What is ICD-10 code M04.1?

M04.1 is the ICD-10-CM diagnosis code for Periodic fever syndromes. A group of rare genetic conditions characterized by recurring episodes of fever and inflammation throughout the body. It belongs to the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99). M04.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M04.1 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. M04.1 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. M04.1 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 should coders know when reporting M04.1?

Periodic fever syndromes are autoinflammatory disorders; ensure documentation distinguishes these from autoimmune conditions Specify the type of periodic fever syndrome if documented (such as PFAPA, FMF, or other variants) for more precise coding Because M04.1 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.

2026 ICD-10-CM M04.1: Periodic fever syndromes

ICD-10-CM Code View

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Code lookupM04.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Autoinflammatory syndromes (M04)

M04.1

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

Periodic fever syndromes

A group of rare genetic conditions characterized by recurring episodes of fever and inflammation throughout the body.

Buddy Insight

This represents periodic fever syndromes, rare autoinflammatory conditions characterized by recurrent episodes of fever and systemic inflammation.

CMS-HCC V28

Mapped

HCC 94

Systemic Lupus Erythematosus ...

RAF 0.268

CMS-HCC V24

Mapped

HCC 40

Rheumatoid Arthritis and Infl...

RAF 0.421

ACA/HHS

Mapped

HCC 57

HHS-HCC 57

Varies by metal level

ESRD/PACE

Mapped

HCC 40

Rheumatoid Arthritis and Infl...

RAF 0.058

RXHCC

Mapped

HCC 83

Rheumatoid Arthritis and Infl...

RAF 0.222

Code Book Path

Official

M04Autoinflammatory syndromes

M04.1Periodic fever syndromes

Inclusion Terms

Official

Familial Mediterranean fever
Hyperimmunoglobin D syndrome
Mevalonate kinase deficiency
Tumor necrosis factor receptor associated periodic syndrome [TRAPS]

Excludes 2

Official

Crohn's disease (K50.-)

Related Child Codes

Official

M04.2Cryopyrin-associated periodic syndromes

M04.8Other autoinflammatory syndromes

M04.9Autoinflammatory syndrome, unspecified

Includes

Official

ICD-10-CM does not list Includes notes for M04.1 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M04.1 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M04.1 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M04.1 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M04.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation of recurrent fever episodes with characteristic patterns

Evidence of systemic inflammatory symptoms during fever episodes

Exclusion of infectious causes for recurrent fevers

Clinical assessment supporting autoinflammatory syndrome diagnosis

MEAT Support

HCC Buddy guidance

Documentation of recurrent fever episodes with characteristic patterns

Evidence of systemic inflammatory symptoms during fever episodes

Exclusion of infectious causes for recurrent fevers

Clinical assessment supporting autoinflammatory syndrome diagnosis

Audit Caution

HCC Buddy guidance

Using for simple recurrent infections rather than true autoinflammatory syndromes

Confusing with infectious causes of recurrent fever

Missing the need for specific syndrome coding when known (e.g., FMF, TRAPS)

Using without adequate documentation of periodic/episodic nature

Common Mistakes

HCC Buddy guidance

R50.9 — Fever, unspecified (symptom vs specific syndrome diagnosis)

M04.2 — Cryopyrin-associated periodic syndromes (specific vs general periodic fever)

D89.1 — Cryoglobulinemia (different autoinflammatory mechanism)

M35.9 — Systemic involvement of connective tissue, unspecified (autoimmune vs autoinflammatory)

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 M04.1 an HCC code?

Yes. M04.1 (Periodic fever syndromes) maps to Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders under the CMS-HCC V28 risk adjustment model (and Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under V24), with a community non-dual aged RAF of 0.268. It is billable for payment year 2026.

Coder answer: M04.1 is billable and maps to V28 HCC 94, Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: M04.1
Description: Periodic fever syndromes
HCC (V28): HCC 94 — Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders
RAF: 0.268
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 94, Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders

0.268

V24HCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.421

ESRDHCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.058

RxHCCHCC 83, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

0.222

Each model's RAF is its CMS base weight for that model's standard population, so 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 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.

Work M04.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for M04.1

For M04.1 to 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 M04.1 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

M04.1 is the ICD-10-CM diagnosis code for periodic fever syndromes. A group of rare genetic conditions characterized by recurring episodes of fever and inflammation throughout the body. M04.1 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, M04.1 maps to Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders (HCC 94) with a community, non-dual, aged base RAF weight of 0.268. Under the older CMS-HCC V24 model, M04.1 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 40) with a community, non-dual, aged base RAF weight of 0.421. 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.

Periodic fever syndromes are autoinflammatory disorders; ensure documentation distinguishes these from autoimmune conditions. Because M04.1 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 M04.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Periodic fever syndromes are autoinflammatory disorders; ensure documentation distinguishes these from autoimmune conditions
•Specify the type of periodic fever syndrome if documented (such as PFAPA, FMF, or other variants) for more precise coding

Clinical Significance

This represents periodic fever syndromes, rare autoinflammatory conditions characterized by recurrent episodes of fever and systemic inflammation. These conditions require specialized management and monitoring due to their chronic nature and potential for serious complications including organ damage and amyloidosis.

Documentation Requirements

✓Documentation of recurrent fever episodes with characteristic patterns
✓Evidence of systemic inflammatory symptoms during fever episodes
✓Exclusion of infectious causes for recurrent fevers
✓Clinical assessment supporting autoinflammatory syndrome diagnosis
✓Documentation of fever periodicity and episode characteristics
✓Laboratory evidence of inflammation during acute episodes
✓Family history assessment for hereditary periodic fever syndromes
✓Response to specific treatments (colchicine, biologics) if applicable

Commonly Confused Codes

•R50.9: Fever, unspecified (symptom vs specific syndrome diagnosis)
•M04.2: Cryopyrin-associated periodic syndromes (specific vs general periodic fever)
•D89.1: Cryoglobulinemia (different autoinflammatory mechanism)
•M35.9: Systemic involvement of connective tissue, unspecified (autoimmune vs autoinflammatory)
•A49.9: Bacterial infection, unspecified (infectious vs autoinflammatory fever)