2026 ICD-10-CM Diagnosis Code M04.1Periodic fever syndromes

ICD-10-CM Codes›M00–M99›M04›M04

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

M04.1 is a billable ICD-10-CM diagnosis code for periodic fever syndromes. 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. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Autoinflammatory syndromes.

For Medicare Advantage risk adjustment, M04.1 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
M04.1
Billable Status
Yes — Valid for Submission
Code Describes
Periodic fever syndromes
Short Description
Periodic fever syndromes
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 CodeM04.1Periodic fever syndromes

Medicare Risk Adjustment (HCC)Billing

M04.1 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Superseded by HCC 93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.

  • Amyloid of familial Mediterranean fever
  • Aphthous ulcer of mouth
  • Cervical lymphadenitis
  • Complex multigenic autoinflammatory syndrome
  • Congenital sideroblastic anemia, B-cell immunodeficiency, periodic fever, developmental delay syndrome
  • Deficiency of mevalonate kinase
  • Familial Mediterranean fever
  • Hemophagocytic lymphohistiocytosis
  • Hereditary periodic fever
  • Hyperimmunoglobulinemia D with periodic fever
  • Macrophage activation syndrome
  • Menstrual cycle dependent periodic fever
  • NLRC4-related familial cold autoinflammatory syndrome
  • NLRP12-associated hereditary periodic fever syndrome
  • Pericarditis due to familial Mediterranean fever
  • Periodic fever, infantile enterocolitis, autoinflammatory syndrome
  • PFAPA syndrome
  • Recurrent aphthous ulcer
  • Recurrent ulcer of mouth
  • Secondary systemic amyloidosis
  • TNF receptor-associated periodic fever syndrome

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

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

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

  • Familial Mediterranean Fever

    a group of hereditary autoinflammation diseases, characterized by recurrent fever, abdominal pain, headache, rash, pleurisy; and arthritis. orchitis; benign meningitis; and amyloidosis may also occur. homozygous or compound heterozygous mutations in marenostrin gene encoding pyrin result in autosomal recessive transmission; simple heterozygous, autosomal dominant form of the disease also exists with mutations in the same gene.

  • 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.

  • Cervical Lymphadenitis

    inflammation of the cervical lymph nodes.

Convert M04.1 to ICD-9-CMHistory

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

ICD-9-CM
277.31 Fam Mediterranean fever
Approximate The match is approximate rather than exact.

Code History & ChangesHistory

Replacement M04.1 replaces the following previously assigned code(s):

  • E85.0 - Non-neuropathic heredofamilial amyloidosis
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 M04.1Overview

What is the ICD-10 code for periodic fever syndromes?

The ICD-10-CM code for periodic fever syndromes is M04.1 (sometimes written as M041). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Is M04.1 (Autoinflammatory syndromes) a billable code?

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

What MS-DRG does M04.1 group to?

When periodic fever syndromes 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 M04.1?

Under the General Equivalence Mappings, periodic fever syndromes converts to ICD-9-CM 277.31 (fam Mediterranean fever). The mapping is approximate, so confirm the match fits the documentation.

What HCC is M04.1?

M04.1 (periodic fever syndromes) 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 M04.1 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, M04.1 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.