Epidemiological Studies

The occurrence of non-Hodgkin lymphoma is the most serious complication of SS. A higher risk for the development of lymphoma in these patients, reaching 6.4 cases per 1000 patients/year (44 times greater than in a normal population), was first described by Kassan et al. [15] in a prospective study. Since this initial epidemiological study, several authors have retrospectively analyzed the incidence of lymphoma in patients with SS (Table 1). The percentage of patients with SS who develop lymphoma varied in these studies from 1 to 10%. Potential explanations for this variation include differences in the criteria used for the diagnosis of SS and in the length of follow-up.

Patients with primary SS have the highest risk of developing lymphoproliferative disorders. None of the patients described by Kruize et al. [16] with isolated keratoconjunctivitis sicca or secondary SS had developed lymphoproliferative disease in a long-term follow-up study. Similarly, in another study of 331 Italian patients [17], no lymphoma was diagnosed in patients with secondary SS. A recent epidemiological study performed in Finland [18] showed a standardized incidence ratio of non-Hodgkin lymphoma of 2.2 for rheumatoid arthritis (RA), 4.5 for secondary SS and 8.7 for primary SS. Finally, patients with a younger onset of SS seem to be a higher risk for developing lymphoproliferative disorders. In a study by Kassan et al. [15], patients with an onset of SS before the age of 45 years had 60 times the incidence expected for developing lymphoma from the rate obtained in general population. Our recent studies [19) confirmed these data and showed a higher incidence of lymphadenopathy, rheumatoid factor, MIgs and lymphoma in SS patients with a disease onset before the age of 35.

Table 1. Incidence of lymphoma in patients with SS according to several authors







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