification for Psoriatic ARthritis study, the Nordic psoriatic arthritis mutilans study, and the results of a premeeting survey; and participated in breakout group discussions. Through this exercise, GRAPPA members developed a broad consensus on the features of arthritis mutilans, which will help us develop a GRAPPA-endorsed definition of arthritis mutilans.