BACKGROUND: Ankylosing spondylitis (AS) is a chronic immune-mediated inflammatory disease. The prevailing theory links AS onset to infections in susceptible individuals. Furthermore, infections may impair the immune responses. Numerous studies have investigated links between AS and various infections-bacterial, viral, fungal, and other microorganism infections. However, limited attention has been given to the association between AS and Clonorchis sinensis (C. sinensis) infection. CASE SUMMARY: A 27-year-old male with a 10-yr history of AS presented to our hospital with inflammatory lower back pain as the primary manifestation. Ten years ago, the patient had achieved a stable condition after treatment with biological agents. However, he experienced a recurrence of lumbosacral pain with an unexplained cause 10 d before hospital admission. A lumbosacral magnetic resonance imaging (MRI) scan revealed bone marrow edema in the left sacroiliac joint, and laboratory indicators were elevated. Moreover, the presence of C. sinensis eggs was detected in the stool. The patient was prescribed praziquantel, resulting in the disappearance of C. sinensis eggs in subsequent routine stool tests and relief from lumbosacral pain. A follow-up MRI scan performed after 4 months revealed a reduction in bone marrow edema around the left sacroiliac joint. CONCLUSION: C. sinensis infections could potentially trigger the exacerbation of AS. Clinicians should pay attention to investigating the presence of infections.
