Cluster analysis of clinical phenotypes and its implication in 164 patients with Synovitis-Acne-Pustulosis-Hyperostosis-Osteitis syndrome / 中华风湿病学杂志

ABSTRACT

Objective To use cluster analysis to explore the clinical phenotypes of Synovitis-Acne-Pustulosis-Hyperostosis-Osteitis (SAPHO) syndrome.Methods One hundred and sixty-four patients fulfilled the Kahn and Khan's criteria for SAPHO syndrome were recruited in Peking Union Medical College Hospital from 2004 to 2015.For all patients,demographics,clinical,laboratory and imaging data were collected.Cluster analysis was performed using an iterative partitioning K-means method including 11 variables that was most characteristic in patients with SAPHO syndrome.The optimal number of clusters was determined by the elbow method and Silhouettes coefficient in combination with clinical significance.Results An optimal of two phenotypes with distinct clinical features were identified.Cluster 1 was characterized by axial skeletal involvement with older age at onset [(38±11) years] and lower prevalence of severe acne (11.2％);Cluster 2 had no axial involvement with younger age at onset [(33±8) years;U=1 800,P=0.010] and higher prevalence of severe acne (26.8％;x2=4.567,P=0.033).Cluster l patients had been treated more aggressively by baseline compared with Cluster 2 patients;and were more frequently prescribed TNF-α inhibitors (32.8％ vs 2.4％;x2=1 672.5,P＜0.01) and bisphosphonates (39.7％ vs 19.5％;x2=1962,P=0.032).Nonetheless,the disease activity indices were significantly higher at baseline in Cluster 1 than Cluster 2 patients [Bath ankylosing spondylitis disease activity index (BASDAI) (3.5±1.8) vs (2.8±2.0);U=1 800,P=0.010] [Bath ankylosing spondylitis functional Index(BASDFI) (2.4±2.3) vs (1.5±1.7);U=1 791,P=0.009).Moreover,Cluster 1 patients had significantly increased inflammatory markers at baseline compared with Cluster 2 patients [erythrocyte sedi-ment-ation rate(ESR) (34.9±2.9) mm/1 h vs (19.0±14.6) mm/1 h;U=1 204.5,P＜0.01] [high-sensitivity C-reactive protein (hs-CRP) (16±19) mg/L vs (8±11) mg/L;U=1 628,P=0.01].Conclusion Char-acterized by the presence or absence of axial skeletal involvement,two disease subtypes exist in SAPHO syndrome,which exhibit distinct features in age at onset,the prevalence of severe acne,and disease severity.