Lymphoma in Sjögren's syndrome: urinary monoclonal free light chains as a diagnostic aid and a means of tumour monitoring.

Non Hodgkins lymphoma (NHL) is reported to be at least 40 times more common in Sjögren's syndrome (SS). Diagnosis may be difficult as blood and bone marrow haematology can remain normal, with no evidence of a serum paraprotein band or Bence-Jones proteinuria by routine electrophoresis. Using the technique of isoelectric focusing in agarose, followed by immunofixation, monoclonal free light chains can be found in the urine of 44% and 74% respectively of patients with NHL and B cell chronic lymphocytic leukaemia, but not in normal individuals. Three patients, two with typical severe primary SS and the third with several features of SS including abnormal sialography and reduced tear secretion, developed B cell NHL of parotid and/or lung. Using the above method on concentrated urine specimens, monoclonal free light chains of the same class as that demonstrated on the tumour cells were found to be present in each patient's urine. In one patient the level of urinary free light chains was monitored and found to correlate with disease activity. Using similar techniques no monoclonal light chains could be found in the urine from a further 10 cases of primary SS and 18 cases of SS secondary to rheumatoid arthritis, all of whom had no clinical evidence of lymphoma. Screening of SS patients' urine by the method described for monoclonal urinary free light chains may provide an early diagnostic clue to the development of lymphoma and be a means of tumour monitoring.