Lack of specificity of the 6-minute walk test as an outcome measure for patients with systemic sclerosis

Abstract

Objective: The 6-minute walk test (6MWT) is an important prognostic tool in various cardiovascular diseases and has been considered as a surrogate endpoint. However, conflicting results have been reported in systemic sclerosis (SSc). Our objective was to evaluate the relationships of the 6-min walking distance (6MWD) and organ damage in SSc.

Methods: Eighty-seven consecutive patients with SSc were included and prospectively investigated; they underwent 6MWT in addition to conventional assessment of possible lung, heart, kidney, skin, and muscle involvement, and disease activity scoring, severity, and quality of life determination.

Results: Twenty-six patients (30%) had an abnormal 6MWT and the mean 6MWD was 461.8 +/- 103.0 m. When considering 6MWT as a binary variable - normal or abnormal - C-reactive protein (CRP) was the only independent variable associated with abnormal 6MWT. Considered as a continuous variable, the 6MWD was associated with measures of lung involvement and inflammation, with the activity and severity of disease, and also with quality of life; nevertheless, calcinosis was the only independent factor associated in multivariate analyses with a trend for an association for CRP.

Conclusion: The 6MWD relates to broad factors in SSc and these results raise doubts about the specificity of the 6MWD in this systemic disease, and its relevance to monitoring therapy.