A recent Rheumatology digest,
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Study Type: Retrospective analysis of routinely collected healthcare data

Key Question: How do referral pathways and duration of rheumatology care for MSK complaints vary across five European healthcare systems?

Key Findings:

• Primary care MSK burden was consistent across countries (25–30% of residents consulting annually), but referral rates to rheumatology varied markedly (5–38%)
• 46–70% of referred patients were discharged within 3 months; only 13–43% entered long-term rheumatology follow-up
• The UK and Sweden, despite lower referral rates and fewer rheumatologists per capita, maintained higher rates of long-term rheumatology care, attributed to selective triaging systems

Clinical Relevance: This confirms that the NHS selective triaging model concentrates rheumatology resource on complex cases, which is relevant when interpreting international benchmarking data or developing cross-national diagnostic tools applicable to UK practice.

Limitations: UK primary care consultation rates were unavailable, limiting direct comparison of the full care pathway for the NHS cohort.

Study Type: Retrospective cohort study using linked nationwide registry data

Key Question: Are there distinct patterns of healthcare use in the years preceding an RA diagnosis, and when do these deviate from the general population?

Key Findings:

• Five pre-diagnosis care trajectories identified in 6,824 seropositive RA patients: Healthy (60%), High sick leave (18%), Chronic pain (10%), High infection (9%), and High burden (3%)
• Divergence from matched population controls emerged up to 10 years before diagnosis in some groups, with earlier deviation in trajectories characterised by pain and multimorbidity
• The "Chronic pain" and "High burden" groups showed the earliest and most sustained healthcare divergence, suggesting distinct aetiological or prodromal pathways

Clinical Relevance: These findings support earlier case identification strategies within primary care and could inform risk-stratification tools relevant to NHS early arthritis pathways and RA prevention initiatives.

Limitations: The study includes only seropositive RA, limiting generalisability to seronegative disease, which represents a substantial clinical subgroup.

Study Type: Retrospective post hoc analysis of a phase 3 RCT (COAST-X)

Key Question: Do the newer 2021 data-driven MRI-SIJ definitions (PD) better identify nr-axSpA patients for clinical trials compared to the established 2009 ASAS definition (ED)?

Key Findings:

• Baseline demographics and disease characteristics were comparable across all subgroups defined by either ED or PD MRI-SIJ positivity
• Clinical response rates at week 16 (ASAS40, BASDAI50, ASDAS outcomes) were similar whether patients were classified by ED or PD criteria
• Subgroups meeting only one definition (ED but not PD, or vice versa) showed marginally lower response rates than those meeting either definition outright

Clinical Relevance: For UK rheumatologists enrolling patients in nr-axSpA trials, these findings suggest no meaningful advantage in switching to newer MRI classification criteria; the established ASAS ED remains fit for purpose in trial eligibility decisions.

Limitations: Post hoc analysis limits causal inference, and findings may not generalise beyond the ixekizumab trial population.

Study Type: Prospective cohort study with in vitro mechanistic component

Key Question: Does plasma microbial tDR-1 concentration predict progression to clinical RA in anti-CCP3-positive at-risk individuals, and what is its mechanism of action?

Key Findings:

• Baseline tDR-1 was 5.4-fold higher in non-converters vs converters (n=60 CCP3+ individuals; P=5.1×10⁻⁴), remaining significant after adjustment for shared epitope, smoking, and rheumatoid factor
• Adding tDR-1 to established risk factors improved discriminatory ability from AUROC 0.722 to 0.902 (P=0.003)
• In vitro, tDR-1 significantly downregulated type 1 interferon response genes in THP-1 macrophages, suggesting a plausible immunomodulatory mechanism

Clinical Relevance: tDR-1 could strengthen risk stratification in CCP-positive at-risk individuals, a population increasingly targeted by prevention trials (e.g., PRAIRI, APIPPRA), potentially refining who is offered preventive intervention.

Limitations: Small sample (n=60), single-centre, and relatively short follow-up in converters limits generalisability.

Study Type: Longitudinal cohort study with mechanistic laboratory sub-study

Key Question: Does IgM AAPA serve as a precursor autoantibody marking the initial breach of immune tolerance preceding other AMPAs in RA?

Key Findings:

• Pre-disease AAPA IgM positivity (27.3%) exceeded ACPA IgM positivity (11.7%), but ACPA IgM rose sharply to 51.2% approaching disease onset while AAPA IgM remained stable
• AMPAs developed in individuals who were AAPA IgM-negative at baseline, arguing against a universal AAPA-first pathway
• Germline-encoded B-cell receptors were identified in both AAPA- and ACPA-expressing B cells, suggesting ACPA responses can arise independently rather than through AAPA IgM class-switching

Clinical Relevance: Challenges the hypothesis of a single autoantibody origin in RA, with implications for early biomarker strategies and understanding pre-clinical disease in at-risk populations.

Limitations: Pre-disease cohort size was modest, limiting statistical power to detect temporal associations between AMPA subtypes.

Study Type: Comparative transcriptional profiling study (single-cell RNA sequencing of fixed lung tissue)

Key Question: What are the distinct cellular and molecular signatures of macrophage and fibroblast subpopulations in RA-ILD versus RA pulmonary nodules, and how do these compare to IPF?

Key Findings:

• RA-ILD fibroblasts showed preferential upregulation of immunoregulatory, angioregulatory, and matrix assembly pathways, whereas RA nodule macrophages predominantly upregulated innate and adaptive immune pathways — indicating only partial transcriptional overlap between the two RA lung phenotypes
• Profibrotic gene expression was significantly shared between RA-ILD and IPF across both macrophage and fibroblast populations, suggesting convergent fibrotic mechanisms
• FLEX scRNA-seq of fixed tissue produced clustering patterns consistent with conventional fresh-tissue sequencing, validating the methodology for archival specimens

Clinical Relevance: Divergent molecular pathways in RA lung disease subtypes may explain differential treatment responses and could inform future targeted therapeutic strategies for RA-ILD in UK practice.

Limitations: Small sample sizes, particularly for RA nodules (n=3), limit generalisability.

Study Type: Translational experimental study (in vitro human cell work, murine model, and human biopsy validation)

Key Question: Does aberrant IgG glycosylation in lupus nephritis drive podocyte injury via CLEC7A–SYK signalling?

Key Findings:

• LN-IgG (but not healthy or non-nephritis SLE IgG) induced CLEC7A upregulation, actin cytoskeleton disruption, reduced nephrin expression, impaired motility, and increased calcium flux in human podocytes
• Deglycosylation of LN-IgG abolished CLEC7A binding and preserved podocyte function, confirming glycan-dependence
• Pharmacological SYK inhibition and CLEC7A silencing each prevented podocyte injury; elevated CLEC7A and SYK expression was confirmed in MRL/lpr mouse kidneys and active LN human biopsies

Clinical Relevance: SYK inhibitors (e.g., fostamatinib) are already in clinical use; this identifies a mechanistic rationale for targeting the CLEC7A–SYK axis specifically in lupus nephritis, potentially informing future trial design in NHS renal lupus clinics.

Limitations: Mechanistic findings rely on in vitro and murine models; direct quantitative data from human biopsy cohorts are limited, and clinical translation remains unproven.

Study Type: Cohort study (single-centre, cross-sectional diagnostic evaluation)

Key Question: What is the diagnostic utility of IFN signature, CXCL10 levels, and antiviral activity in characterising patients with suspected type I interferonopathies?

Key Findings:

• Genetic diagnosis confirmed in 80% (37/46); IFN signature positive in 91% (31/34) of evaluable patients, with significantly higher median IFN scores versus controls (p<0.0001)
• Serum CXCL10 was elevated in patients and correlated with IFN scores (rs=0.50, p=0.003), with both markers showing strong discriminative capacity
• A distinct "undifferentiated interferonopathy" subgroup was identified with consistent clinical features and positive IFN signatures but no confirmed genetic diagnosis

Clinical Relevance: As interferonopathies increasingly enter rheumatology practice, this supports incorporating CXCL10 and IFN scoring into diagnostic pathways — tools potentially accessible within NHS specialist immunology-rheumatology services.

Limitations: Small sample size (n=46) with antiviral assays performed in only five patients limits generalisability of functional findings.