Advancing stiffness measurement in rheumatic disease: report from the Stiffness Special Interest group at OMERACT 2018

Objective To improve measurement of stiffness in rheumatic disease. Methods Data presented included: 1) Two qualitative projects; 2) The RA Stiffness patient-reported outcome measure (RAST); 3) three items assessing stiffness severity, duration, and interference. 3) Results Stiffness is multidimensional and includes aspects of stiffness experience such as duration, severity, and impact. Stiffness items showed construct validity in RA. Further efforts are required to develop an instrument that will be taken through OMERACT Filter 2.1 for instrument selection. Conclusion The future research agenda for the group includes domain content voting for individual diseases, and development of stiffness item banks and disease-specific short forms.