Juvenile idiopathic arthritis (JIA) is a heterogeneous group of disorders of unknown cause that present with arthritis before age 16 and persist for at least 6 weeks. In contrast to RA, in JIA: (1) oligoarthritis is more common, systemic disease is more frequent, (3) large joints are affected more often than small joints, (4) rheumatoid nodules and rheumatoid factor are usually absent, and anti-nuclear antibody (ANA) seropositivity is common. The pathogenesis is unknown but similar to adult RA; risk factors include HLA and PTPN22 variants. Also, like adult RA, damage in JIA appears to be caused by TH1 and TH17 cells and cytokines produced by these and other inflammatory cells. Treatment is similar to adult RA with some success in using an IL-6 receptor antibody in the systemic form. Long-term prognosis of JIA is very variable. Although many affected individuals have http://ebooksmedicine.net
Fig.21.39Rheumatoidarthritisofthehand.Characteristicfeaturesincludediffuseosteopenia,markedlossofthejointspacesofthecarpal,metacarpal,phalangeal,andinterphalangealjoints,periarticularbonyerosions,andulnardriftofthefingers.
chronic disease, only about 10% develop serious functional disability.
The spondyloarthropathies are a heterogeneous group of disorders that share the following features:
Absence of rheumatoid factor
Pathologic changes in the ligamentous attachments rather than synovium
Involvement of sacroiliac joints, with or without other joints
Association with HLA-B27
Bony proliferation leading to ankylosis (fusion of joints)
The manifestations are immune mediated and are triggered by a T cell response presumably directed against an undefined antigen, possibly infectious, that may cross-react with antigens expressed on cells of the musculoskeletal system.
Ankylosing spondylitis, the prototypical spondyloarthritis, causes destruction of articular cartilage and bony ankylosis, especially of the sacroiliac joints. The disease becomes symptomatic in the second and third decades of life as lower back pain and spinal immobility. Involvement of peripheral joints, such as the hips, knees, and shoulders, occurs in at least one-third of affected individuals. Approximately 90% of patients are HLA-B27 positive, but how the B27 allele contributes to the disease is not known. An antiIL-17 antibody has shown some efficacy in this disease.
Reactive arthritis is defined by a triad of arthritis, nongonococcal urethritis or cervicitis, and conjunctivitis. Most affected individuals are men in their 20s or 30s, and more than 80% are HLA-B27 positive. The disease is probably caused by an autoimmune reaction initiated by previous infection of the genitourinary system (Chlamydia) or the gastrointestinal tract (Shigella, Salmonella, Yersinia, Campylobacter). Within several weeks of urethritis or diarrhea, patients experience low back pain. The ankles, knees, and feet are affected most often, frequently in an asymmetric pattern. Patients with severe chronic disease have involvement of the spine that is indistinguishable from ankylosing spondylitis.
Joints can become infected from hematogenous dissemination, direct inoculation through the skin, or from contiguous spread from a soft tissue abscess or osteomyelitis. Infectious arthritis is potentially serious, because it can cause rapid, permanent joint destruction.