To analyze the monoclonal expression of SS through the detection of serum monoclonal immunoglobulins (mIgs) in a large series of patients with Sjögren syndrome (SS), focusing on the etiology, characterization and evolution of the monoclonal band and the association with SS clinical expression and outcomes.
Serum immunoelectrophoresis (IE) was performed to 408 consecutive patients who were evaluated by our unit between 1992 and 2011: 221 patients who fulfilled the 2002 American-European criteria for primary SS, 122 primary SS patients who fulfilled exclusively the 1993 European criteria and 65 patients with SS-associated hepatitis C virus infection. IE was performed at diagnosis and every year during the follow-up.
Of the 221 patients with primary SS, 48 (22%) had monoclonal gammopathy. In the control groups, the prevalence was 16% in patients with SS who fulfilled the 1993 criteria (p > 0.05) and 52% in SS-HCV patients (p < 0.001). Monoclonal bands were characterized in 47/48 patients with primary SS: IgG (n = 21), IgM (n = 16), IgA (n = 5) and free light chains (n = 5); the light chain was κ in 28 patients and λ in 19 (κ:λ ratio 1.5). Primary SS patients with monoclonal gammopathy had a higher prevalence of parotidomegaly (38% vs 20%, p = 0.021), vasculitis (21% vs 6%, p = 0.003), neurological involvement (42% vs 23%, p = 0.016), higher mean values of circulating gammaglobulins (23.4 vs 20.6%, p = 0.026), ESR (56.6 vs 37.6 mm/h, p = 0.003), a higher prevalence of RF (69% vs 50%, p = 0.022), low C3 levels (24% vs 11%, p = 0.028), low C4 levels (24% vs 7%, p = 0.003), low CH50 activity (28% vs 11%, p = 0.008) and cryoglobulins (23% vs 8%, p = 0.012) compared with those without monoclonal gammopathy. Of the 48 patients with primary SS and monoclonal gammopathy, 8 developed hematologic neoplasia after a mean follow-up of 10 years, a higher prevalence than observed in patients without monoclonal gammopathy (17% vs 5%, p = 0.009). Survival rates according to the presence or absence of monoclonal gammopathy were 83% and 97%, respectively (log rank 0.004).
Monoclonal gammopathy was detected in 22% of patients with primary SS fulfilling the 2002 criteria, with mIgGκ being the most frequent type of band detected. In HCV-associated SS patients, the prevalence was higher (52%) with IgMκ being the most prevalent band detected. Monoclonal gammopathy was associated with a higher prevalence of parotid enlargement, extraglandular features, hypergammaglobulinemia, cryoglobulinemia and related markers (rheumatoid factor, hypocomplementemia), and with a poor prognosis (development of neoplasia and death).