Reachout Orthopedics - Issue 2

been demonstrated that within 4 months of disease onset, 34.9% of patients have erosions evident on X-ray, and 54.9% were erosive at the 12th-month follow-up [15]. With the increasing use of DMARDs and biological DMARDs (bDMARDs), early diagnosis is now of paramount importance, and disease progression has to be assessed regularly to monitor efficacy of the treatment [16–18]. In addition, the identification of individual RA patients at high risk of rapid radiographic progression is critical to making appropriate treatment choices [19]. In these patients, effective therapy can reduce the odds of progression [20, 21], and both early and intensive treatment can alter the course of the disease by slowing the rate of radiographic progression [22, 23]. Regarding PsA, at the current state of the art, there is evidence supporting the concept of PsA being a distinct disease from RA clinically [24], radiologically, and patho- logically [25]. PsA develops in about 30% of patients with psoriasis [26]. It is a heteroge- neous disease, and there have been multiple attempts to subgroup patients according to their clinical presentation. As in RA, struc- tural damage is the consequence of inflam- mation that can destroy cartilage and bone, leading to functional impairment and disabil- ity [27]. In PsA, the presence of radiological damage has been enhanced in 47% of patients within the first 2 years, and as in RA, the use of bDMARDs has been capable of inhibiting progression of structural damage in several randomized controlled trials [28]. Rheumatoid Arthritis and Psoriatic Arthritis Radiographic Comparison As mentioned above, despite certain similari- ties, the two inflammatory joint diseases show considerably different features. Whereas RA primarily results in bone and cartilage resorp- tion, PsA combines destructive elements with anabolic bone responses. RA is the prototype of a destructive ar- thritis. In RA, usually, the metacarpophalan- geal (MCP) joints, the proximal interphalan- geal (PIP) joints, all wrist compartments, and the metatarsophalangeal (MTP) joints are the most commonly involved sites. In addition, joints in the midfoot and hindfoot, knees, glenohumeral joint at the shoulder, the elbow, and cervical spine can also be affected [29, 30]. In PsA, the distribution of affected joints is more often asymmetric and oligoarticular than in RA. The distal interphalangeal (DIP) joints are frequently and early involved, while in RA involvement of the DIP joints, in general, is rare and more often a feature of the late disease. In PsA, DIP joints, large joints of the lower extremities, the axial spine, and sacroiliac joints are commonly affected; the MCP and MTP joints and wrist can be involved as well. The first radiographic changes observed in RA are soft tissue swelling and juxta-artic- ular osteopenia as bone density is reduced ad- jacent to the joint as a result of local synovial inflammation [31]. The bone may appear less dense around the articular surfaces, although this is not necessarily a specific radiographic sign of RA [32]. Juxta-articular osteopenia is uncommon in PsA and, when present, is a sign of poor prognosis [33]. The lack of osteoporo- sis, even in patients with severe destructive ar- thritis, is a reliable sign in the differentiation of PsA from RA, although the presence of osteo- porosis does not exclude PsA. The erosions in RA tend to be periar- ticular and are often described as marginal erosions as they are close to the joint and reflect the direct mechanical action of the hypertrophied synovium and granulation tissue. The inflamed synovium slowly invades adjacent structures, causing damage and de- struction to the cartilage and bone, leading to joint space narrowing (JSN) and bone erosion that can be seen on radiographs. The JSN in RA tends to be uniform and concen- tric, reflecting the generalized nature of the synovial inflammation within the joint. In PsA, the early erosive changes pre- dominate in the marginal articular areas, re- sembling “mouse ears.” Erosions progress over time and may affect the central area. Later, the bone appears as if it is being gnawed away, the bone surface becomes frequently irregular or jagged but still sharply delineated, whereas peripherally new bone formation may create an unclear ill-defined outline. The ends of the bones can become pointed, resulting in the image of “pencil in cup” or “cup-and-saucer” appearance. DIP involvement and the asym- metric distribution also can help differentiate PsA from RA. The uniform reduction of joint space is the radiographic expression of car- tilage loss and could be seen at any involved joint, more typically at the DIP and PIP joints, and more infrequently at the MCP joints. The proliferation of erosions may form irregular excrescences with a spiculated ap- pearance. Along the shaft is possible to see periostitis, cottony cushion initially that may form solid new bone simulating enlargement of the phalangeal diaphysis. Periostitis in the metaphyses and diaphyses with periosteal bone neoapposition is a common phenome- non and may thicken an entire phalanx. It can occur early in the course of the disease before other features have developed. Condensation Table 1: Radiological features that distinguish between rheumatoid arthritis and psoriatic arthritis. Radiographic features Rheumatoid arthritis Psoriatic arthritis Number of erosions +++ + Severity of erosions (size) +++ ++ Erosion distribution Preponderance for radial sites Evenly distributed DIP erosions – +++ Number of osteophytes + +++ Severity of osteophytes (size) + +++ Bone proliferation + +++ Inflammatory changes  Synovitis +++ ++  Tenosynovitis +++ ++  Enthesitis + +++  Dactylitis – +++ Mutilans (erosions on both sides of joints) – + DIPs distal interphalangeal joints With the increasing use of DMARDs and biological DMARDs (bDMARDs), early diagnosis is now of paramount importance, and disease progression has to be assessed regularly to monitor efficacy of the treatment. 3 reachOut Orthopedics