A 34-year-old woman with known rheumatic disease (psoriatic arthritis) in joints other than the temporomandibular joint (TMJ) developed condylar posterosuperior destruction and anterior disk displacement of the right symptomatic TMJ during a 7-month period, as revealed by magnetic resonance imaging. A theory is proposed that destruction of the posterior attachment by pannus was the main reason for the disk displacement, although the pannus formation itself could not be depicted. Follow-up studies also indicated the potential of magnetic resonance imaging to demonstrate fluctuation of inflammatory changes in the TMJ.