Objectives: To investigate if indicators of a heavier involvement of mucosa-associated lymphoid tissue (MALT) in primary Sjögren's syndrome (pSS), i.e. persistent salivary gland (SG) swelling and cryoglobulinaemia, might better evaluate the lymphoma risk compared to the ESSDAI. Therefore, the current concept of disease activity of pSS should be re-evaluated, based solely on ESSDAI.
Methods: A cohort of 255 pSS patients, including 30 pSS with B-cell lymphoma, was investigated. Three subgroups were distinguished, i.e. pSS developing lymphoma in the follow-up (n=12), pSS with lymphoma at cohort inclusion (n=18), and control pSS not developing lymphoma in the follow-up (n=225). SG swelling, cryoglobulinaemia and ESSDAI were evaluated at baseline, in the follow-up to one year before lymphoma diagnosis, and at lymphoma diagnosis.
Results: SG swelling and/or cryoglobulinaemia at baseline were significantly higher (p=0.0003) in pSS patients evolving into lymphoma if compared to pSS controls, while ESSDAI showed no significant difference. Both SG swelling and cryoglobulinaemia persisted and sometimes developed ex novo in the follow-up. SG swelling and cryoglobulinaemia were present in 24/30 (80%) cases the time of lymphoma diagnosis, and lymphoma itself was usually of MALT/marginal zone histotype (90%), leading to peculiar manifestation of lymphoma in pSS.
Conclusions: The autoimmune and lymphoproliferative involvement of MALT is the biological substrate of pSS. If this involvement is heavier, as reflected by SG swelling and cryoglobulinaemia, disease activity may be considered higher, and the risk of lymphoma is increased. The current concept and evaluation of activity of pSS, based solely on the ESSDAI, needs revision.