M05.079 ICD-10-CM Code: Felty's syndrome, unspecified ankle and foot
HCC Buddy Code Card
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Inflammatory polyarthropathies (M05-M14)
M05.079
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceFelty's syndrome, unspecified ankle and foot
Felty's syndrome affecting the ankle and foot when the specific side (left or right) is not documented or specified.
Buddy Insight
Felty's syndrome with unspecified ankle and foot involvement represents the complete diagnostic triad affecting lower extremity function without documented laterality.
CMS-HCC V28
MappedHCC 93
RAF 0.175
CMS-HCC V24
MappedHCC 40
RAF 0.307
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 40
RAF 0.0
RXHCC
MappedHCC 83
RAF 0.0
Code Trumping
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Code Book Path
Inclusion Terms
Official- Felty's syndrome, tarsus, metatarsus and phalanges
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M05.079 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M05.079 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for M05.079 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M05.079 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M05.079 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for M05.079 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is M05.079 an HCC code?
Yes. M05.079 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under the CMS-HCC V28 risk adjustment model (and Rheumatoid Arthritis and Inflammatory Connective Tissue Disease 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 M05.079
For M05.079to 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 M05.079 during that encounter, not just copy-forwarded from a problem list.
What This Code Means
M05.079 is the ICD-10-CM diagnosis code for felty's syndrome, unspecified ankle and foot. Felty's syndrome affecting the ankle and foot when the specific side (left or right) is not documented or specified. M05.079 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering inflammatory polyarthropathies (m05-m14).
Under the CMS-HCC V28 risk adjustment model, M05.079 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 93) with a community, non-dual, aged base RAF weight of 0.175. Under the older V24 model, M05.079 mapped to the same category but with a base RAF weight of 0.307, 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 laterality cannot be determined from the medical record. Because M05.079 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 M05.079 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 laterality cannot be determined from the medical record
- •Query the provider if possible to determine whether the condition affects the right or left ankle/foot for more specific coding
Clinical Significance
Felty's syndrome with unspecified ankle and foot involvement represents the complete diagnostic triad affecting lower extremity function without documented laterality. This severe condition creates significant ambulatory challenges and life-threatening immunosuppression requiring comprehensive multidisciplinary care coordination and intensive monitoring protocols.
Documentation Requirements
- ✓Documentation of rheumatoid arthritis affecting ankle and foot without laterality specification
- ✓Clinical or radiologic evidence of splenomegaly
- ✓Laboratory confirmation of neutropenia with quantitative values
- ✓Ankle and foot involvement noted but side not specified
- ✓Assessment of ambulatory function and weight-bearing capacity
- ✓Evaluation of immune status and infection complications
- ✓Treatment protocol addressing all syndrome components
- ✓Podiatric consultation and mobility assistance needs evaluation
Commonly Confused Codes
- •M05.071 or M05.072: When ankle/foot laterality is actually documented in records
- •M05.9: Rheumatoid arthritis seropositive without the complete syndrome
- •M19.079: Osteoarthritis of ankle and foot unspecified without inflammatory basis
- •D70.9: Neutropenia without associated rheumatoid arthritis
- •M25.579: Pain in unspecified ankle and foot without systemic components