From misdiagnosis to definitive diagnosis of SAPHO syndrome during a routine health check-up: a case report and literature review.

Background: SAPHO syndrome is a rare chronic autoinflammatory disease with heterogeneous clinical manifestations. Because there are no specific diagnostic biomarkers, the condition is often diagnosed late or misdiagnosed. Case presentation: A 51-year-old man presented with unexplained chest pain and low back pain. He had been evaluated at several hospitals and had received different diagnoses related to bone disease. During a routine health check-up, imaging revealed multiple osteolytic lesions in the sternum, together with sclerosis and hyperostosis involving the sternoclavicular and sternocostal joints. Laboratory testing showed elevated high-sensitivity C-reactive protein and abnormal rheumatological and immunological indices, suggesting an inflammatory disorder. After admission to the rheumatology department, bone scintigraphy demonstrated the typical "bull's head sign," providing supportive imaging evidence. Review of the external bone biopsy report, together with physical examination, laboratory testing, and imaging findings, allowed exclusion of infection, malignancy, and other spondyloarthritides. A definitive diagnosis of SAPHO syndrome was established. The patient was treated with methotrexate, non-steroidal anti-inflammatory drugs and tumor necrosis factor inhibitors, with subsequent pain relief, normalization of inflammatory markers, and stable disease during follow-up. Conclusion: Because of its non-specific and variable presentation, SAPHO syndrome is frequently misdiagnosed as malignancy, tuberculosis, spondylitis, psoriasis or other conditions. Awareness of the combination of bone and skin manifestations may reduce diagnostic delay. In appropriate clinical settings, bone scintigraphy can provide valuable supportive evidence, but diagnosis should rely on integrated clinical, imaging, and exclusionary assessment. Increased awareness and standardized evaluation may help shorten the diagnostic interval, reduce misdiagnosis and mistreatment, and improve prognosis.