What is ICD-10 code M45.3?

M45.3 is the ICD-10-CM diagnosis code for Ankylosing spondylitis of cervicothoracic region. Ankylosing spondylitis affecting the area where the neck meets the upper back (cervicothoracic region). It belongs to the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99). M45.3 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M45.3 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. M45.3 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. M45.3 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for M45.3?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For M45.3, V28 maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders at RAF 0.617 while V24 mapped to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease at RAF 0.421. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting M45.3?

Confirm documentation indicates involvement of the cervicothoracic junction specifically Distinguish from isolated cervical or thoracic involvement by reviewing imaging and clinical notes Because M45.3 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

2026 ICD-10-CM M45.3: Ankylosing spondylitis

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Code lookupM45.3Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Spondylopathies (M45-M49)

M45.3

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Ankylosing spondylitis of cervicothoracic region

Ankylosing spondylitis affecting the area where the neck meets the upper back (cervicothoracic region).

Buddy Insight

Ankylosing spondylitis of the cervicothoracic region affects the junction between neck and mid-back, potentially causing breathing difficulties and upper extremity symptoms.

CMS-HCC V28

Mapped

HCC 93

Rheumatoid Arthritis and Othe...

RAF 0.617

CMS-HCC V24

Mapped

HCC 40

Rheumatoid Arthritis and Infl...

RAF 0.421

ACA/HHS

Mapped

HCC 56

HHS-HCC 56

Varies by metal level

ESRD/PACE

Mapped

HCC 40

Rheumatoid Arthritis and Infl...

RAF 0.058

RXHCC

Mapped

HCC 83

Rheumatoid Arthritis and Infl...

RAF 0.222

Code Book Path

Official

M45Ankylosing spondylitis

M45.3Ankylosing spondylitis of cervicothoracic region

Inclusion Terms

Official

Rheumatoid arthritis of spine

Excludes 2

Official

Behçet's disease (M35.2)

Related Child Codes

Official

M45.0Ankylosing spondylitis of multiple sites in spine

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

M45.2Ankylosing spondylitis of cervical region

M45.4Ankylosing spondylitis of thoracic region

M45.5Ankylosing spondylitis of thoracolumbar region

Includes

Official

ICD-10-CM does not list Includes notes for M45.3 in this effective period.

Excludes 1

Official

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

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M45.3 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M45.3 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M45.3 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation of ankylosing spondylitis involving cervicothoracic junction

Imaging showing inflammatory changes at cervicothoracic transition

Assessment of respiratory function and chest expansion

Evaluation for upper extremity radicular symptoms

MEAT Support

HCC Buddy guidance

Documentation of ankylosing spondylitis involving cervicothoracic junction

Imaging showing inflammatory changes at cervicothoracic transition

Assessment of respiratory function and chest expansion

Evaluation for upper extremity radicular symptoms

Audit Caution

HCC Buddy guidance

Using single-region codes when transition zone is specifically involved

Confusing with degenerative conditions of the cervicothoracic junction

Missing the unique challenges of managing transition zone involvement

Failing to assess both cervical and thoracic function impacts

Common Mistakes

HCC Buddy guidance

M45.2 — Ankylosing spondylitis of cervical region (misses thoracic component)

M45.4 — Ankylosing spondylitis of thoracic region (misses cervical component)

M47.813 — Spondylosis without myelopathy, cervicothoracic region (degenerative)

M54.13 — Radiculopathy, cervicothoracic region (nerve root symptoms only)

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is M45.3 an HCC code?

Yes. M45.3 (Ankylosing spondylitis of cervicothoracic region) maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders under the CMS-HCC V28 risk adjustment model (and Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under V24), with a community non-dual aged RAF of 0.617. It is billable for payment year 2026.

Coder answer: M45.3 is billable and maps to V28 HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: M45.3
Description: Ankylosing spondylitis of cervicothoracic region
HCC (V28): HCC 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
RAF: 0.617
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders

0.617

V24HCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.421

ESRDHCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.058

RxHCCHCC 83, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.222

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work M45.3 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for M45.3

For M45.3 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed M45.3 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

M45.3 is the ICD-10-CM diagnosis code for ankylosing spondylitis of cervicothoracic region. Ankylosing spondylitis affecting the area where the neck meets the upper back (cervicothoracic region). M45.3 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering spondylopathies (m45-m49).

Under the CMS-HCC V28 risk adjustment model, M45.3 maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders (HCC 93) with a community, non-dual, aged base RAF weight of 0.617. Under the older CMS-HCC V24 model, M45.3 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 40) with a community, non-dual, aged base RAF weight of 0.421. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Confirm documentation indicates involvement of the cervicothoracic junction specifically. Because M45.3 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for M45.3 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Confirm documentation indicates involvement of the cervicothoracic junction specifically
•Distinguish from isolated cervical or thoracic involvement by reviewing imaging and clinical notes

Clinical Significance

Ankylosing spondylitis of the cervicothoracic region affects the junction between neck and mid-back, potentially causing breathing difficulties and upper extremity symptoms. This location can significantly impact respiratory function and requires monitoring for both cervical and thoracic complications.

Documentation Requirements

✓Documentation of ankylosing spondylitis involving cervicothoracic junction
✓Imaging showing inflammatory changes at cervicothoracic transition
✓Assessment of respiratory function and chest expansion
✓Evaluation for upper extremity radicular symptoms
✓Documentation of spinal mobility restrictions in transition zone
✓Functional assessment of neck and upper back mobility
✓Treatment response specific to cervicothoracic involvement

Commonly Confused Codes

•M45.2: Ankylosing spondylitis of cervical region (misses thoracic component)
•M45.4: Ankylosing spondylitis of thoracic region (misses cervical component)
•M47.813: Spondylosis without myelopathy, cervicothoracic region (degenerative)
•M54.13: Radiculopathy, cervicothoracic region (nerve root symptoms only)
•M46.03: Spinal enthesopathy, cervicothoracic region (different inflammatory process)