Synovitis, acne, pustulosis, hyperostosis and osteitis （SAPHO） syndrome is a sterile, inflammatory disease of the skin and joints. It may also affect the mandible; however, it is difficult to determine whether unifocal mandible involvement is sterile or infectious in origin, often making the diagnosis difficult. We experienced a case of SAPHO syndrome with isolated involvement of the mandible that could only be diagnosed after successful diagnostic treatment. A man in his twenties who had been unsuccessfully treated for severe trismus and swelling of the left cheek and temporal region for about one month at another hospital was referred to our department for detailed examination and treatment. Lesions were found around the left mandible. Although a diagnosis of suppurative osteomyelitis was made and an antibacterial drug was administered after drainage, the symptoms improved and recurred repeatedly. Thus, we suspected a SAPHO syndrome lesion based on the clinical course. After consultation with the internal medicine physician, the symptoms were remarkably ameliorated by administering prednisolone as a diagnostic treatment. The patient has been continuing to receive a combination of drugs with no recurrence of symptoms for two years.
