Exploratory clinical subgroup clustering in systemic sclerosis Results from the Indian Progressive Systemic Sclerosis Registry

Objective: To conduct an exploratory cluster analysis of systemic sclerosis patients from the baseline data of the Indian systemic sclerosis registry. Methods: Patients satisfying American College of Rheumatology-European League Against Rheumatism classification criteria for systemic sclerosis were included. The clusters formed using clinical and immunological parameters were compared. Results: Of the 564 systemic sclerosis registry participants, 404 patients were included. We derived four clusters of which three were anti-topoisomerase I predominant and one was anti-centromere antibody 2 dominant. Cluster 1 (n-82 (20.3%)) had diffuse cutaneous systemic sclerosis patients with the most severe skin disease, anti-topoisomerase I positivity, males, younger age of onset and high prevalence of musculoskeletal, vasculopathic and gastrointestinal features. Cluster 2 (n-141 (34.9%)) was also diffuse cutaneous systemic sclerosis and anti-topoisomerase I predominant but with less severe skin phenotype than cluster 1 and a lesser prevalence of musculoskeletal, vasculopathic and gastrointestinal features. Cluster 3 (n-119 (29.5%)) had limited cutaneous systemic sclerosis patients with anti-topoisomerase I positivity along with other antibodies. The proximal muscle weakness was higher and digital pitting scars were lower, while other organ involvement was similar between clusters 2 and 3. Cluster 4 (n-62 (15.30%)) was the least severe group with limited cutaneous systemic sclerosis and anti-centromere antibody predominance. Age of onset was higher with low musculoskeletal disease and a higher presence of upper gastrointestinal features. The prevalence of interstitial lung disease was similar in the three anti-topoisomerase I predominant clusters. Conclusion: With exploratory cluster analysis, we confirmed the possibility of subclassification of systemic sclerosis along a spectrum based on clinical and immunological characteristics. We also corroborated the presence of antitopoisomerase I in limited cutaneous systemic sclerosis and the association of interstitial lung disease with antitopoisomerase I.