Assessment of clinical and radiological characteristics of Japanese patients with synovitis, acne, pustulosis, hyperostosis, and osteitis syndrome

Objective: This study aimed to analyse the radiological characteristics and clinical diversity of Japanese patients with synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome, a heterogeneous disorder. Methods: Radiographs and clinical information from 115 Japanese patients (female/male: 81/34; mean age at onset: 48.7 years) diagnosed with SAPHO syndrome between January 2007 and December 2020 were retrospectively reviewed. Additionally, the treatment for SAPHO syndrome was explored. Results: Among the 115 patients, 70 patients had complications, including palmoplantar pustulosis, acne, or psoriasis. Imaging studies included bone scintigraphy, magnetic resonance imaging, computed tomography, and positron emission tomography in 71, 58, 70, and 23 patients, respectively. The most frequent lesions were arthritis and hyperostosis of the sternoclavicular joints in 96 patients; spinal lesions, including sacroiliac arthritis, were observed in 85 patients. Peripheral aseptic osteitis was observed in 22 patients, and the tibia was involved in 12. The treatments consisted of analgesics, bisphosphonates, conventional synthetic disease-modifying antirheumatic drugs, and biologics (tumour necrosis factor inhibitors and interleukin-23p19 inhibitors) in 85, 15, 23, and 10 patients (8 and 2 patients), respectively. Conclusions: Sternoclavicular hyperostosis and pustulosis are frequently observed in patients with SAPHO syndrome. Biological agents were more frequently used in patients with peripheral osteitis and arthritis.