A66.6 ICD-10-CM Code: Bone and joint lesions of yaws
A66.6 maps to CMS-HCC V28 92. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools
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FY 2026 Apr update / Certain infectious and parasitic diseases (A00-B99) / Other spirochetal diseases (A65-A69)
A66.6
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceBone 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.
Buddy Insight
Bone and joint lesions of yaws represent late-stage tropical infection that causes destructive skeletal changes, reflecting chronic infectious disease burden.
CMS-HCC V28
MappedHCC 92
Coefficient HCC 92: 0.479 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 055
Code-level coefficient reference
ESRD/PACE
MappedHCC 39
Code-level coefficient reference
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
Official- Yaws ganglion
- Yaws goundou
- Yaws gumma, bone
- Yaws gummatous osteitis or periostitis
- Yaws hydrarthrosis
- Yaws osteitis
- Yaws periostitis (hypertrophic)
Excludes 2
Official- carrier or suspected carrier of infectious disease (Z22.-)Inherited from A00-B99, A65-A69
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)Inherited from A00-B99, A65-A69
- infectious and parasitic diseases specific to the perinatal period (P35-P39)Inherited from A00-B99, A65-A69
- influenza and other acute respiratory infections (J00-J22)Inherited from A00-B99, A65-A69
- leptospirosis (A27.-)Inherited from A00-B99, A65-A69
- syphilis (A50-A53)Inherited from A00-B99, A65-A69
Related Codes
Includes
Official- diseases generally recognized as communicable or transmissibleInherited from A00-B99, A66
- boubaInherited from A00-B99, A66
- frambesia (tropica)Inherited from A00-B99, A66
- pianInherited from A00-B99, A66
Excludes 1
Official- certain localized infections - see body system-related chaptersInherited from A00-B99
Code First
OfficialNo Code First sequencing instructions are included in this display for A66.6. Check the code and parent instructions in the Code Book.
Use Additional
Official- code to identify resistance to antimicrobial drugs (Z16.-)Inherited from A00-B99
Code Also
OfficialNo Code Also instructions are included in this display for A66.6. Check the code and parent instructions in the Code Book.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 A66.6 an HCC code?
Yes. A66.6 (Bone and joint lesions of yaws) maps to HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.479. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: A66.6 is billable and maps to V28 HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- A66.6
- Description
- Bone and joint lesions of yaws
- HCC (V28)
- HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
- RAF reference coefficient
- 0.479
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work A66.6 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for A66.6
For A66.6, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- 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
Coder workflow notes
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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/Severe Soft Tissue Infections/Necrosis (HCC 92) with a source-labeled community, non-dual, aged reference coefficient of 0.479. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
Yaws (A66) is an infectious disease primarily found in tropical and subtropical regions; verify the patient's geographic history or exposure when coding. For A66.6, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, 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