A66.6
BillableBone and joint lesions of yaws
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is A66.6 an HCC code?
Yes. A66.6 maps to Bone/Joint/Muscle Infections/Necrosis under the CMS-HCC V28 risk adjustment model (and Bone/Joint/Muscle Infections/Necrosis 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 A66.6
For A66.6 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 A66.6 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
A66.6 is the ICD-10-CM diagnosis code for bone and joint lesions of yaws. Yaws is a tropical infection caused by bacteria that can damage bones and joints, causing pain, swelling, and deformity. This code specifically identifies when the infection has affected the skeletal system. A66.6 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering other spirochetal diseases (a65-a69).
Under the CMS-HCC V28 risk adjustment model, A66.6 maps to Bone/Joint/Muscle Infections/Necrosis (HCC 92) with a community, non-dual, aged base RAF weight of 0.209. Under the older V24 model, A66.6 mapped to the same category but with a base RAF weight of 0.482 — 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.
Yaws (A66) is an infectious disease primarily found in tropical and subtropical regions; verify the patient's geographic history or exposure when coding. Because A66.6 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 A66.6 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Yaws (A66) is an infectious disease primarily found in tropical and subtropical regions; verify the patient's geographic history or exposure when coding
- •When bone and joint lesions are documented, ensure this is the most specific code available rather than using a more general yaws code, and document which bones/joints are affected for complete medical record
Clinical Significance
Bone and joint lesions of yaws represent late-stage tropical infection that causes destructive skeletal changes, reflecting chronic infectious disease burden. While rare in the United States, this condition may be encountered in immigrant populations from endemic tropical regions and requires awareness of its distinct clinical and coding profile.
Documentation Requirements
- ✓Confirmed yaws diagnosis (caused by Treponema pallidum pertenue) with serological testing
- ✓Specific bones and/or joints affected with imaging documentation
- ✓Stage of yaws infection (typically tertiary/late for bone involvement)
- ✓Geographic or exposure history supporting the diagnosis
- ✓Treatment plan and disease activity status
Commonly Confused Codes
- •A52.77 (Syphilis of bone and joint) — Both are treponemal diseases but caused by different subspecies; yaws (T. pallidum pertenue) is transmitted by skin contact, not sexually
- •M86.9 (Osteomyelitis, unspecified) — General bone infection; yaws osteitis has specific treponemal etiology and tropical disease history
- •A66.2 (Other early skin lesions of yaws) — Early yaws affects skin only; A66.6 indicates progression to bone and joint involvement