M86.379
BillableChronic multifocal osteomyelitis, unspecified ankle and foot
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.379 an HCC code?
Yes. M86.379 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 M86.379
For M86.379 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 M86.379 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.379 is the ICD-10-CM diagnosis code for chronic multifocal osteomyelitis, unspecified ankle and foot. A chronic bone infection affecting multiple areas of the ankle and foot when the specific side (left or right) is not specified in the medical record. M86.379 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, M86.379 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, M86.379 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.
This is a default code when laterality is unspecified; attempt to clarify with provider. Because M86.379 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 M86.379 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a default code when laterality is unspecified; attempt to clarify with provider
- •Review imaging reports and clinical notes for any laterality clues
Clinical Significance
Chronic multifocal osteomyelitis of unspecified ankle and foot indicates a severe bone infection affecting weight-bearing structures without documented laterality, representing significant risk for mobility impairment. This condition requires comprehensive treatment due to the critical role of foot/ankle in ambulation.
Documentation Requirements
- ✓Documentation of ankle and foot involvement without laterality
- ✓Evidence of chronic infection (>6 weeks duration or recurrent)
- ✓Confirmation of multifocal pattern in ankle/foot bones
- ✓Imaging findings consistent with chronic osteomyelitis
- ✓Assessment of functional impact on weight-bearing
- ✓Laboratory evidence supporting chronic infectious process
- ✓Treatment documentation and response patterns
- ✓Absence of clear laterality specification in record