Rheumatoid arthritis (RA) is an autoimmune disorder of unknown etiology characterized by symmetric, erosive synovitis and sometimes multisystem involvement. It affects 1% of the adult population and exhibits a chronic fluctuating course which may result in progressive joint destruction, deformity, disability and premature death. We review the literature data relative to the peculiar pathologic features of the disease shown by diagnostic imaging techniques.
All our patients were classified according to the diagnostic criteria of the American Rheumatism Association (1987). Plain radiography remains the diagnostic technique of choice, but ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) are also used.
Clinically articular involvement presents as pain, swelling, stiffness and motion impairment. The patients with positive rheumatoid factor are > 70% likely to develop joint damage or erosions within 2 years of disease onset. Any joint can be involved, but the proximal interphalangeal and metacarpophalangeal joints of the hand and the wrist are preferential sites, as well as the metatarsophalangeal joint of the foot, the knee and the joints of the shoulder, the ankle and the hip. Symmetry is the hallmark of joint involvement. The synovium of bursae and tendon sheaths is also affected. Soft tissue (subcutaneous nodules), muscles (weakness and atrophy) and vessels (vasculitis) may also be involved. Systemic involvement may result in Felty's syndrome, metabolic bone disorders (i.e. osteoporosis), Sjögren syndrome and pleuropulmonary abnormalities (pleural effusion, fibrosing alveolitis, constrictive bronchiolitis). The earliest abnormalities consist in synovial proliferation, soft tissue swelling, and osteoporosis. At a slightly later stage, the inflamed synovial tissue ('pannus') extends across the cartilage surface, leading to chondral erosions and small bone erosions at the joint margin (bare areas). Marginal and central erosions follow in advanced stages and finally fibrous ankylosis, joint deformities (subluxations and dislocations), fractures and fragmentations are typical findings of more advanced RA.
RA is a frequent joint disorder with a characteristic radiographic picture. Joint involvement patterns are sufficiently common to permit accurate diagnosis, especially when fusiform soft tissue swelling, regional osteoporosis, marginal and central erosions and diffuse loss of interosseous space are present. Conventional radiography remains the standard imaging technique for joint studies in the patients with suspected RA. US is recommended to diagnose soft tissue involvement (joint effusion). CT is very useful for showing abnormal processes in complex joints (sacroiliac and temporomandibular joints and craniocervical junction) which are difficult to depict completely with conventional radiography. Magnetic resonance applications include the assessment of disease activity: in particular, this technique may be the only tool differentiating synovial fluid and inflammatory pannus.