Patient-reported outcome instruments in clinical trials of systemic sclerosis

Patient-reported outcome instruments provide valuable insight into disease-related morbidity known only to the patient and complement more objective outcome tools in the clinical trial setting. They are of particular importance in systemic sclerosis owing to the challenges around defining disease activity, the episodic nature of many disease-specific manifestations and the paucity of validated objective surrogate outcome measures for use in clinical trials. Early clinical trials of systemic sclerosis often incorporated legacy patient-reported outcome instruments, but the last 20 years has witnessed the emergence of several scleroderma-specific instruments that are now being routinely used alongside other outcomes in systemic sclerosis clinical trials. More recently, the value of patient-reported outcomes has been highlighted by their prominence in the American College of Rheumatology Combined Response Index for Systemic Sclerosis that has been utilized as the primary endpoint of recent clinical trials of early diffuse systemic sclerosis. This review considers the role and performance of the various patient-reported outcome instruments utilized in systemic sclerosis clinical trials, the current positioning of patient-reported outcome instruments within clinical trial endpoint models across the range of systemic sclerosis disease manifestations and, where applicable, we shall highlight areas for future research.