Ankylosing spondylitis

Ankylosing spondylitis involving two or more distinct regions of the spine simultaneously, captured as a single billable diagnosis.

Ankylosing spondylitis localized to the uppermost spinal articulations — the occiput-C1 (atlas) and C1-C2 (axis) joints — where chronic inflammatory fusion can cause severe upper cervical instability and neurologic risk.

M45.2 identifies ankylosing spondylitis localized to the cervical spine (C1–C7), distinguishing cervical-region involvement from adjacent segments coded separately under M45.1 (occipito-atlanto-axial) or M45.3 (cervicothoracic).

Ankylosing spondylitis localized to the cervicothoracic junction, the transitional zone between the cervical and thoracic spine (roughly C7–T1).

Ankylosing spondylitis localized to the thoracic (mid-back) vertebral region, classified under the spondyloarthritis spectrum as a chronic inflammatory axial joint disease.

Ankylosing spondylitis localized to the thoracolumbar junction — the transitional zone where the thoracic spine meets the lumbar spine (approximately T12–L1) — characterized by chronic inflammatory involvement, progressive ossification, and potential fusion at that spinal segment.

Ankylosing spondylitis with documented inflammatory involvement localized to the lumbar spine region, classified under the spondyloarthropathy family of conditions.

Ankylosing spondylitis localized to the lumbosacral region of the spine, capturing inflammatory involvement at the junction of the lumbar vertebrae and sacrum.

Ankylosing spondylitis localized to the sacral and sacrococcygeal region — the lowest segment of the spine where the sacrum articulates with the coccyx.

Ankylosing spondylitis diagnosed without documentation of a specific spinal region; use only when the affected spinal site cannot be determined from available records.