1 Arthritis mutilans: Arthritis mutilans is a severe, deforming, and destructive form of psoriatic arthritis that primarily affects the small joints in the fingers and toes closest to the nail.2  This leads to lost function of the involved joints. 3  It also is frequently associated with lower back and neck pain. Asymmetric psoriatic arthritis: Asymmetric arthritis typically involves one to three joints in the body -- large or small -- such as the knee, hip, or one or several fingers. 2  Asymmetric psoriatic arthritis does not affect matching pairs of joints on opposite sides of the body.