28.1Antinuclear Antibodies

sis of systemic autoimmune diseases [1, 9]. Low titers are less significant than high titers [10]. Although positive ANA assays were not included in the 2002 Classification Criteria for SS, their role in the diagnosis of patients with suspected SS should be reconsidered for various reasons. First, ANA are the most frequently detected antibodies in primary SS, and their determination play a central role in differentiating SS from causes of sicca syndrome that do not relate to autoimmunity. Second, ANA were associated with various extraglandular and serological features of SS [11–13], including hypergammaglobulinemia, elevations in the erythrocyte sedimentation rate, and autoantibodies directed against extractable nuclear antigens (ENAs) [14]. Third, ANA titers ³ 1/80 have an excellent positive predictive value (91%) for the classification of patients with primary SS according to the 2002 Criteria. Thus, a patient with xerostomia, xerophthalmia, positive ocular tests, positive parotid scintigraphy, and an ANA titer ³ 1/80 should be classified as having primary SS, even in the absence of anti-SSA/Ro and anti-SSB/La antibodies, assuming the absence of a coexisting systemic autoimmune disease.

28.2Anti-SSA/Ro and Anti-SSB/La Antibodies

ENAs are a heterogeneous group of ribonucleoproteins and nonhistone proteins that mediate different functions in nuclear metabolism. Anti-SSA/Ro, -SSB/La, -RNP, and -Sm autoantibodies are directed against small ribonucleoproteins, which are small constituents of cellular RNA [15].

Four molecular forms of the autoantigen Ro complex have been described: a Ro-lymphocyte peptide of 60 kDa, a Ro-erythrocyte peptide of 60 kDa peptide, a Ro-lymphocyte peptide of 52 kDa peptide, and a Ro-erythrocyte peptide of 54 kDa. The Ro complex is found in most tissues and cells (erythrocytes, platelets), with differences in structure and quantity across tissues, species, and embryonic development stages. The great majority of patients with primary SS have antibodies against the SSA/Ro or SSB/La antigens [16], and there is a close correlation between these autoantibodies and certain clinical features, including parotidomegaly [17, 18], lymphadenopathy [17], cutaneous vasculitis [18–21], neurologic disease [18–20], a focus score higher than 1 in salivary gland biopsy [12, 22], and serologic hallmarks such as the presence of hypergammaglobulinemia [17, 18, 21, 23], rheumatoid factor [18], and cryoglobulins [18]. Locht et al. [24] reported that the presence of anti-SSA/Ro and anti-SSB/La antibodies was a stronger predictor of internal organ involvement than was the presence of anti-SSA/Ro antibodies alone.

Although antibodies to the SSA/Ro and SSB/La antigens are characteristic of the most clinically and immunologically “active” subset of patients with primary SS, their use as mandatory criteria for primary SS would lead to the exclusion of some subsets of patients who are usually Ro/La negative (e.g., males, the elderly, and patients without extraglandular features) [16].

28.3Antibodies Against Nonnuclear Antigens

In contrast to ANA, the clinical significance of antibodies directed against nonnuclear antigens has been little studied in primary SS. Nonnuclear antigens that are potentially relevant to systemic autoimmune conditions include antimitochondrial antibodies and anti-parietal cell antibodies, but an extensive list of other antibodies have also been investigated.

In 2006, the prevalence and clinical significance of these autoantibodies was studied in a large cohort of patients [25]. A variety of important observations were made. First, these antibodies are detected in primary SS at very different frequencies. As examples, anti-smooth muscle antibodies were detected most frequently. Anti-parietal cell antibodies were detected as often as were anti-SSB/La antibodies, but anti-LKM-1 antibody assays were negative in all patients. Despite the frequency of anti-parietal cell antibodies in SS, chronic atrophic gastritis and pernicious anemia are rare in this condition, being reported in only 2 of 380 patient in one study [26] and in less than a handful of other reports in the literature [27–29].

Second, the clinical significance of these autoantibodies directed against nonnuclear antigens differs from that of antibodies whose targets are nuclear antigens. In contrast to ANA, which are closely associated with extraglandular and laboratory features of SS, antibodies directed against nonnuclear antigens are mainly associated with organ-specific autoimmune diseases, particularly those associated with liver and thyroid autoimmune disease. However, it is important to note that many SS patients whose sera have autoantibodies “specific” for autoimmune liver or thyroid disease have no clinical evidence of dysfunction in these organs.

Third, there is a small subset of patients with primary SS and positive antimitochondrial antibodies (AMA) (8%), an immunological marker closely related to primary biliary cirrhosis (PBC) [30]. However, only 50% of our SS patients who had AMA demonstrated clinical or laboratory test evidence of liver disease. This suggests the existence of an incipient or incomplete PBC in some patients with primary SS.

28.4Anti-DNA Antibodies

Few studies have analyzed the clinical significance of anti-DNA antibodies in patients with primary SS. Satoh et al. [7] described an elderly woman with primary SS who presented anti-Sm and anti-DNA antibodies prior to the development of systemic lupus erythematosus (SLE). Zufferey et al. [6] described the occurrence of SLE in two out of four primary SS patients in whom anti-DNA antibodies were detected between 2 and 11 years after the diagnosis of primary SS. In a study of 26 patients with primary SS who had anti-DNA autoantibodies [31], features of SLE included ANA positivity in all cases, leukopenia in 14 (54%), and articular involvement in 9 (35%). Other SLE features such as skin, renal, and central nervous disease were uncommon. After a median follow-up of nearly 6 years, 8 (31%) of the 26 SS

patients with anti-dsDNA antibodies at baseline fulfilled 4 or more of the classification criteria for SLE and 10 (38%) fulfilled 3 criteria.

Manoussakis et al. [32] described the clinical characteristics of 26 patients with coexistence of SS and SLE. In comparison to patients with SLE, the SS-SLE patients were older and had a higher frequency of certain features (Raynaud’s phenomenon, rheumatoid factor, and anti-SSA-Ro/SSB-La antibodies) but a lower frequency of others (glomerulonephritis and thrombocytopenia). Autoantibodies were not useful in distinguishing between SLE and SS-SLE patients. The clinical presentations of the two patient groups were similar. The substantial overlap in the clinical and serologic features of primary SS and SLE, and the consequent difficulties in using classification criteria to distinguish between them have been emphasized [33]. Thus, there seems to be a fine line separating primary SS and SS-SLE in patients older than 50 years [33, 34], since the main SLE-related features found in SS-SLE patients (ANA, articular involvement, and cytopenias) are also frequently found in primary SS [17, 27, 35–37]. Because some SS-DNA patients develop overlapping SLE over time, we suggest including anti-DNA antibodies in the immunological follow-up of patients with primary SS, especially in those with articular involvement or leukopenia.

28.5Anti-Sm Antibodies

Anti-Sm antibodies are rarely found in patients with primary SS. To date, only nine cases are reported in the literature [6, 7, 31]. After a mean follow-up of nearly 5 years, the previously reported three SS-Sm patients developed SLE, while five out of our six SS-Sm + patients [31] presented an SLE-like disease with the fulfillment of three criteria (four presented cytopenia and one arthritis in addition to the two immunological criteria, ANA and anti-Sm). All nine SS-Sm patients had negative anti-DNA antibodies. These studies suggest that anti-Sm antibodies are an infrequent immunological event, and thus we do not recommend including anti-Sm antibodies in the routine immunological follow-up of patients with primary SS. However, we recommend a close follow-up of patients with primary SS with positive Sm antibodies, in order to detect clinical and/or analytical data suggesting the development of an additional systemic autoimmune disease, and thus, an evolution from a single autoimmune disease (primary SS) to an overlap syndrome (SS associated with SLE).

28.6Anti-RNP Antibodies

A small number of patients with primary SS have anti-RNP antibodies (<2% of patients). In one study of eight anti-RNP antibody-positive patients who had primary SS, none fulfilled the classification criteria for mixed connective tissue disease (MCTD) [31]. However, some patients demonstrated various components of these criteria, such as Raynaud’s phenomenon or synovitis. Several studies have analyzed