Urinary monoclonal free light chains in primary Sjögren's syndrome: an aid to the diagnosis of malignant lymphoma.

Three patients, two with typical primary Sjögren's syndrome (SS) and the third with several features of SS, including abnormal sialography and reduced tear secretion, developed B cell non-Hodgkin's lymphoma (NHL) of parotid or lung, or both. Isoelectric focusing of concentrated urine specimens in agarose, followed by immunofixation, demonstrated the presence in each patient's urine of monoclonal free light chains of the same class as that shown on the tumour cells. In one patient the level of urinary free light chains was monitored and found to correlate with disease activity. Similar techniques showed no monoclonal light chains in the urine from a further 26 cases of SS with no clinical evidence of lymphoma. The detection of monoclonal urinary free light chains may provide an early diagnostic clue to the development of lymphoma in patients with SS and be a means of tumour monitoring.