Comparison of clinical and pathological features between patients of SAPHO syndrome with different microbiological findings in bone biopsy.

Objectives: To elucidate the existence of bacteria in situ and its influence on the clinical and pathological features of synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome.

Methods: A total of 34 patients diagnosed with SAPHO syndrome were allocated to two groups (bacterial positive and bacterial negative) based on next-generation sequencing (NGS) and microbiological culture through CT guided percutaneous puncture. The clinical characteristics, biochemical markers, imaging data, and pathological results of the patients were analysed and compared between the two groups. And 32 infectious suppurative osteomyelitis patients were also included in this study to compare the pathological results with SAPHO syndrome patients.

Results: The positive rate of bacteria by NGS and bacterial culture were 41.2%, respectively. And the two methods detected a wide variety of bacterial species, including cocci, bacilli, and others. The difference of clinical symptoms (such as pain, swelling, and warmth), biochemical markers, imaging findings and pathological findings were not statistically significant between the bacteria positive and the bacteria negative groups. Moreover, patients with SAPHO syndrome had less inflammatory cell infiltration and increased granulation tissue formation compared with infectious suppurative osteomyelitis patients.

Conclusions: NGS and bacterial culture expand the variety of detectable bacteria and improve the detection rate of bacteria in SAPHO syndrome. The bacteria in SAPHO patients may be low-virulence colonising bacteria presented in the skin or in the body. The less inflammatory cell infiltration in tissue may reflect a damaged ability to clear low-virulence bacteria in patients with SAPHO syndrome. The presence of low-virulence bacteria may provide a new therapy choice for refractory SAPHO patients.