Chronic arthritis in systemic lupus erythematosus: distinct features in 336 paediatric and 1830 adult patients.

The objectives of this study are to assess the frequency of chronic arthritis and compare the clinical and laboratory features in a large population of childhood-onset systemic lupus erythematosus (cSLE) and adult-onset (aSLE) patients. This historical study evaluated 336 cSLE and 1830 aSLE patients. Chronic arthritis was defined as synovitis of at least 6 weeks of duration. Rhupus was characterised as the association of SLE and chronic inflammatory arthritis with erosion and positive rheumatoid factor. Jaccoud's arthropathy is a non-erosive subluxation leading to severe deformity of the hands and feet. Data were compared using Student's t test or the Mann-Whitney test for continuous variables. For categorical variables, differences were assessed by Fisher's exact test and Pearson chi-square. Frequencies of chronic arthritis were similar in cSLE and aSLE (2.4 vs. 3.8%, p = 0.261). The median time from disease onset to appearance of chronic arthritis was shorter in cSLE (0 vs. 10 years, p < 0.001), and the median of age at chronic arthritis diagnosis was [10.8 (4.2-14.6) vs. 40 (21-67), p < 0.001]. The children presented with more chronic polyarthritis than the adults (75 vs. 32%, p = 0.024), a higher median number of joints with arthritis [8.5 (1-18) vs. 3 (1-9), p = 0.017] and a higher number of joints with limitation [1.5(0-24) vs. 0(0-4), p = 0.004]. The chronic arthritis diagnosis frequencies of hepatomegaly (25 vs. 0%, p = 0.009), splenomegaly (25 vs. 0%, p = 0.009), pericarditis (25 vs. 0%, p = 0.009), nephritis (37 vs. 3% , p = 0.006), haematuria (37 vs. 1.4%, p = 0.002), lupus anticoagulant (40 vs. 1.6%, p = 0.012), anticardiolipin IgM (40 vs. 1.5%, p = 0.012) and median Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) [10.5(1-20) vs. 6(4-16), p = 0.029] were higher in cSLE. Frequency of rhupus, (12 vs. 17%, p = 1.0), Jaccoud's arthropathy (0 vs. 17%, p = 0.343) and treatments were similar in cSLE and aSLE. We determined that chronic arthritis in SLE has distinct features in children, with very early onset, polyarticular involvement and association with active disease. We further demonstrated in this series that a proportion of chronic arthritis involvement in SLE is manifested as rhupus and Jaccoud's arthropathy.