Monoclonal gammopathy related to Sjögren syndrome: a key marker of disease prognosis and outcomes.

OBJECTIVE: 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.
METHODS: 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.
RESULTS: 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).
CONCLUSION: 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).