Does multi-level facet joint ankylosis without vertebral body ankylosis heighten your suspicion for axial spondyloarthritis, or can isolated facet joint ankylosis be explained by degenerative disease of the spine alone?

On x-ray or CT, if the patient is young and thin, I would certainly have a heightened suspicion for axial spondylarthritis. MRI is useful in this scenario as characteristic MRI findings of inflammation in the facet joints, such as bone marrow edema, can help distinguish from purely degenerative lesions.

Baraliakos et al., PMID 35609977

Facet joint ankylosis, particularly in the thoracic spine can precede syndesmophytes by years.

Stal et al., PMID 32417911