SYSTEMIC LUPUS ERYTHEMATOSUS
Systemic lupus erythematosus (SLE) represents the prototype of autoimmune disease, with the presence of autoantibodies as its hallmark. The incidence of SLE diagnosed in patients younger than age 16 is approximately 0.25 to 11 new cases per 100,000 annually, with an overall prevalence of 1.89 to 63.1 per 100,000 depending on ascertainment and ethnicity of the population. The prevalence and incidence rates are higher in the 12- to 18-year age group. Both the incidence and prevalence rates are 2.4 to 4.9 times higher in African Americans, Native Americans, Asians, Southeast Asians, and Hispanics compared with white children. The female predominance (4–5:1) in pediatric patients is lower than that in adults (9:1), although some but not all studies suggest that the female-to-male ratio may vary in different ethnic populations. The mean age at diagnosis is approximately 12 to 13 years, but presentation of patients as young as age 5 years is routinely reported, and the age of onset varies by ethnicity, with nonwhite populations tending to have onset of disease at younger ages. Presentation prior to age 3 to 5 years is frequently associated with a genetic defect. Despite significant improvements in the outcome of childhood-onset SLE (cSLE), mortality rates remain substantial, with a United Kingdom study reporting standardized mortality ratios (compared to national statistics in the general population) as high as 18.3 for all cSLE and 87 for those with SLE onset at <10 years of age (however, the confidence intervals were wide).
Neonatal lupus erythematosus (NLE) must not be mistaken for early-onset SLE. NLE is a disease caused by the transplacental passage of maternal autoantibodies, and the fetus/neonate has a normal immune system that is not actively producing autoantibodies. A minority of these children develop true SLE many years later. In contrast, cSLE is a disease in which the child produces autoantibodies and the immune abnormalities are intrinsic to the child’s immune system.
SLE, similar to most autoimmune diseases, is the result of a combination of genetic and environmental factors leading to the clinical and laboratory phenotype. The reported environmental risk factors include viral infections, estrogens, cigarette smoke, pesticides, and sunlight. The mechanism leading to the production of autoantibodies, the hallmark of SLE, is the break of tolerance of self-antigens. It is theorized that increased/abnormal apoptosis, necrosis, autophagy, or netosis leads to the decreased clearance of self- or viral dsDNA and ssRNA. This clearance, in turn, stimulates autoreactive T and B cells, leading to the production of autoantibodies and proinflammatory cytokines, resulting in tissue damage. The autoantibodies usually are directed against histone, nonhistone, RNA-binding, cytoplasmic, and nuclear proteins. However, more than 100 different autoantigens have been described to date. Antinuclear antibodies (ANAs) occur in most patients, but ANA-negative SLE does occur. ANA-negative SLE usually is seen in patients having only anti-Ro antibodies and is an artefact of the immunofluorescent testing for ANA. Anti-DNA antibodies are present in approximately 50% to 60% of patients, whereas antibodies directed against the ...