Discussion
Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by immune dysregulation resulting in the production of antinuclear antibodies (ANA), generation of circulating immune
complexes, and activation of the complement system. SLE has unpredictable exacerbations and remissions and a predilection for clinical involvement of the joints, skin, kidney, brain, serosa, lung,
heart, and the gastrointestinal tract. The pathologic hallmark of the disease is that it is recurrent, widespread and produces diverse vascular lesions. The health status of a patient with SLE is
related not only to disease activity, but also to the damage that results from recurrent episodes of disease flare (i.e. deforming arthropathy, shrinking lung, end stage renal disease, organic mental
syndrome, etc.), as well as the adverse effects of treatment (i.e. avascular necrosis of the bone, infections, precocious atherosclerosis, etc.). SLE is not a rare disorder. Although reported as
occurring at both the extremes of life (i.e. diagnosed in infants as well as in the tenth decade of life), it chiefly affects women of child bearing age with a female-to-male ratio of 9:1. The ethnic
group at greatest risk is the African Caribbean blacks. The annual incidence of SLE ranges from six to 35 new cases per 100,000 people in relatively low-risk to high-risk groups. The etiology of SLE
remains unknown. A genetic predisposition, sex hormones, and environmental trigger(s) likely result in the disordered immune response that typifies the disease. A role for genetics is suggested by
the increased percentage of two histocompatibility antigens in patients with SLE, HLA-DR2 and HLA-DR3. In addition, there is an increased frequency of the extended haplotype HLA-A1, B8, DR3. The role
for heredity is further supported by the concordance for this illness among monozygotic twins. The polygenic nature, however, of this genetic predisposition as well as the contribution of
environmental factors is suggested by the only moderate concordance rate which is reported to be between 25% and 60%. The origin of autoantibody production in SLE is unclear, but a role has been
suggested for an antigen driven process, spontaneous B-cell hyper-responsiveness, or impaired immune regulation. Regardless of the etiology of autoantibody production, SLE is associated with the
impaired clearance of circulating immune complexes secondary to decreased CR1 expression, defective Fc receptor function, or deficiencies of early complement components such as C4A. More is known
about the pathogenic cellular and molecular events which are responsible for vascular lesions in SLE than the origins of autoimmunity. Disease manifestations result from recurrent vascular injury due
to immune complex deposition, leukothrombosis or thrombosis. Additionally, cytotoxic antibodies can mediate autoimmune hemolytic anemia and thrombocytopenia, while antibodies to specific cellular
antigens can disrupt cellular function. An example of the latter is the association between anti-neuronal antibodies and neuropsychiatric SLE. The clinical features of SLE are protean and may mimic
infectious mononucleosis, lymphoma or other systemic disease. Initial clinical manifestations most frequently include constitutional symptoms and signs (malaise, weakness, fever, anorexia and weight
loss) and, articular (polyarthritis) and cutaneous (skin rash) findings. Characteristic and significant musculoskeletal abnormalities in patients with SLE may include myositis, symmetric
polyarthritis, deforming non-erosive arthropathy, subchondral cysts, spontaneous tendon weakening and rupture, osteonecrosis, soft tissue calcification, osteomyelitis, septic arthritis and other
miscellaneous abnormalities. Joint symptoms and signs are of variable severity and are most frequent in the small joints of the hand, knee, wrist and shoulder. On radiographs, soft tissue swelling
and periarticular osteoporosis are observed; instead, cartilage and bone destruction is rare. The deforming non-erosive arthropathy usually causes little functional disability and is completely
reducible, although some patients develop chronic fixed deformities. Swan neck deformity, boutonniere deformity and hallux valgus can also be seen. In the joints, capsular and ligamentous laxity,
contracture and muscular imbalance lead to abnormalities that are similar to those occurring in patients with rheumatic fever. Typically, there are ulnar deviation and flexion deformities of the
metacarpophalangeal joints that may be combined with hyperextension at interphalangeal joints. In the foot, fibular deviation and subluxation at metatarsophalangeal joints can be observed.
Spontaneous rupture of tendons, especially the Achilles, quadriceps and patellar tendons, takes place almost exclusively in patients who have been given systemically or locally administered steroids.
Osteonecrosis typically involves the femoral head but may also affect the humeral head, femoral condyles, tibial plateau, talus, and even the small bones of the hand, the wrist and the foot.
Administration of steroids is suspected to be the cause in many cases. Patients with SLE exhibit an unusually high frequency of bacterial and mycotic infections. On radiographs, the presence of a
large or increasing joint effusion and progressive cartilaginous and osseous destruction should raise the possibility of articular infection. Insufficiency fractures may also occur, with a
distribution similar to that in rheumatoid arthritis. MRI could help more, when compared to conventional radiography, in the precocious detection of this pathology showing characteristic signs of
soft tissue pathology (i.e. capsular swelling, edematous and proliferative tenosynovitis, synovial hypertrophy) and bony alterations (i.e. erosions, some of which are undetected by conventional
radiography).