Statistical evaluation of different clinical and serological parameters for the diagnosis of Sjögren's syndrome

The potential value for the diagnosis of Sjögren's syndrome (SS) of 28 clinical and 18 serological parameters was evaluated in 38 patients with primary (1 degree) SS, 29 with rheumatoid arthritis (RA), 30 with systemic lupus erythematosus (SLE), and 22 with mixed cryoglobulinemia (MC), by means of a stepwise discriminant analysis. Twelve patients with RA, 11 with SLE, and 8 with MC had evidence of sicca syndrome and were then classified as having a secondary (2 degree) SS. When comparing the various disease groups to each other, it was always possible to select different combinations of clinical and serological variables which defined highly significant discriminant functions. In addition, some parameters appeared to have a stronger discriminant power between different disease groups. For instance, 1 degree SS was well discriminated from RA by anti-Ro antibodies (Ab) and normal C-reactive protein (CRP) levels, from SLE by normal complement levels and the positivity of rheumatoid factor, from MC by the absence of liver involvement and normal complement levels. While anti-La Ab had the highest value in differentiating patients with 1 degree from those with 2 degrees SS, anti-Ro Ab and recurrent parotid swelling seem to be typical features of patients with SS with respect to those with other connective tissue disease but without sicca syndrome.