Subsets of Systemic Lupus Erythematosus

In the wide spectrum of clinical manifestations, different subsets of systemic lupus and clusters can be defined by clinical or serologic items. Relevant and established

Table 13.3. Typical autoantibodies in patients with systemic lupus erythematosus (SLE)

Autoantibody

Incidence (%)

Antigen Detected

Clinical Importance

Antinuclear

98

Multiple nuclear

Repeatedly negative test

antibodies

results make SLE unlikely

Anti-DNA

70

DNA (double stranded)

Anti-double-stranded DNA is disease specific, anti-single-stranded DNA is not; high titers are associated with clinical activity

Anti-Sm

30

Protein complexed to six species of small nuclear RNA

Specific for SLE

Anti-RNP

40

Protein complexed to U1RNA

High titer in syndromes with features of polymyositis, lupus, scleroderma, and mixed connective tissue disease; if present in SLE without anti-DNA, risk of nephritis is low

Anti-Ro/SSA

30

Protein complexed to y1-y5 RNA

Former "antinuclear antibody- negative" lupus, SLE, SCLE, Sjogren's syndrome, Sjogren/lupus overlap, neonatal lupus, congenital heart block; can be associated with nephritis (+ double-stranded DNA antibodies)

Anti-La/SSB

10

Phosphoprotein

Always associated with anti-Ro/SSA (risk for nephritis is low if present)

Antihistone

70

Histones

More frequent in drug-induced LE (95%)

Antiphospholipid

50

Phospholipids

Lupus anticoagulant, anticar-diolipin, and false-positive test result for syphilis; the two former (particularly high-titer IgG) are associated with thrombembolic complications (such as strokes) and fetal losses

autoantibodies of SLE are given in Table 13.3 (see also Chap. 24) (Elkon 1998). They can be divided into marker antibodies for diagnosis, for different subsets, and for disease activity. Clear positive ANAs in a standardized test (immunofluorescence) using the proper substrate (HEp-2 cells) are suitable as serologic screening for SLE, reaching a sensitivity of nearly 100%. However, as ANAs are also found in many other connective tissue diseases, their specificity is considerable low. Antibodies against ds-DNA are highly specific for SLE and have a rather strong (at least intraindividual)

correlation with disease activity and in high titers of high avid antibodies with lupus nephritis. Antibodies against different extractable nuclear antigens, like Ro/SSA-, La/SSB-, Sm-, and U1RNP, alone or in different combinations, seem to define more homogeneous disease entities. Their concentration proved not to be of considerable additional value for monitoring of the disease.

U1RNP Antibody-Positive Lupus

In 1972, Sharp et al. (Sharp et al. 1972) described a "mixed connective tissue disease" subset with clinical features of SLE, scleroderma, and polymyositis. Serologically, this group is defined by the occurrence of ANAs, with a coarse speckled pattern revealing anti-UlRNP specificity (without anti-Sm antibodies). Rheumatoid factors and hypergammaglobulinemia are often present. Nearly all patients demonstrate Raynaud's phenomenon, acrocyanosis, edematous sclerodactyly, telangiectasias, and other ery-thematous skin lesions (Schneider and Fischer 2000). Dysphagia due to disturbance of esophageal motility is a frequent symptom, and microstomia and pulmonary basal fibrosis are also indicative of overlapping scleroderma as inflammatory myopathy for polymyositis. Renal or cerebral involvement is very rare, but transition into SLE (with development of anti-Sm and anti-ds-DNA antibodies) is reported. The overall activity of disease and prognosis are rather favorable compared with full-blown lupus or a diffuse form of systemic sclerosis.

Sm Antibody-Positive Lupus

Anti-Sm antibodies are regarded as the most specific marker autoantibodies for SLE, indicating in addition severe forms of it. As such, it is part of the American College of Rheumatology (ACR) classification criteria, even though prevalence in SLE is about 10% in whites (and higher in blacks). Cerebral vasculitis and lupus nephritis are reported to be more frequent in patients with LE and anti-Sm antibodies (Craft 1992). Skin manifestations are from the ACLE type, with the classic butterfly rash, photosensitive erythematous skin lesions, and severe acral vasculitis with a tendency to atrophic scarring.

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