Analysis of Potential Subtypes of SAPHO Syndrome

Objectives: The purpose of this study is to identify clinical subtypes of SAPHO syndrome using cluster analysis, and to systematically investigate the associated clinical characteristics, therapeutic approaches, and short-term prognostic outcomes in order to enhance patient management. Methods: We recruited patients who had been diagnosed with SAPHO syndrome at Beijing Jishuitan Hospital. Bone lesions were assessed using a ⁹⁹Tc bone scan. Based on bone lesions and clinical features, patients were categorized using a hierarchical clustering algorithm. Laboratory test results and prognostic differences were compared among clusters. Results: Overall, 135 patients were included. Cluster analysis identified three distinct clusters. Eighty-seven patients were assigned to cluster 1, characterized by anterior chest wall involvement; 74.7% also had skin involvement. Nineteen patients were assigned to cluster 2, characterized by spinal involvement, and 10.5% showed skin manifestations. Twenty-nine patients were assigned to cluster 3, characterized by peripheral bone involvement, with 24.1% exhibiting skin manifestations. Patients in cluster 3 were younger at disease onset (36.92 ± 16.62 years); their BASDAI and BASFI scores were lower (2.51 ± 1.18 and 0.89 ± 1.37, respectively). In cluster 1, significant reductions in Visual Analog Scale scores were observed at 1 and 6 months after treatment compared with baseline (7.08 vs. 2.59, p < 0.001, n = 63; 7.09 vs. 1.93, p < 0.001, n = 45). Similar improvements were noted in clusters 2 and 3 (7.18 vs. 3.00, p < 0.001, n = 11; 7.00 vs. 3.00, p < 0.001, n = 7; 6.70 vs. 2.65, p < 0.001, n = 20; 6.60 vs. 2.47, p < 0.001, n = 15). Conclusions: SAPHO syndrome may be classified into three subtypes: typical, axial, and peripheral. All subtypes show rapid improvement with timely treatment. Defining the clinical characteristics of these three subtypes can aid diagnosis and provide pathogenesis insights regarding this heterogeneous syndrome.