2026 ICD-10-CM Diagnosis Code M04.9Autoinflammatory syndrome, unspecified

ICD-10-CM Codes›M00–M99›M04›M04

ICD-10-CM M04.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M04.9 is a billable ICD-10-CM diagnosis code for autoinflammatory syndrome, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 545 through 547. Coders also document this condition as autoinflammatory disease. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Autoinflammatory syndromes.

For Medicare Advantage risk adjustment, M04.9 maps to CMS-HCC Category 94 (Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders) under the V28 model, adding a risk factor of about 0.268 for a community, non-dual, aged beneficiary in payment year 2026.

Code Identity

ICD-10-CM Code
M04.9
Billable Status
Yes — Valid for Submission
Code Describes
Autoinflammatory syndrome, unspecified
Short Description
Autoinflammatory syndrome, unspecified
Same as the full description in the CMS dataset.
Parent Code
M04
Autoinflammatory syndromes

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM04Autoinflammatory syndromes
CategoryM04Autoinflammatory syndromes
This CodeM04.9Autoinflammatory syndrome, unspecified

Medicare Risk Adjustment (HCC)Billing

M04.9 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.

CMS-HCC V28 Category (Payment Model)
HCC 94— Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders
Payment HCC · PY 2026 one of 71 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.268
community, non-dual, aged · ranges 0.196–0.297 across segments
Hierarchy
Superseded by HCC 93
a more severe related category takes the payment when both are reported
Prior Model (CMS-HCC V24)
HCC 40
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
PACE (CMS-HCC V22): HCC 40 · ESRD (V21): HCC 40 · ESRD (V24): HCC 40
ESRD V21 weights: 0.072 dialysis, 0.274–0.398 functioning graft · ESRD V24 weights: 0.058 dialysis, 0.284–0.414 functioning graft
Part D (RxHCC)
RxHCC 83 — Rheumatoid Arthritis and Other Inflammatory Polyarthropathy
also risk-adjusts in the Part D prescription drug model (V08)

Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Autoinflammatory disease
  • Early-onset autoimmunity, autoinflammation, immunodeficiency syndrome due to SOCS1 haploinsufficiency
  • Hemophagocytic lymphohistiocytosis
  • Macrophage activation syndrome
  • Periodic fever, infantile enterocolitis, autoinflammatory syndrome

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MUS036
Autoinflammatory syndromes
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Macrophage Activation Syndrome

    a serious complication of childhood systemic inflammatory disorders that is thought to be caused by excessive activation and proliferation of t-lymphocytes and macrophages. it is seen predominantly in children with systemic onset juvenile idiopathic arthritis.

  • Autoinflammation, Panniculitis, and Dermatosis Syndrome|AIPDS|ORAS|Otulin-Related Autoinflammatory Syndrome|Otulipenia

    an autosomal recessive condition caused by mutation(s) in the otulin gene, encoding ubiquitin thioesterase otulin. it is characterized by neonatal onset of recurrent fever, erythematous rash with painful nodules, painful joints, and lipodystrophy.

  • Autoinflammatory Syndrome

    a group of disorders of the innate immune system characterized by attacks of seemingly unprovoked inflammation without significant levels of either autoantibodies or autoreactive t cells more characteristic of autoimmune disease.

  • Familial Cold Autoinflammatory Syndrome|FCAS|FCAS

    an autoinflammatory disease caused by mutations in the nlrp3 gene which encodes cryopyrin. it is characterized by short episodes of fever, rash, and arthralgia after exposure to cold or rapid decrease in temperature.

  • NACHT, LRR and PYD Domains-Containing Protein 3|Angiotensin/Vasopressin Receptor AII/AVP-Like|Cold Autoinflammatory Syndrome 1 Protein|Cryopyrin|NLRP3|PYRIN-Containing APAF1-Like Protein 1

    nacht, lrr and pyd domains-containing protein 3 (1034 aa, ~118 kda) is encoded by the human nlrp3 gene. this protein plays a role in the modulation of both inflammation and apoptosis.

  • NEMO Deleted Exon 5 Autoinflammatory Syndrome|IKBKG/NEMO NDAS|NDAS

    an autoinflammatory syndrome caused by either gain-of-function splice site variants in the ikbkg gene resulting in a deletion in the c-terminal domain of the nemo (nf-kappa-b essential modulator) protein or by increased expression of an isoform lacking the domain encoded by exon 5. it is clinically distinct from the immunodeficiency syndromes caused by loss-of-function ikbkg mutations and has features more characteristic of chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (candle).

  • NLRP3 wt Allele|AGTAVPR|AII|AII/AVP|AVP|C1orf7|CIAS1|CLR1.1|Cold Autoinflammatory Syndrome 1 Gene|Cryopyrin Gene|FCAS|FCU|FLJ95925|MWS|NALP3|NLR Family, Pyrin Domain Containing 3 wt Allele|Nucleotide-Binding Oligomerization Domain, Leucine Rich Repeat and Pyrin Domain Containing 3 Gene|PYPAF1

    human nlrp3 wild-type allele is located in the vicinity of 1q44 and is approximately 33 kb in length. this allele, which encodes nacht, lrr and pyd domains-containing protein 3, is involved in the regulation of both apoptosis and inflammation. mutation of the gene is associated with familial cold autoinflammatory syndrome, muckle-wells syndrome, and chronic infantile neurological cutaneous and articular syndrome.

  • Proteasome-Associated Autoinflammatory Syndrome 1|CANDLE|CANDLE|Chronic Atypical Neutrophilic Dermatosis with Lipodystrophy and Elevated Temperature (CANDLE) Syndrome|Chronic Atypical Neutrophilic Dermatosis with Lipodystrophy and Elevated Temperature Syndrome|PRAAS1

    an autosomal recessive condition caused by mutation(s) in the psmb8 gene, encoding proteasome subunit beta type-8. it is characterized by early onset annular erythematous plaques, partial lipodystrophy, and recurrent fever.

Patient EducationClinical

Autoimmune Diseases

Your immune system protects you from disease and infection by attacking germs that get into your body, such as viruses and bacteria. Your immune system can tell that the germs aren't part of you, so it destroys them. If you have an autoimmune disease, your immune system attacks the healthy cells of your organs and tissues by mistake.

The full article covers:

  • What are autoimmune diseases?
  • What causes autoimmune diseases?
  • Who is at risk for autoimmune diseases?
  • What are the symptoms of autoimmune diseases?
  • How are autoimmune diseases diagnosed?
  • What are the treatments for autoimmune diseases?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert M04.9 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
710.9 Diff connect tis dis NOS
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2019AddedAdded to the ICD-10-CM code setEffective October 1, 2018.
FY 2020–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About M04.9Overview

What is the ICD-10 code for autoinflammatory syndrome, unspecified?

The ICD-10-CM code for autoinflammatory syndrome, unspecified is M04.9 (sometimes written as M049). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Is M04.9 (Autoinflammatory syndromes) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report autoinflammatory syndrome, unspecified on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M04.9 group to?

When autoinflammatory syndrome, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 545, 546, 547, with relative weights from 0.8362 to 2.4817 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M04.9?

Under the General Equivalence Mappings, autoinflammatory syndrome, unspecified converts to ICD-9-CM 710.9 (diff connect tis dis NOS). The mapping is approximate, so confirm the match fits the documentation.

What HCC is M04.9?

M04.9 (autoinflammatory syndrome, unspecified) maps to CMS-HCC Category 94 (Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders), commonly written as HCC 94, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 40 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 83.

Does M04.9 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, M04.9 adds a risk adjustment factor of about 0.268 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.196 to 0.297 depending on the payment segment). A more severe related category (HCC 93) supersedes it when both are reported. See the full factor table on the HCC 94 category page.