Is the bullhead sign on bone scintigraphy really common in the patient with SAPHO syndrome? A single-center study of a 16-year experience

OBJECTIVE: The aim of this study was to assess the bone lesion distribution and analyze the frequency of the bullhead sign in patients with SAPHO (synovitis, acne, pustulosis, hyperostosis, and osteitis) syndrome using whole-body bone scintigraphy (WBBS) in a relatively populous study population. METHODS: In this study, the Nuclear Medicine Department's records of one center were retrospectively reviewed and the patients who fulfilled the diagnostic criteria for SAPHO syndrome and underwent Tc-99m-methylene diphosphonate WBBS were identified over a 16-year period. The following data were collected from patients, including age, sex, surgically proved pathology of the bone lesions, WBBS surveillance interval, and SAPHO syndrome components. The bone lesion distribution and the frequency of bullhead sign involving the manubrium and bilateral sternoclavicular junctions were analyzed. RESULTS: Forty-eight patients were enrolled in this study. The initial WBBS indicated bone involvement in all of the 48 (100%) patients, in whom the most commonly affected region was the anterior chest wall (ACW) (100%, 48/48). The frequency of the upper costosternal junction involvement was the highest (38/48, 79.2%), and 28.9% (11/38) patients were found to show isolated involvement of the first rib in ACW. The frequency of the bullhead sign was only 22.9% (11/48, 95% CI: 12.0-37.3). In the eight (16.7%, 8/48) patients who were followed up using WBBS with an interval that ranged from 1 to 10 years, one patient with an initially single sternoclavicular junction lesion developed a typical bullhead sign over 10 years; other patients with or without the initial typical bullhead sign showed stable appearance over 1-4 years. CONCLUSION: This retrospective study shows that in patients with proposed SAPHO syndrome, the bone lesions are most likely located in ACW, and the configuration of the bullhead sign is characteristic, but not entirely sensitive. The value of upper costosternal junction involvement, especially the first rib, may be underevaluated.