Ankylosing spondylitis with documented inflammatory involvement localized to the lumbar spine region, classified under the spondyloarthropathy family of conditions.
Verified May 8, 2026 · 5 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 12
- Region
- Spine
Documentation tips
What should appear in the chart to support M45.6.
Source · Editorial brief grounded in 5 cited references ↓
- Specify 'lumbar region' by name in the assessment — vague entries like 'ankylosing spondylitis' without a spinal level will force a drop to M45.9.
- Record HLA-B27 status, CRP/ESR values, and MRI or radiographic findings (sacroiliitis grade, syndesmophytes, bamboo spine appearance) to support medical necessity.
- If imaging shows involvement at multiple spinal levels, document the primary or most symptomatic region; if truly multisegmental, document that explicitly so the coder can assign M45.0 instead of M45.6.
- Note whether the patient is an adult — juvenile AS (patient under 16 at onset) routes to M08.1, not M45.6.
- For spinal cord stimulator work-ups, confirm M45.6 is listed on the claim as a supporting diagnosis per CMS LCD A57792 requirements.
Related CPT procedures
Procedure codes commonly billed with M45.6. Linking the right diagnosis to the right procedure is what establishes medical necessity.
Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis
Common coding pitfalls
The recurring mistakes coders make with M45.6 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Coding M45.6 when the record documents lumbar AND sacral involvement — that presentation maps to M45.7 (lumbosacral) or M45.8, not M45.6.
- Using the nonbillable parent M45 without a 4th character; every AS claim requires a site-specific subcategory (M45.0 through M45.9 or M45.A-series for non-radiographic axial spondyloarthritis).
- Confusing non-radiographic axial spondyloarthritis (nr-axSpA) with classical AS — nr-axSpA without radiographic sacroiliitis codes to M45.A5 (thoracolumbar) or M45.A6 (lumbar), not M45.6.
- Assigning M45.6 for juvenile patients — M08.1 is the correct code when AS onset is in a patient under 16.
- Defaulting to M45.9 (unspecified) because the provider didn't document the level; query the provider before submitting rather than guessing.
Clinical context
Source · Editorial summary grounded in 5 cited references ↓
M45.6 applies when ankylosing spondylitis (AS) affects the lumbar region specifically and documentation supports that localization. AS is a chronic seronegative inflammatory arthropathy primarily targeting the axial skeleton; the lumbar spine is among the most commonly affected segments. Use M45.6 only when the clinical record, imaging, or lab findings (sacroiliitis on MRI or plain film, HLA-B27 positivity, elevated CRP/ESR) support lumbar AS rather than multisegment involvement.
If disease spans multiple spinal regions, M45.0 (multiple sites) is the correct code — not M45.6. If the lumbar and sacral segments are both involved, consider M45.7 (lumbosacral) or M45.8 (sacral/sacrococcygeal) depending on where the primary involvement is documented. When the provider does not specify the spinal level, M45.9 (unspecified sites) applies, but that code carries audit risk and payer scrutiny — push for specificity at the point of documentation.
M45.6 is explicitly excluded from use when the patient is under 16 (juvenile ankylosing spondylitis maps to M08.1) or when the diagnosis is arthropathy in Reiter's disease (M02.3-) or Behçet's disease (M35.2). CMS recognizes M45.6 as a supporting diagnosis for spinal cord stimulator medical necessity under LCD policy.
Sibling codes
Other billable codes under M45 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 5 cited references ↓
01What is the difference between M45.6 and M45.7?
02Can M45.6 be used for a juvenile patient?
03When should I use M45.0 instead of M45.6?
04Does M45.6 support medical necessity for spinal cord stimulator placement?
05How does M45.6 differ from the non-radiographic axial spondyloarthritis codes (M45.A-series)?
06Is Behçet's disease excluded from M45.6?
07What happens if the provider documents 'ankylosing spondylitis' without specifying the spinal level?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 — code M45.6
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M45-M49/M45-/M45.6
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M45.6
- 04icdcodes.aihttps://icdcodes.ai/diagnosis/ankylosing-spondylitis/documentation
- 05cms.govhttps://www.cms.gov/medicare-coverage-database/view/article.aspx?articleId=57792&ver=12
Mira AI Scribe
Mira AI Scribe captures the specific spinal region (lumbar), relevant lab markers (HLA-B27, CRP, ESR), and imaging findings (sacroiliitis grade, syndesmophytes on MRI or plain film) from the encounter note to lock in M45.6 over the unspecified M45.9 — preventing payer downcoding, audit flags, and medical necessity denials on high-cost procedures like spinal cord stimulation.
See how Mira captures M45.6 documentation