Background Previous observation has found that SLE patients with arthritis tended to have less renal involvement, and the presence of rheumatoid factor (RF) might protect against lupus nephritis (LN).

Objectives This study was performed to determine whether the presence of chronic arthritis (CA) protects against renal involvement or has less degree of nephritis in SLE patients.

Methods The medical records of SLE patients, who were followed-up at the Division of Rheumatology, Chiang Mai University, were reviewed. Patients with CA were classified as a “case”. Controls comprised SLE patients who were close to the case in hospital number, but had no chronic arthritis (NCA). The ratio of case to control was 1:2. SLE disease activity was determined by the modified SLE disease activity index-2000 (mSLEDAI-2K). The severity of SLE was ascertained by the sum of the Mexican SLEDAI score. Organ damage was detected by the Systemic Lupus International Collaborating Clinics/American College of Rheumatology (SLICC/ACR). Renal activity was determined by the SLICC Renal Activity/Response Exercise (SLICC/RARE).

Results There were 46 cases (45 females) and 92 controls (90 females) with a mean age of 44.35±14.09 years and 42.03±13.61 years, respectively, and mean disease duration of 9.44±7.47 years and 9.75±7.17 years, respectively. Twenty-eight patients in the CA group had chronic arthritis before SLE diagnosis was made with a mean duration of 2.06±2.34 years (median 1 year). There was no significant difference between the CA and NCA group in the mSLEDAI score (3.50±5.15 vs. 3.25±4.73), the cumulative MEX-SLEDAI score (9.52±5.55 vs. 11.24±5.14), and the SLICC/ACR score (1.15±1.15 vs. 0.90±1.24); but the number of ACR classification criteria was significantly higher in the CA group (5.46±1.52 vs. 4.78±1.11, p=0.009). The CA group, within the ACR classification criteria, had significantly more arthritis (100% vs. 47.82%, p<0.001), but less renal involvement (28.26% vs. 52.17%, p=0.008). There was no significant difference between the CA and NCA group in the prevalence of ANA (97.82% vs. 95.65%), anti-dsDNA (63.04% vs. 54.34%), anti-Sm (21.62% vs. 40.00%), anti-RNP (39.47% vs. 40.00%), anti-Ro (57.14% vs. 53.33%), anti-La (11.76% vs. 13.33%), and anti-cardiolipin antibodies (9.37% vs. 5.26%). Eleven patients (23.91%) in the CA group had positive RF (RF+). The time from the diagnosis of SLE to the onset of first LN was significantly longer in the CA group (10.24±7.43 months vs. 5.00±5.90 months, p=0.008). However, there was no significant difference between the CA and NCA group in the SLICC/RARE score (10.23±4.26 vs. 9.72±3.55), the maximum degree of 24-hour proteinuria (3.64±1.73 gm vs. 4.48±2.95 gm), and the maximum serum creatinine (1.50±1.05 mg/dL vs. 1.47±1.06 mg/dL) at first LN episode. Among the CA group, none of 11 cases with RF+ (0%), but 13 of 35 cases of those with RF- (37.14%) had renal involvement (p=0.02).

Conclusions Significantly fewer SLE patients with CA had renal involvement than those with NCA, but there was no difference in the renal activity between the two groups. CA with RF+ is a protective factor for renal involvement in SLE patients.

Disclosure of Interest None declared