Rapid radiographic progression of axial spondyloarthritis: A case of diffuse bone marrow oedema evolving to bamboo spine over 9 years.

Axial spondyloarthritis (axSpA) is a chronic inflammatory disease that primarily affects the sacroiliac joints and spine, leading to progressive structural changes. The clinical course of axSpA is heterogeneous, and cases of rapid structural progression over a relatively short period have been reported. With the advent of biologic agents, it is now possible to suppress structural damage, highlighting the importance of early diagnosis and treatment. However, reports describing the early features of rapidly progressive axSpA are limited. We report the case of a 55-year-old man who presented with low back pain following a fall. Imaging revealed a vertebral fracture at T12/L1 and a bamboo spine, and he underwent percutaneous posterior fixation. Sacroiliac joint ankylosis was also observed, and a diagnosis of ankylosing spondylitis was made. The patient had visited our hospital 9 years earlier for low back pain. At that time, magnetic resonance imaging showed diffuse bone marrow oedema across multiple vertebrae and depression of the vertebral endplates. However, the oedema was not localised to the vertebral corners, and the findings were interpreted as Schmorl's nodes with surrounding oedema. Based on the current findings, the previous imaging was retrospectively interpreted as an early sign of axSpA. This case highlights that diffuse vertebral bone marrow oedema without typical corner lesions may signal rapidly progressive axSpA. Recognition of such atypical early imaging features is critical to ensure timely diagnosis and management.