Malignancies with spine infiltration, such as B cell lymphoma or acute lymphocytic leukemia, can also masquerade as axSpA, Dr. Gensler said.
Other mimics to watch out for include diffuse idiopathic skeletal hyperostosis (DISH); Scheurmann’s disease, involving an abnormal and excessive curvature of the spine; and Bertolotti syndrome, involving an extra bone between the last lumbar bone and the sacrum, Dr. Gensler said. Clinicians should also be aware of the possibility of sacral insufficiency fractures, spinal fractures and infections.
Dr. Gensler said clinicians should keep a list of pointers in mind so as not to fall into the axSpA trap. First, inflammatory back pain does not necessarily equal axSpA, even when other suggestive features are present; clinical context and concordant imaging are needed. Second, clinicians should read MRIs “like a detective,” on the lookout for other diagnoses. Third, a stress reaction and cortical irregularity don’t necessarily add up to the presence of sacroiliitis. Fourth, clinicians should have a list of diagnoses they “can’t miss,” including infections, malignancies and fractures.
Lastly, she said, it’s important to keep in mind that Hickam’s dictum—that “patients can have as many diseases as they damn well please”—often supersedes Occam’s razor, the idea that the simplest explanation is usually the best.
“The law of simplicity to explain everything,” Dr. Gensler said, “doesn’t always work.”
Thomas R. Collins is a freelance medical writer based in Florida.
References
- Maksymowych WP, van der Heijde D, Caplan L, et al. The Assessments in Spondyloarthritis International Society (ASAS) and Spondyloarthritis Research and Treatment Network (SPARTAN) Revised Classification Criteria for Axial Spondyloarthritis: Development and validation in the classification of axial SpA inception cohort study [abstract 0854]. Arthritis Rheumatol. 2025;77(suppl 9).
- Weiss PF, Brandon TG, Aggarwal A, et al. Classification criteria for axial disease in youth with juvenile spondyloarthritis. Arthritis Rheumatol. 2024 Dec;76(12):1797–1808.
- Children’s Hospital of Philadelphia. Axial Juvenile [PF3] Spondyloarthritis (AxJSpA) Classification Criteria Calculator. https://redcap.chop.edu/surveys/?s=D3CXKYTRL4M87XM8. Accessed October 31, 2025.
- Gensler LS, Ward MM, Reveille JD, et al. Clinical, radiographic and functional differences between juvenile-onset and adult-onset ankylosing spondylitis: results from the PSOAS cohort. Ann Rheum Dis. 2008 Feb;67(2):233–237.
