Patient characteristics
| Characteristics | SLE | pSS | Overlap | P value | |
| General features | Mean age at diagnosis, years (SD) | 33 (11.88) | 54 (13.96) | 41 (16.43) | p < 10-4 |
| Female, n (%) | 40 (81.6) | 49 (100) | 26 (100) | p = 0.001 | |
| SLEDAI,6 mean (SD) | 11.32 (7.20) – | – | 6.5 (5.34) | 0.002 | |
| Mean ESSDAI,5 mean (SD) | x | 5.55 (3.28) | 9.65 (5.43) | p = 0.001 | |
| Mean disease duration, years (SD) | 14.2 (8.8) | 14.4 (6.5) | 14 (5) | p = 0.748 | |
| Clinical features | Fever, n (%) | 9 (18.37) | 1 (2.04) | 3 (11.53) | p = 0.003 |
| Photosensitivity, n (%) | 9 (18.37) | 2 (4.08) | 4 (15.38) | p = 0.082 | |
| Acute/subacute lupus, n (%) | 22 (44.90) | 0 (0) | 4 (15.38) | p < 10-4 | |
| Chronic lupus, n (%) | 8 (16.32) | 0 (0) | 0 (0) | p = 0.001 | |
| Oral ulcerations, n (%) | 6 (12.24) | 2 (4.08) | 0 (0) | p = 0.083 | |
| Non-scarring alopecia, n (%) | 7 (14.29) | 0 (0) | 2 (7.69) | p = 0.024 | |
| Pleurisy, n (%) | 7 (14.29) | 0 (0) | 0 (0) | p = 0.003 | |
| Pericarditis, n (%) | 4 (8.16) | 0 (0) | 1 (3.84) | p = 0.121 | |
| Adenomegalies, n (%) | 10 (20.40) | 3 (6.12) | 5 (19.23) | p = 0.099 | |
| Myalgias, n (%) | 4 (8.16) | 14 (28.57) | 5 (19.23) | p = 0.034 | |
| Arthralgias, n (%) | 45 (91.84) | 41 (83.67) | 19 (73.08) | p = 0.097 | |
| Synovitis, n (%) | 26 (53.06) | 3 (6.12) | 8 (30.77) | p < 10-4 | |
| Cough, n (%) | 0 (0) | 12 (24.49) | 9 (34.61) | p = 0.0001 | |
| Biological features | Leukopenia*, n (%) | 9 (18.36) | 3 (6.12) | 4 (23.07) | p = 0.178 |
| Lymphopenia†, n (%) | 16 (32.65) | 7 (14.29) | 13 (50) | p = 0.004 | |
| Mean CRP, mg/L (SD) | 13.68 (28.13) | 9.32 (13.98) | 7.66 (15.22) | p = 0.0004 | |
| Immunological features | ANA >1/80 IIF **, n (%) | 48 (97.96) | 36 (73.47) | 25 (96.15) | p = 0.003 |
| Anti-DNA, n (%) | 44 (89.80) | 0 (0) | 26 (100) | p < 10-4 | |
| Anti-Sm, n (%) | 19 (38.77) | 0 (0) | 7 (26.92) | p < 10-4 | |
| RF positivity, n (%) | 1 (2.04) | 17 (34.69) | 11 (42.30) | p = 0.001 | |
| APL, n (%) | 20 (40.82) | 7 (14.28) | 7 (26.92) | p = 0.013 | |
| Hypocomplementaemia C3 ‡, n (%) | 13 (26.53) | 0 (0) | 3 (11.54) | p < 10-4 | |
| Hypocomplementaemia C4§, n (%) | 24 (48.98) | 9 (18.36) | 9 (34.6) | p = 0.006 | |
| Hypergammaglobulinaemia ¶, n (%) | 18 (58.06) | 21 (43.75) | 22 (88.46) | p = 0.0002 | |
| Mean serum gammaglobulin level, g/L (SD) | 15.4 (5.44) | 14.3 (6.44) | 19.1 (6.58) | p = 0.002 | |
| Renal features | Significant glomerular proteinuria, n (%) | 17 (34.69) | 0 (0) | 1 (3.85) | <10−4 |
| Sets of criteria | SLE ACR-1997, n (%) | 38 (77.6) | 1 (2.1) | 10 (38.5) | p < 10-4 |
| SLE SLICC, n (%) | 48 (97.9) | 4 (8.3) | 20 (76.9) | p < 10-4 | |
| 2019 SLE EULAR/ACR, n (%) | 48 (97.9) | 2 (4.2) | 22 (84.6) | p < 10-4 | |
| pSS ACR/EULAR 2016, n (%) | 0 (0) | 49 (100) | 26 (100) | p=1.000 | |
Significant glomerular proteinuria was defined by daily proteinuria ≥1 g/day.
*Leucopenia was defined by leucocyte count <4 x109/L
†Lymphopaenia was defined by lymphocyte count <1x109/L.
‡Hypocomplementaemia C3 was defined by seric C3 fraction level ≤0.5 g/L.
§Hypocomplementaemia C4 was defined by seric C4 fraction level ≤0.15 g/L.
¶Hypergammaglobulinaemia was defined by serum gammaglobulin level >13.5 g/L.
ACR, American College of Rheumatology; ANA, antinuclear antibodies;APL, antiphospholipid; CRP, C reactive protein; ESSDAI, EULAR Sjögren’s syndrome Disease Activity Index;EULAR, European League Against Rheumatism; IFF, indirect immunofluorescence assay; pSS, primary Sjögren’s syndrome; RF, rheumatoid factor ; SLE, systemic lupus erythematosus; SLEDAI, Systemic Lupus Erythematosus Disease Activity Index; SLICC, Systemic Lupus International Collaborating Clinics.