The incidence and mortality of connective tissue diseases: a population-level cohort study in England from 2012 to 2023.

OBJECTIVES The reported incidence and mortality of connective tissue diseases (CTDs) in England has been inconsistent in the literature. Our objective was to describe current trends in the incidence and mortality of systemic lupus erythematous (SLE), Sjögren's disease (SjD), systemic sclerosis (SSc), idiopathic inflammatory myopathies (IIM) and mixed connective tissue disease (MCTD). METHODS We conducted a retrospective population-level study using primary care records in England via the Clinical Practice Research Datalink. We included individuals ≥18 years old with new CTD diagnoses between 2012 and 2023. Our outcomes were incidence and all-cause mortality, which included age-standardised mortality rates (ASMRs), standardised mortality ratios and hazards over time using flexible parametric models. RESULTS There were a total of 22 829 incident CTD diagnoses (81.1% female, median age 57). The age and sex-standardised incidence of SLE and SSc fell over the study period 2012-2023 (SLE: 4.32-3.29 per 100 000 person years (py) and SSc: 2.33-1.86 per 100 000 py), whereas SjD and MCTD incidence remained relatively stable. In contrast, IIM diagnoses rose from 3.23-4.31 per 100 000 py. ASMRs across the study period were highest for IIM (27.83 per 1,000 py), followed by SSc (24.43), SLE (16.74), MCTD (16.27) and lowest for SjD (9.70). CONCLUSION Our findings indicated a fall in the incidence of SLE, a simultaneous rise in IIM incidence, and high all-cause mortality within IIM and SSc cohorts. Our study acknowledges the changing landscape of CTDs in England and will aid healthcare resource planning for this vulnerable population.