Reliability and responsiveness of the D12 and validity of its scores as a measure of dyspnoea severity in patients with rheumatoid arthritis-related interstitial lung disease.

D12 scores possess acceptable measurement properties in RA-ILD, such that it can be used with confidence in this population to assess dyspnoea severity defined by its physical and affective components. As validation is an ongoing process, and never accomplished in a single study, additional research on the psychometric properties of the D12 in RA-ILD is encouraged.