Mixed connective tissue disease with juvenile onset: results of a retrospective single-center study
Authors: Kaleda M. I. , Nikishina I. P. , Latypova A. N. , Yudkina N. N. , Verizhnikova Zh. G. , Shapovalenko A. N. , Pachkoria T. N. 
Published: February 2024

Mixed connective tissue disease (MCTD) is one of the very rare systemic autoimmune diseases; it accounts for 0.1–0.6% of cases in pediatric rheumatologists' practices. MCTD is characterized by a broad spectrum of clinical manifestations and a high frequency of extremely unspecific symptoms at the onset, with the overall picture of the disease forming slowly and gradually. The diagnosis is often delayed and confirmed only at an advanced stage of organ dysfunction with the development of irreversible changes.Objective: to identify a group of patients fulfilling the criteria for MCTD in an open, single-center, continuous retrospective study among anti-ribonucleoprotein (anti-RNP) antibody-positive patients and to analyze their demographic, clinical and laboratory characteristics and therapy.Material and methods. All anti-RNP-positive patients admitted to the pediatric department of V.A. Nasonova Research Institute of Rheumatology from 2019 to 2023 and meeting at least one of the variants of the MCTD criteria (Kasukawa, Alarcуn-Segovia, Kahn and Sharp criteria) were included in the study.Results and discussion. 18 (56.25%, 17 girls and 1 boy) of 32 anti-RNP-positive patients fulfilled criteria for MCTD. Patients most frequently fulfilled a combination of criteria – Sharp and Kahn (n=8) or Alarcуn-Segovia and Kahn (n=8). The median age of onset of MCTD was 12.2 [9.7; 13.9] years. The most common clinical manifestations were arthritis (100%), various skin lesions (94.4 %), Raynaud's phenomenon (88.9%), lymphadenopathy (72.2%) and general constitutional disorders (50%). Sjögren's syndrome (SS) was diagnosed in 17 (94.4%) patients. All patients had antinuclear factor (ANF) 1/1280, and the anti-RNP level was >200 U/ml. There were also antibodies against double-stranded DNA (n=5), Ro- (n=4) and Sm- (n=5) antigens. An IgM rheumatoid factor was detected in 6 patients and hypergammaglobulinemia in 10 patients. Capillaroscopic changes in the nailfold with predominant scleroderma type were found in 77.8% of patients. The most common combination was of Raynaud's phenomenon, arthritis, SS, lymphadenopathy and hypergammaglobulinemia (50%). All patients received glucocorticoids, 9 – hydroxychloroquine, 8 – methotrexate, 3 – mycophenolate mofetil, 1 – cyclophosphamide, 1 – azathioprine. Biologic DMARDs (bDMARDs) were prescribed to 12 (66.7%) patients: 3 – rituximab, 8 – abatacept, 1 – belimumab, with an acceptable safety profile and initial efficacy.Conclusion. Most patients in the study met the Kahn criteria. Only 2 patients met all variants of the criteria, which indicates the need to use a combination of criteria when a MCTD is suspected. A combination of Raynaud's phenomenon, arthritis, SS, lymphadenopathy and hypergammaglobulinemia was observed in half of patients with MCTD. The presence of Raynaud's phenomenon and high ANF titer in children with rheumatic diseases, especially with a polymorphic clinical picture, requires the inclusion of MCTD in differential diagnosis. Preliminary results indicate the safety of the use of biologic drugs in children with MCTD.