M45.3
BillableAnkylosing spondylitis of cervicothoracic region
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M45.3 an HCC code?
Yes. M45.3 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease 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 M45.3
For M45.3to 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.
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 Inflammatory Connective Tissue Disease (HCC 93) with a community, non-dual, aged base RAF weight of 0.175. Under the older V24 model, M45.3 mapped to the same category but with a base RAF weight of 0.307 — V28 recalibrated weights across the entire model. 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)