M86.329
BillableChronic multifocal osteomyelitis, unspecified humerus
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.329 an HCC code?
Yes. M86.329 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 M86.329
For M86.329 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 M86.329 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.329 is the ICD-10-CM diagnosis code for chronic multifocal osteomyelitis, unspecified humerus. A long-standing bone infection affecting multiple bones with humerus involvement, but the specific arm (right or left) is not specified. M86.329 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering other osteopathies (m86-m90).
Under the CMS-HCC V28 risk adjustment model, M86.329 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, M86.329 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.
Use this code only when the specific humerus cannot be determined; request clarification from the provider when possible. Because M86.329 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 M86.329 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code only when the specific humerus cannot be determined; request clarification from the provider when possible.
- •Document that the humerus is involved but laterality is unspecified.
Clinical Significance
Chronic multifocal osteomyelitis represents a severe, persistent bone infection affecting multiple sites simultaneously, requiring aggressive long-term management. This condition significantly impacts patient mobility, quality of life, and carries substantial risk for complications including pathologic fractures and systemic sepsis.
Documentation Requirements
- ✓Specific anatomical location (humerus) with laterality when known
- ✓Evidence of chronicity (duration >6 weeks or recurrent episodes)
- ✓Documentation of multifocal involvement (multiple bone sites affected)
- ✓Imaging findings (X-ray, MRI, or bone scan showing osteomyelitic changes)
- ✓Laboratory evidence (elevated ESR, CRP, or positive cultures when available)
- ✓Clinical symptoms (bone pain, swelling, functional limitation)
- ✓Treatment history (antibiotic therapy, surgical interventions)
- ✓Provider assessment confirming chronic osteomyelitis diagnosis