M45.1 Ankylosing spondylitis of occipito-atlanto-axial region

Billable ICD-10-CM code, FY2026.

Applies from M45 Ankylosing spondylitis

Applicable to

• Rheumatoid arthritis of spine

Excludes1 (never code together)

• arthropathy in Reiter's disease (M02.3-)
• juvenile (ankylosing) spondylitis (M08.1)

Excludes2 (not included here)

• Behçet's disease (M35.2)

Risk adjustment (HCC)

• CMS-HCC V28: HCC 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
• CMS-HCC V22: HCC 40 — Rheumatoid Arthritis and Inflammatory Connective Tissue Disease
• RxHCC V08: HCC 83 — Rheumatoid Arthritis and Other Inflammatory Polyarthropathy
• ESRD V24: HCC 40

MS-DRG index

Defines the logic of DRG(s) 545-547 in MDC 08.

Approximate ICD-9-CM (GEMs)

• 720.0 Ankylosing spondylitis (approximate)

Code annotations containing back-references to M45.1

Back-references to M45

• Type 1 Excludes: G55 Nerve root and plexus compressions in diseases classified elsewhere ("nerve root compression (due to) (in) ankylosing spondylitis (M45.-)")
• Code First: J99 Respiratory disorders in diseases classified elsewhere ("ankylosing spondylitis (M45.-)")
• Type 1 Excludes: M05 Rheumatoid arthritis with rheumatoid factor ("rheumatoid arthritis of spine (M45.-)")

Diagnosis Index entries for M45.1

• Spondylitis (chronic) › ankylosing (chronic) › occipito-atlanto-axial region

Nearby codes

• M45 Ankylosing spondylitis
• M45.0 Ankylosing spondylitis of multiple sites in spine
• M45.1 Ankylosing spondylitis of occipito-atlanto-axial region (this code)
• M45.2 Ankylosing spondylitis of cervical region
• M45.3 Ankylosing spondylitis of cervicothoracic region
• M45.4 Ankylosing spondylitis of thoracic region
• M45.5 Ankylosing spondylitis of thoracolumbar region
• M45.6 Ankylosing spondylitis lumbar region