M45Not billable, use a more specific code below

Ankylosing spondylitis

In Spondylopathies (M45-M49), chapter 13: Diseases of the Musculoskeletal System and Connective Tissue

20 billable codes under M45: none are a CC or MCC; all map to HCC 93 (Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders).An HCC counts toward a Medicare Advantage patient's risk score.

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Instructional notes

Includes: conditions that are coded here

  • Rheumatoid arthritis of spine

Excludes1: not coded here, use a different code

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

Excludes2: not included here, code separately if applicable

  • Behçet's disease (M35.2)

Official coding guidelines

From the ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027 (CMS and NCHS). Links open the PDF at the right page.

Covers site and laterality, acute injury versus chronic musculoskeletal conditions, 7th characters for pathologic fractures, osteoporosis with or without current fracture, and multisystem inflammatory syndrome.

Read Section I.C.13 (page 60)

M45 MS-DRGs

As the principal diagnosis, all 20 billable codes under M45 group to MS-DRG 545, 546, or 547 (v44.0). Which one applies depends on procedures performed, secondary diagnoses (CC/MCC), and the patient's age and discharge status.

Other codes that refer to M45

Notes on these codes point to M45.

  • G55 Excludes1: nerve root compression (due to) (in) ankylosing spondylitis (M45.-)
  • J99 Code First: ankylosing spondylitis (M45.-)
  • M05 Excludes1: rheumatoid arthritis of spine (M45.-)

About the condition

Plain-language background from MedlinePlus (National Library of Medicine), not coding guidance.

Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a type of arthritis of the spine. It causes inflammation (swelling) between your vertebrae (the bones that make up your spine) and the joints between your spine and pelvis. AS inflammation can cause stiffness and make it difficult to move and bend.

Read more about ankylosing spondylitis on MedlinePlus

Code history

Valid since FY2016, when ICD-10-CM took effect on October 1, 2015. No changes since.