Factors associated with variations in the 6-minute walk distance during the follow-up of patients with systemic sclerosis.

Introduction: The 6-minute walk distance (6MWD) is commonly used to assess functional capacity in patients with systemic sclerosis (SSc), but its ability to reflect changes in cardiopulmonary status during follow-up remains uncertain. This study aimed to investigate whether variations in the 6MWD accurately mirror changes in organ involvement over time in SSc patients.

Methods: We conducted a longitudinal study on a global cohort of 227 consecutive SSc patients, including a subgroup of 88 patients with ILD or PH, over a two-year follow-up period. Statistical analyses were performed to assess associations between variations (Δ) of 6MWD (Δ6MWD) and evolution of organ involvement.

Results: The 6MWD varied only mildly during follow-up (mean Δ6MWD - 11.6 ± 67.5 m), including in patients with ILD or PH (mean Δ6MWD - 16 ± 74 m). Significant associations were noted between Δ6MWD and variations of several SSc parameters, mostly with modifications in functional status (changes in ΔBorg (ΔΔBorg) score, p = 0.002; ΔNYHA, p < 10^- 3), PH parameters (Δright atrial area, p = 0.045; persistently elevated Nt-pro-BNP levels, p < 10^- 3), chronotropic function (ΔΔheart rate, p = 0.015; Δinitial heart rate, p = 0.024), musculoskeletal involvement (occurrence of joint symptoms, p = 0.006) and perceived quality of life (ΔHAQ-DI score, p = 0.023). In most cases, the strength of these associations was mild to moderate (R² = 0.53, adjusted R² = 0.36 in multivariate analysis), suggesting the influence of additional factors to explain the majority of Δ6MWD.

Conclusion: While it remains valuable as a marker of disability and functioning, the variation in the 6MWD does not seem to be a robust surrogate for modifications in organ involvements of SSc patients.