Abstract
INTRODUCTION: Classification criteria aim to identify a homogenous population of patients for research. We aimed to quantify how well phase-III trials in connective tissue diseases (CTDs) represent a real-world cohort. METHODS: A comprehensive review of all major published phase-III trials in CTDs was performed (clinicaltrials.gov). Classification criteria utilised most commonly in clinical trials were applied to a multicentre unselected CTD cohort. RESULTS: There were 42 CTD trials identified, with no trials in mixed (MCTD) or undifferentiated CTD (UCTD). The majority of trials (N = 38, 90 %) required patients to meet classification criteria for their respective disease. Eight (19.0 %) excluded patients with overlapping CTDs and a further two (4.8 %) excluded specific overlapping features, such as pulmonary arterial hypertension. One study explicitly allowed overlap syndromes. Our real-world CTD cohort included 391 patients. Patients with UCTD or MCTD (91/391, 23.3 %) would be excluded from participation in clinical trials for not having an eligible diagnosis. Of patients with primary Sjögren's syndrome (pSS), SLE, systemic sclerosis (SSc) or idiopathic inflammatory myopathy (IIM), 211/300 (70.3 %) met the classification criteria for their respective diagnosis and 24/211 (11.4 %) met criteria for >1 CTD. In total, 187/391 (47.8 %) would be eligible for recruitment, based upon their physician diagnosis, and most stringent trial eligibility criteria. CONCLUSION: In an unselected, real-world CTD cohort, up to half of patients are ineligible for clinical trials due to not meeting classification criteria, overlapping features or a lack of trials within their primary disease. To address this inequality in access to novel therapies, clinical trial design should evolve eligibility criteria in CTDs.