Correlation Between the Peak of Skin Thickness Progression Rate and Onset of Cardiopulmonary Involvement in Thai Systemic Sclerosis Patients

<b>Background/Objectives:</b> Rapid skin thickness progression assessed using the modified Rodnan skin score (mRSS) is associated with poor outcomes in systemic sclerosis (SSc). However, the correlation between patterns of skin thickness and the onset of internal organ involvement remains unclear. This study aimed to determine the correlation between peak skin thickness progression rate (pSTPR) and the onset of internal organ involvement, particularly interstitial lung disease (ILD) and pulmonary arterial hypertension (PAH) among Thai SSc patients. <b>Method:</b> A prospective cohort study with retrospective analysis was conducted on adult SSc patients who experienced the onset of their first non-Raynaud phenomenon symptoms between January 2013 and December 2020 and had at least a 2-year follow-up. Patients with an overlap syndrome were excluded from this study. The pSTPR was calculated by dividing the peak of the mRSS by the duration of disease at the peak of the mRSS. <b>Result:</b> A total of 509 patients were included in this study. The majority of cases were female (351; 69.0%) and comprised diffuse cutaneous SSc subsets (353 cases; 69.4%). The respective mean age and median pSTPR was 48.2 ± 11.6 years and 1.63 points/year (interquartile range 0.5-4.4). The respective median durations of disease at the onset of significant ILD (>20% extent), ILD, and mean duration of disease at the onset of PAH were 3.4 (Q1-Q3 1.4-7.7), 5.4 (Q1-Q3 2.4-9.2), and 8.0 ± 4.9 years. pSTPR was negatively correlated with disease duration at the onset of significant ILD (Rho -0.509, <i>p</i> < 0.001), ILD (Rho -0.480, <i>p</i> < 0.001), PAH (Rho -0.372, <i>p</i> = 0.03), and disease duration from onset to death (Rho -0.367, <i>p</i> = 0.03) after adjusting for age, sex, and anti-topoisomerase I. <b>Conclusion:</b> SSc patients with a high skin thickness progression rate reaching the maximum point of mRSS were at risk of developing early ILD, PAH, and death. The pSTPR may be used to assess individuals at risk of experiencing early onset cardiopulmonary involvement in SSc.