M04.8
BillableOther autoinflammatory syndromes
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M04.8 an HCC code?
Yes. M04.8 maps to Reactive and Specified Arthropathies 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 M04.8
For M04.8to 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 M04.8 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M04.8 is the ICD-10-CM diagnosis code for other autoinflammatory syndromes. Other rare genetic conditions characterized by abnormal immune system activation that causes recurrent inflammation and fever not classified elsewhere. M04.8 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering autoinflammatory syndromes (m04).
Under the CMS-HCC V28 risk adjustment model, M04.8 maps to Reactive and Specified Arthropathies (HCC 94) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, M04.8 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.
This is a catch-all code for autoinflammatory syndromes not specifically classified; document the specific syndrome name when possible. Because M04.8 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 M04.8 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
Clinical Significance
This represents other autoinflammatory syndromes not elsewhere classified, including rare genetic conditions characterized by abnormal activation of the innate immune system. These conditions require specialized diagnosis and treatment, often with immunosuppressive or biologic therapies to control inflammation and prevent complications.
Documentation Requirements
- ✓Documentation of specific autoinflammatory syndrome diagnosis
- ✓Evidence of recurrent inflammatory episodes
- ✓Genetic testing results when available and applicable
- ✓Exclusion of infectious and autoimmune causes
- ✓Documentation of characteristic clinical features
- ✓Laboratory evidence of systemic inflammation
- ✓Family history assessment for hereditary patterns
- ✓Response to specific treatments (anti-inflammatory, immunosuppressive)
Commonly Confused Codes
- •M04.1 — Periodic fever syndromes (when specific syndrome doesn't fit periodic pattern)
- •M04.2 — Cryopyrin-associated periodic syndromes (when not cryopyrin-related)
- •M35.9 — Systemic involvement of connective tissue, unspecified (autoimmune vs autoinflammatory)
- •D89.89 — Other specified disorders involving the immune mechanism
- •M79.89 — Other specified soft tissue disorders