M05.40 ICD-10-CM Code: Rheumatoid myopathy with rheumatoid arthritis of unspecified site
M05.40 maps to CMS-HCC V28 93. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Inflammatory polyarthropathies (M05-M14)
M05.40
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceRheumatoid myopathy with rheumatoid arthritis of unspecified site
Muscle weakness and inflammation (myopathy) caused by rheumatoid arthritis when the specific joint location is not identified.
Buddy Insight
This diagnosis represents rheumatoid arthritis complicated by muscle weakness and inflammation (myopathy) when the specific joint site is not documented.
CMS-HCC V28
MappedHCC 93
Coefficient HCC 93: 0.617 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 056
Code-level coefficient reference
ESRD/PACE
MappedHCC 40
Code-level coefficient reference
RXHCC
MappedHCC 83
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for M05.40. Check the code and parent instructions in the Code Book.
Excludes 2
Official- arthropathic psoriasis (L40.5-)Inherited from M00-M99
- certain conditions originating in the perinatal period (P04-P96)Inherited from M00-M99
- certain infectious and parasitic diseases (A00-B99)Inherited from M00-M99
- compartment syndrome (traumatic) (T79.A-)Inherited from M00-M99
- complications of pregnancy, childbirth and the puerperium (O00-O9A)Inherited from M00-M99
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)Inherited from M00-M99
- endocrine, nutritional and metabolic diseases (E00-E88)Inherited from M00-M99
- injury, poisoning and certain other consequences of external causes (S00-T88)Inherited from M00-M99
- neoplasms (C00-D49)Inherited from M00-M99
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)Inherited from M00-M99
Related Codes
Includes
OfficialNo Includes notes are included in this display for M05.40. Check the code and parent instructions in the Code Book.
Excludes 1
Official- rheumatic fever (I00)Inherited from M05
- juvenile rheumatoid arthritis (M08.-)Inherited from M05
- rheumatoid arthritis of spine (M45.-)Inherited from M05
Code First
OfficialNo Code First sequencing instructions are included in this display for M05.40. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for M05.40. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for M05.40. Check the code and parent instructions in the Code Book.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is M05.40 an HCC code?
Yes. M05.40 (Rheumatoid myopathy with rheumatoid arthritis of unspecified site) maps to HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.617. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: M05.40 is billable and maps to V28 HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- M05.40
- Description
- Rheumatoid myopathy with rheumatoid arthritis of unspecified site
- HCC (V28)
- HCC 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
- RAF reference coefficient
- 0.617
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work M05.40 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for M05.40
For M05.40, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- 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
Coder workflow notes
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What This Code Means
M05.40 is the ICD-10-CM diagnosis code for rheumatoid myopathy with rheumatoid arthritis of unspecified site. Muscle weakness and inflammation (myopathy) caused by rheumatoid arthritis when the specific joint location is not identified. M05.40 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, M05.40 maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders (HCC 93) with a source-labeled community, non-dual, aged reference coefficient of 0.617. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
Use this code only when the site of rheumatoid arthritis is unspecified or unknown. For M05.40, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, and MEAT documentation criteria for M05.40 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 site of rheumatoid arthritis is unspecified or unknown
- •Document the presence of myopathy (muscle involvement) in addition to the arthritis diagnosis
Clinical Significance
This diagnosis represents rheumatoid arthritis complicated by muscle weakness and inflammation (myopathy) when the specific joint site is not documented. Rheumatoid myopathy indicates systemic disease progression beyond joint involvement, affecting muscle tissue and requiring aggressive disease-modifying therapy and monitoring for functional decline and disability.
Documentation Requirements
- ✓Confirmed diagnosis of rheumatoid arthritis with positive serology (RF or anti-CCP)
- ✓Clinical evidence of muscle weakness, atrophy, or inflammatory myopathy
- ✓Documentation of muscle enzyme elevation (CK, aldolase) or muscle biopsy findings
- ✓Electromyography or nerve conduction studies showing myopathy
- ✓Assessment of functional limitations related to muscle weakness
- ✓Laboratory evidence of systemic inflammation (elevated ESR, CRP)
- ✓Documentation of chronicity and ongoing disease activity
- ✓Treatment with DMARDs or biologic agents
Commonly Confused Codes
- •M05.41-M05.49: Rheumatoid myopathy with specific joint site documentation (more specific when known)
- •G72.9: Myopathy, unspecified (not related to rheumatoid arthritis)
- •M60.9: Myositis, unspecified (different inflammatory muscle condition)
- •M06.9: Rheumatoid arthritis, unspecified (no myopathy involvement documented)