M45.A3
BillableNon-radiographic axial spondyloarthritis of cervicothoracic region
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M45.A3 an HCC code?
Yes. M45.A3 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).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. 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.
MEAT Criteria for M45.A3
For M45.A3to 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.A3 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M45.A3 is the ICD-10-CM diagnosis code for non-radiographic axial spondyloarthritis of cervicothoracic region. An inflammatory spinal condition without radiographic bone changes affecting the cervicothoracic region (where the neck and mid-back meet). M45.A3 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.A3 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.A3 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.
Verify that imaging does not show typical ankylosing spondylitis changes before coding as non-radiographic. Because M45.A3 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.A3 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify that imaging does not show typical ankylosing spondylitis changes before coding as non-radiographic
- •Document clinical presentation and any positive inflammatory markers to support the diagnosis
Clinical Significance
Non-radiographic axial spondyloarthritis affecting the cervicothoracic junction represents involvement at the transition zone between neck and mid-back, often causing complex pain patterns. This location may require specialized physical therapy and postural interventions.
Documentation Requirements
- ✓MRI findings showing cervicothoracic inflammation
- ✓Absence of structural changes on plain radiographs
- ✓Clinical symptoms involving neck-to-shoulder region
- ✓Assessment of both cervical and thoracic mobility
- ✓Documentation of pain radiation patterns
- ✓Postural examination findings
- ✓Response to targeted anti-inflammatory therapy
- ✓Occupational or ergonomic factors
Commonly Confused Codes
- •M45.3 — Radiographic ankylosing spondylitis when bone changes present
- •M45.A2 — Cervical region when thoracic component is also involved
- •M45.A4 — Thoracic region when cervical component is also involved
- •M54.2 — Cervicalgia without thoracic involvement
- •M54.6 — Thoracic pain without cervical involvement