M35.1
BillableOther overlap syndromes
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M35.1 an HCC code?
Yes. M35.1 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under the V24 model but is not retained in V28.
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 M35.1
For M35.1to 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 M35.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M35.1 is the ICD-10-CM diagnosis code for other overlap syndromes. Other overlap syndromes refers to conditions where a patient has features of multiple autoimmune diseases that don't fit neatly into a single diagnosis category. M35.1 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering systemic connective tissue disorders (m30-m36).
Under the older CMS-HCC V24 model, M35.1 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 40) with a community, non-dual, aged base RAF weight of 0.307. 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 when documentation shows characteristics of multiple connective tissue diseases but doesn't meet criteria for a specific overlap syndrome. Because M35.1 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 M35.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code when documentation shows characteristics of multiple connective tissue diseases but doesn't meet criteria for a specific overlap syndrome
- •Document which specific autoimmune features are present to justify the overlap syndrome diagnosis
Clinical Significance
Other overlap syndromes represent complex multi-system autoimmune conditions that don't fit classic disease patterns, requiring specialized rheumatologic care and frequent monitoring. These conditions often have unpredictable courses and may evolve into more defined connective tissue diseases over time.
Documentation Requirements
- ✓Documentation of features from multiple autoimmune/connective tissue diseases
- ✓Specific clinical manifestations that don't meet criteria for single disease entity
- ✓Laboratory evidence supporting mixed or overlapping autoimmune processes
- ✓Exclusion of defined connective tissue diseases (SLE, scleroderma, etc.)
- ✓Description of organ systems involved and severity of involvement
- ✓Immunologic markers and autoantibody profiles
- ✓Treatment response and disease progression documentation
Excludes 1 — Do NOT code together
- polyangiitis overlap syndrome (M30.8)
Commonly Confused Codes
- •M32.9 — Systemic lupus erythematosus, unspecified (single defined disease)
- •M34.9 — Systemic sclerosis, unspecified (single defined disease)
- •M33.90 — Dermatopolymyositis, unspecified (single defined disease)
- •M35.9 — Systemic involvement of connective tissue, unspecified (less specific)
- •M79.3 — Panniculitis, unspecified (localized condition)