Diagnostic imaging of psoriatic arthritis. Part I: etiopathogenesis, classifications and radiographic features

Abstract

Psoriatic arthritis is one of the spondyloarthritis. It is a disease of clinical heterogenicity, which may affect peripheral joints, as well as axial spine, with presence of inflammatory lesions in soft tissue, in a form of dactylitis and enthesopathy. Plain radiography remains the basic imaging modality for PsA diagnosis, although early inflammatory changes affecting soft tissue and bone marrow cannot be detected with its use, or the image is indistinctive. Typical radiographic features of PsA occur in an advanced disease, mainly within the synovial joints, but also in fibrocartilaginous joints, such as sacroiliac joints, and additionally in entheses of tendons and ligaments. Moll and Wright classified PsA into 5 subtypes: asymmetric oligoarthritis, symmetric polyarthritis, arthritis mutilans, distal interphalangeal arthritis of the hands and feet and spinal column involvement. In this part of the paper we discuss radiographic features of the disease. The next one will address magnetic resonance imaging and ultrasonography.

Keywords: diagnostic imaging; enthesitis; plain radiography; psoriatic arthritis; spondyloarthritis.

Fig. 1

Polyarticular PsA in 32 y.o. female, X-rays, A. DIP joints of the 2–4 fingers of the left hand: bony ankylosis of the DIP joint of the 4^th finger; B. the left wrist region: soft tissue swelling, radiocarpal, midcarpal and carpometacarpal joint space narrowing, osteolysis (fluffy apperacance, arrow) of the first metacarpal's base, indistinct outline of the ulnar styloid; C. right forefoot, AP at the top, oblique at the bottom: MTP 5 joint space narrowing, erosions of the medial part of the great toe's proximal phalanx and lateral aspect of the 5th metatarsal's head, osteolysis and erosion in a few interphalangeal joint with concomitant ankylosis of the DIP 2 and 3 joints, degenerative changes in the 1st MCP joint; D. AP of the pelvis: ill-defined articular surface in the anterior part of the right sacroiliac joint with marked subchondral bone osteosclerosis, within the left joint partial and simultaneous widening and narrowing of the joint space (erosions and early ankylosis), image indicative of bilateral sacroiliitis, grade 2 on the right side, grade 3 on the left side

Fig. 2

X-ray of the hands of the 53 y.o. female patient with PsA and erosive osteoarthritis, on the left – AP, on the right – PIP joint of the 5^th left finger and IP joint of the left thumb enlarged: soft tissue swelling of the ulnar side of the left wrist, malalignment of the DIP joint of the 2^nd finger of the right and 3^rd finger of the left hand, subluxation of the IP joint of the right thumb and left hand's PIP 4 joint, joint space narrowing in a few interphalangeal joints and in both wrist regions, with concomitant destructive changes and decreased distance between articular surface of the distal radius and the base of the 3rd metacarpal on the right side, gross and juxtaarticular osteoporosis, destructive changes in a few PIP and DIP joints (gull-wing appearance, erosive osteoarthritis), osteolytic and erosive lesions (fluffy appearance in the course of PsA) in PIP joint of the 5^th left finger and IP joint of the left thumb, with proximal phalangeal shortening (telescoping of finger), degenerative cyst in the head of the proximal phalanx of the 4^th left finger, erosion on the lateral side of the base of the proximal phalanx of the 2^nd right finger

Fig. 3

Foot radiograph of the 42 y.o. male patient with PsA, AP on the left, oblique on the right: osteoporosis, well-difined area of the decreased bone density in the medial part of the big toe's proximal phalanx, uneven outline of the big toe's distal bony phalanx with inflammatory cysts and medial erosion, increased bone density of the distal phalanx of the big toe (ivory phalanx)

Fig. 4

Lumbar spine AP X-ray of the 34 y.o. female patient with suspected PsA: osteoporosis, parasyndesmophytes in the thoracolumbar junction and on the left side of 4th lumbar vertebra (arrows), uneven articular surface of the sacroiliac joints as in erosions – changes indicative of bilateral sacroiliitis, grade 2

Fig. 5

AP radiograph of the sacroiliac joints: A. bilateral sacroiliitis, grade 2 on the right, grade 4 on the left, spina bifida of the last lumbar vertebra and S1; B. ill-defined articular surface of the sacroiliac joints and subchondral bone osteosclerosis, partial and simultaneous widening and narrowing of the joint space (erosions and early ankylosis), image indicative of bilateral sacroiliitis, grade 3

Fig. 6

Oblique X-ray shows a calcaneal spur (detailed evalutation on lateral radiograph), calcification adjacent to the outline of the navicular bone, degenerative changes of the forefoot