M86.331
BillableChronic multifocal osteomyelitis, right radius and ulna
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.331 an HCC code?
Yes. M86.331 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 M86.331
For M86.331 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 M86.331 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.331 is the ICD-10-CM diagnosis code for chronic multifocal osteomyelitis, right radius and ulna. A chronic bone infection affecting multiple areas of the right forearm bones (radius and ulna), characterized by persistent inflammation and bone damage. M86.331 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, M86.331 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, M86.331 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.
Verify laterality is documented as right in the medical record before assigning this code. Because M86.331 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 M86.331 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify laterality is documented as right in the medical record before assigning this code
- •Confirm the infection is multifocal (affecting multiple sites) and chronic in nature, not acute
Clinical Significance
This code represents a severe chronic bone infection specifically affecting both forearm bones of the right arm, indicating significant functional impairment and treatment complexity. The multifocal nature suggests extensive disease requiring prolonged antibiotic therapy and potential surgical intervention.
Documentation Requirements
- ✓Confirmation of right-sided radius and ulna involvement
- ✓Evidence of chronicity (>6 weeks duration or recurrent episodes)
- ✓Documentation of multifocal pattern (multiple areas within bones)
- ✓Radiographic evidence of osteomyelitic changes on imaging
- ✓Clinical symptoms (pain, swelling, decreased range of motion)
- ✓Laboratory markers (elevated inflammatory markers, culture results)
- ✓Treatment response documentation (antibiotic therapy outcomes)
- ✓Provider assessment confirming chronic multifocal osteomyelitis