Value of the 6 min walk test in detecting cardiopulmonary involvement in patients with systemic sclerosis

Objectives: Cardiopulmonary involvement (CPI) is a major cause of morbidity and mortality in systemic sclerosis (SSc). The 6 min walk test (6MWT) is widely used to assess functional capacity, but its ability to detect incident CPI remains uncertain. This study aimed to evaluate the determinants and trajectory of 6MWT parameters over time and its diagnostic utility in identifying incident CPI in SSc.

Methods: Two large prospective SSc cohorts were analysed. Multivariable regression identified factors associated with baseline 6MWT parameters. Longitudinal changes were assessed using linear mixed models, and diagnostic accuracy for incident CPI was evaluated using predefined thresholds for a decline in 6 min walking distance (6MWD) (≥33 m) and oxygen desaturation (<95%).

Results: Patients with CPI walked 89 m less than those without (95% CI -116 to 61) and exercise-induced desaturation was more frequent in CPI (OR 17.0, 95% CI 8.7 to 33). Over time, 6MWD increased slightly by 3.0 m per year (95% CI 1.7 to 4.3). Linear mixed model analysis showed an independent association of 6MWD (-33 m, 95% CI -45 to 21) and occurrence of exercise-induced desaturation (OR 15, 95% CI 8.5 to 30) in patients with CPI. A ≥33 m decline in 6MWD had 34.7% sensitivity and 79% specificity for detecting incident CPI, while new desaturation had 10.6% sensitivity and 92.6% specificity.

Conclusion: 6MWT parameters are associated with CPI in SSc. A stable 6MWD and absence of desaturation may help rule out CPI, but their low sensitivity suggests that 6MWT alone is insufficient for screening and should be complemented by additional diagnostic modalities.