In a nationwide Japanese retrospective cohort of 249 patients strictly meeting the 2019 MHLW MCTD criteria, mixed connective tissue disease showed marked clinical heterogeneity, and severity classification was not associated with off-scale-high anti-U1-RNP antibody status or broad phenotypic categories, supporting rigorous cardiopulmonary screening and management tailored to the dominant clinical phenotype.
The study cohort of 249 patients strictly meeting the 2019 Japanese MHLW MCTD diagnostic criteria was drawn from a registry of 311 clinically diagnosed patients and was predominantly female.
All patients had Raynaud's phenomenon and/or swelling of the fingers or dorsum of the hands.
The most frequent phenotypic pattern was an overlap of SLE-like and SSc-like features, and about one third of patients had features across all three phenotypic domains.
Major organ involvement occurred in about one third of patients, with pulmonary arterial hypertension in 12.8%.
About 28.7% of evaluable patients were classified as having severe disease.
Off-scale-high anti-U1-RNP antibody status was not associated with severity classification or with broad phenotypic categories.
Most patients received glucocorticoids and over half received immunosuppressive agents.
The authors conclude that MCTD is markedly clinically heterogeneous and that findings support rigorous cardiopulmonary screening and phenotype-tailored management.
This study looked back at medical records of 249 people in Japan with mixed connective tissue disease (MCTD), a rare autoimmune condition that combines features of lupus, scleroderma, and inflammatory muscle disease. Most patients were women, with disease typically starting around age 40. All had Raynaud's phenomenon (fingers changing color in the cold) and/or swollen fingers or hands. The most common pattern was a mix of lupus-like and scleroderma-like features, and about a third had features of all three conditions. About one in three patients had involvement of a major organ, and about one in eight had pulmonary arterial hypertension (high blood pressure in the lung arteries). Roughly 29% of evaluable patients were classed as severe. Two-thirds were treated with glucocorticoids and over half with immunosuppressive drugs. Having a very high level of the anti-U1-RNP antibody, a hallmark of MCTD, did not predict whether disease was classed as severe, nor did the broad type of symptom pattern. This research suggests MCTD varies widely from person to person and that antibody level alone may not indicate how severe it is. The authors point to the importance of careful heart and lung screening and of treatment matched to each patient's dominant features. As a retrospective study, it shows associations and cannot establish cause.
Kubo S, Kanda Y, Kameda H, Kuwana M, Narazaki H, Fujii T, et al.. (2026). Clinical characteristics and severity classification in mixed connective tissue disease: a nationwide retrospective study.. Rheumatology (Oxford, England). https://doi.org/10.1093/rheumatology/keag577