What is ICD-10 code M05.179?

M05.179 is the ICD-10-CM diagnosis code for Rheumatoid lung disease with rheumatoid arthritis of unspecified ankle and foot. A condition where rheumatoid arthritis affects an unspecified ankle and foot and also causes inflammation in the lungs. M05.179 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M05.179 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. M05.179 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. M05.179 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for M05.179?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For M05.179, V28 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease at RAF 0.175 while V24 mapped to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease at RAF 0.307. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting M05.179?

Use only when laterality cannot be determined from available documentation Attempt to clarify whether right or left ankle/foot is affected before using this code Because M05.179 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

M05.179 ICD-10 Code: Rheumatoid lung disease

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupM05.179Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Inflammatory polyarthropathies (M05-M14)

M05.179

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Rheumatoid lung disease with rheumatoid arthritis of unspecified ankle and foot

A condition where rheumatoid arthritis affects an unspecified ankle and foot and also causes inflammation in the lungs.

Buddy Insight

CMS-HCC V28

Mapped

HCC 93

Rheumatoid Arthritis and Infl...

RAF 0.175

CMS-HCC V24

Mapped

HCC 40

Rheumatoid Arthritis and Infl...

RAF 0.307

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 40

Rheumatoid Arthritis and Infl...

RAF 0.0

RXHCC

Mapped

HCC 83

Rheumatoid Arthritis and Infl...

RAF 0.0

Code Trumping

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Code Book Path

Official

M05.1Rheumatoid lung disease with rheumatoid arthritis

M05.17Rheumatoid lung disease with rheumatoid arthritis of ankle and foot

M05.179Rheumatoid lung disease with rheumatoid arthritis of unspecified ankle and foot

Inclusion Terms

Official

Rheumatoid lung disease with rheumatoid arthritis, tarsus, metatarsus and phalanges

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M05.179 in this effective period.

Related Child Codes

Official

M05.171Rheumatoid lung disease with rheumatoid arthritis of right ankle and foot

M05.172Rheumatoid lung disease with rheumatoid arthritis of left ankle and foot

Includes

Official

ICD-10-CM does not list Includes notes for M05.179 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M05.179 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M05.179 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M05.179 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M05.179 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Confirmed rheumatoid arthritis with appropriate laboratory findings

Documentation of ankle and foot involvement without laterality specification

Evidence of rheumatoid-related lung disease through clinical studies

Clear notation that ankle/foot laterality is unspecified or bilateral

MEAT Support

HCC Buddy guidance

Confirmed rheumatoid arthritis with appropriate laboratory findings

Documentation of ankle and foot involvement without laterality specification

Evidence of rheumatoid-related lung disease through clinical studies

Clear notation that ankle/foot laterality is unspecified or bilateral

Audit Caution

HCC Buddy guidance

Using when ankle/foot laterality is documented elsewhere in the medical record

Failing to confirm both ankle/foot RA and lung disease are present

Missing verification of rheumatoid etiology for lung pathology

Incorrectly applying when bilateral involvement should be coded separately

Common Mistakes

HCC Buddy guidance

M05.171 — Rheumatoid lung disease with RA of right ankle and foot (specific laterality)

M05.172 — Rheumatoid lung disease with RA of left ankle and foot (specific laterality)

M06.079 — Rheumatoid arthritis of unspecified ankle and foot without lung involvement

M05.169 — Rheumatoid lung disease with RA of unspecified knee (different joint)

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 M05.179 an HCC code?

Yes. M05.179 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

V28HCC 93, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.175

V24HCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.307

ESRDHCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.000

RxHCCHCC 83, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.000

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 M05.179

For M05.179to 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 M05.179 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

M05.179 is the ICD-10-CM diagnosis code for rheumatoid lung disease with rheumatoid arthritis of unspecified ankle and foot. A condition where rheumatoid arthritis affects an unspecified ankle and foot and also causes inflammation in the lungs. M05.179 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, M05.179 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, M05.179 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 only when laterality cannot be determined from available documentation. Because M05.179 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 M05.179 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Use only when laterality cannot be determined from available documentation
•Attempt to clarify whether right or left ankle/foot is affected before using this code

Clinical Significance

This code captures severe rheumatoid arthritis with ankle and foot involvement and pulmonary complications when laterality is unspecified, representing systemic disease with significant mobility and respiratory impact. The condition requires comprehensive management addressing both weight-bearing function and pulmonary monitoring.

Documentation Requirements

✓Confirmed rheumatoid arthritis with appropriate laboratory findings
✓Documentation of ankle and foot involvement without laterality specification
✓Evidence of rheumatoid-related lung disease through clinical studies
✓Clear notation that ankle/foot laterality is unspecified or bilateral
✓Clinical assessment establishing connection between RA and lung pathology
✓Mobility and gait assessment with functional limitations
✓Treatment plan addressing both ankle/foot preservation and pulmonary care

Commonly Confused Codes

•M05.171: Rheumatoid lung disease with RA of right ankle and foot (specific laterality)
•M05.172: Rheumatoid lung disease with RA of left ankle and foot (specific laterality)
•M06.079: Rheumatoid arthritis of unspecified ankle and foot without lung involvement
•M05.169: Rheumatoid lung disease with RA of unspecified knee (different joint)
•M05.10: Rheumatoid lung disease with RA of unspecified site (joint not specified)