Psoriatic Arthritis

The association of psoriasis with a specific type of arthritis is well established. Psoriatic arthritis may co-occur with, but is not related to, rheumatoid arthritis, and can be differentiated on the basis of asymmetrical spotty distribution, positive HLA-B27 antigen test, negative rheumatoid factor, and the radiographic and scintigraphic findings. Occasionally, however,

Asymmetrical Psoriatic ArthritisAsymmetrical Psoriatic Arthritis

a symmetrical polyarthritic form may be encountered, strongly mimicking rheumatoid arthritis (Fig. 11.23). Psoriatic arthritis is relatively uncommon with a prevalence of probably no more than 5% (Hellgren 1969). The positiv-ity for HLA-B27 antigen in psoriasis ranges from 46% to 78%, which is relatively low compared to Reiter's syndrome and ankylosing spondyloarthropathy.

The clinical onset is insidious in most cases, but in about one-third it may present with acute manifestation. Psoriatic arthritis affects both sexes nearly equally, with the peak incidence occurring between the mid-30s and mid-40s of life. The strong proclivity for the involvement of the distal interphalangeal joints of the hands and feet is an important, but not a sine qua non, finding (Resnick and Niwayama 1988). The interphalangeal joints, metacarpo-phalangeal joints, and metatarsophalangeal joints are most commonly affected. The ankles, knees, wrists, and spine are not exempt, but significant change is unusual in the shoulders and hips. The distribution is characteristically asymmetrical and oligoarticular as in Reiter's syndrome, but symmetrical and polyarticular involvement may also occur (Fig. 11.23).

The fundamental pathology in peripheral psoriatic arthritis is synovitis, which is characterized by villous hypertrophy, lymphocytic infiltration, proliferating fibroblasts, and vascular necrosis. In the late stage the distal inter-phalangeal joints may become destroyed, subluxed, and disfigured with marginal bony

Fig. 11.24A, B Typical distal interphalangeal joint involvement in psoriatic arthritis. A Dorsoventral radiograph of the right hand in a 64-year-old male with longstanding psoriasis shows marked narrowing and eburnation of the distal and proximal interphalangeal joints as well as the metacarpophalangeal joint. The second finger is foreshortened due to flexure contracture and telescoping of the metacarpophalangeal joint (curved arrow). The third metacarpophalangeal joint shows the "knuckle" sign (arrows). B Dorsal pinhole scintigraph reveals intense tracer uptake in the distal interphalangeal joints (arrowheads) and foreshortening of the second finger (curved arrow) and the "knuckle" sign of the third finger (arrow)

Psoriatic Arthritis The Ankle

Fig. 11.25A, B Psoriatic arthritis in the foot. A Dorso-plantar radiograph of the left foot in a 37-year-old male with psoriasis shows narrowing and blurring of the first through third metatarsophalangeal joints as well as the first interphalangeal joint (arrows). B Dorsal pinhole scintigraph reveals intense tracer uptake in the affected joints with the "knuckle" sign in the great toe (twin arrows)

Fig. 11.25A, B Psoriatic arthritis in the foot. A Dorso-plantar radiograph of the left foot in a 37-year-old male with psoriasis shows narrowing and blurring of the first through third metatarsophalangeal joints as well as the first interphalangeal joint (arrows). B Dorsal pinhole scintigraph reveals intense tracer uptake in the affected joints with the "knuckle" sign in the great toe (twin arrows)

excrescences due to enthesopathy. Lesions are asymmetrical and sparse and even unilateral in occasional cases, more regularly affecting the upper extremity including the fingers. In about 5% of cases the distal phalanx melts away completely, resulting in arthritis mutilans.

Radiographic manifestations are periarticu-lar swelling, articular narrowing, subchondral bone erosions, and bony excrescence, and "whiskering". Both the distal and proximal interphalangeal joints are more regularly i nvolved than other joints in the hands and

Proximal Interphalangeal Joint Toe

Fig. 11.26A, B Achilles tendoenthesitis in psoriasis. A Lateral radiograph of the right hindfoot in a 64-year-old male with psoriasis shows very subtle thickening of the distal Achilles tendon (right upper arrow) with a fractured new bone formed at the calcaneal insertion (right lower arrow). The talocrural, talonavicular, and subtalar joints are all diffusely narrowed (single arrow). B Lateral pinhole scintigraph reveals tracer uptake in the distal Achilles tendon and fractured new bone (arrows) as well as peritalar joints. Note especially intense uptake in newly formed bone that is fractured

Fig. 11.26A, B Achilles tendoenthesitis in psoriasis. A Lateral radiograph of the right hindfoot in a 64-year-old male with psoriasis shows very subtle thickening of the distal Achilles tendon (right upper arrow) with a fractured new bone formed at the calcaneal insertion (right lower arrow). The talocrural, talonavicular, and subtalar joints are all diffusely narrowed (single arrow). B Lateral pinhole scintigraph reveals tracer uptake in the distal Achilles tendon and fractured new bone (arrows) as well as peritalar joints. Note especially intense uptake in newly formed bone that is fractured feet (Figs. 11.23 and 11.24A). Resorption or lysis of the tufts, the "pencil and cup" appearance of the digits, subluxation, ankylosis, and telescoping may occur in severe cases. The individual articular changes are often indistinguishable from those of rheumatoid arthritis, but bony excrescences and mild or absent osteopenia deserve recognition as differential points.

Pinhole scintigraphic manifestations of the large and small joints of the limbs are essentially the same as in Reiter's syndrome and ankylosing spondylitis when disease is protracted. Articular psoriasis is indicated by marked tracer uptake, typically in the distal interphalan-geal joints of the hands and feet (Fig. 11.23). Dwarfing and subluxation of fingers may occur in advanced cases (Fig. 11.24B). The scintigraphic features of toe involvement are not dissimilar to those of Reiter's syndrome (Fig. 11.25). In occasional cases pinhole scintigraphy can detect tendinitis or enthesitis by showing subtle tracer uptake, which is difficult to appreciate on ordinary planar scintigraphs (Fig. 11. 26).

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