We conducted the current study to analyze the prevalence and clinical significance of circulating monoclonal
immunoglobulins in patients with Sjögren syndrome (SS), focusing on the association with extraglandular features,
immunologic markers, hematologic
neoplasia, and hepatitis C virus (HCV)
infection. We performed serum immunoelectrophoresis in 200 patients with primary SS and 37 patients with HCV-related SS. All patients fulfilled 4 or more of the 1993 European classification criteria for SS.Of the 200 patients with primary SS, 35 (18%) presented circulating monoclonal
immunoglobulins. The monoclonal bands identified were 20
IgG (13 kappa, 7 lambda), 10
IgM (5 kappa, 5 lambda), 2 IgAkappa, and 3 free circulating light chains. Of the 37 SS-HCV patients, 16 (43%) had circulating monoclonal
immunoglobulins. The monoclonal bands identified were 10 IgMkappa, 5 IgGlambda, and 1 free light lambda chain. Compared with primary SS patients, SS-HCV patients presented a higher frequency of monoclonal
immunoglobulins (43% vs 18%, p = 0.001), with monoclonal IgMkappa being the most frequent monoclonal band. Six (12%) of the 51 SS patients with circulating monoclonal
immunoglobulins presented hematologic
neoplasia, compared with 3 (1.6%) of those without monoclonal
immunoglobulins (p = 0.004; odds ratio = 8.13; 95% confidence intervals, 1.64-51.54). In 2 of the 6 patients with monoclonal
immunoglobulins and
lymphoproliferative disorders, a change of the monoclonal component was detected in previous immunoelectrophoresis determinations before the development of hematologic
neoplasia. Circulating monoclonal
immunoglobulins were detected in nearly 20% of patients with primary SS, with monoclonal
IgG being the most frequent type of
immunoglobulin detected. In SS-HCV patients, the prevalence of monoclonal
immunoglobulins was higher (43%), with monoclonal
IgM being the most frequent type found. SS-HCV patients presented a more restrictive monoclonal expression (limited to either monoclonal IgMkappa or monoclonal IgGlambda) than primary SS patients, who showed all types of heavy and light chains.