Ultrasonography (US) of distal interphalangeal (DIP) joints (a-c) and metatarsophalangeal (MTP) joints (d-f). Images on the left were acquired independently by ultrasonographer 1 (Charlotte Wiell) and middle images were acquired independently by ultrasonographer 2 (Marcin Szkudlarek) in the interobserver US substudy. (a,b) Bone proliferations (arrows) in the 2nd DIP joint on US in a palmar view in a patient with psoriasis-associated arthritis (PsA). (d,e) Synovitis (arrows) in the 2nd MTP joint on US in a dorsal view in a patient with PsA. Images on the right show a 2nd DIP joint (c) and a 2nd MTP joint (f) without destructive or inflammatory changes on US. (f) Notice subcutaneous edema dorsal to the 2nd MTP joint. DP, distal phalanx; IP, intermediate phalanx; M, metatarsal bone; PP, proximal phalanx.