Background/Purpose: Mixed connective disease is a multi-system disorder with overlapping features of SLE, rheumatoid arthritis, scleroderma and polymyositis/dermatomyositis with high titres of U1 RNP. Arthritis is a common manifestation that can be erosive and deforming. However, it is unclear whether clinical arthritis in MCTD is more common than SLE and there is little data comparing detection of synovitis by ultrasound in the two diseases.

Methods: In this cross-sectional study, we used the Kasukawa criteria for the diagnosis of MCTD and SLICC criteria for SLE patients. Patients were matched for gender and disease duration. U1-RNP was done in MCTD patients by Fluorescence Enzyme Immuno Assay in a 1:10 dilution and ANA by ELISA with a 1:200 dilution of sera. History of arthralgia/arthritis and clinical evaluation for swelling, tenderness, limitation of movements and deformities was done. Functional disability was assessed using the Indian Health assessment questionnaire.Hand radiographs of patients were assessed by for erosions. In addition, ultrasound (9-14 Mhz linear probe) of the non-dominant wrist, metacarpal joints for synovitis and teno-synovitis of flexor and extensor wrist compartments was assessed using the OMERACT definition.

Results: Forty patients were recruited in both groups, with similar gender distribution (F:M=38/2, 38/2), disease duration (3.7±2.3, 4.7±3.1, p=0.1) but slightly younger in age (31.8±13.3, 36±10.2, p=0.01) in MCTD than SLE. ANA was positive in all patients in both groups, and U1RNP was positive in all MCTD patients .History suggestive of inflammatory arthralgia/arthritis (100 vs 75%, p = 0.001) and current arthritis on examination (65 vs 37.5%, p=0.03) was significantly higher in MCTD than SLE (Table 1). PIP (30 vs 10%, p=0.025) and wrist (61.8vs 32.5%, p =0.007) involvement were significantly more in the MCTD. (Table 1) Use of methotrexate was also significantly more in the MCTD group(20% vs 5% p= 0.043). However, on Ultrasound there was no significant difference in presence of synovitis (p= 0.32) or teno-synovitis (p=0.51) and there was no difference in the functional disability measured by Indian Health assessment questionnaire (0.73 vs 0.74, p=0.7).Deformity was more common in MCTD (10 vs 0%), however, erosions were uncommon in both.Rheumatoid factor was positive more in patients with MCTD than SLE (34.4 vs 6.3%, p=0.005)

Conclusion: In this study we observed clinical arthritis to be significantly higher in MCTD patients in comparison with SLE, however, an equally high presence of synovitis on Ultrasound.

Table 1: clinical arthritis

ACR Meeting Abstracts - https://acrabstracts.org/abstract/mixed-connective-tissue-disorder-has-higher-prevalence-of-arthritis-and-use-of-methotrexate-than-systemic-lupus-erythematosus/