2026 ICD-10-CM Diagnosis Code M35.4Diffuse (eosinophilic) fasciitis

ICD-10-CM Codes›M00–M99›M30-M36›M35

ICD-10-CM M35.4
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M35.4 is a billable ICD-10-CM diagnosis code for diffuse (eosinophilic) fasciitis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 557 through 558. Coders also document this condition as eosinophilic fasciitis caused by L-tryptophan. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Systemic lupus erythematosus and connective tissue disorders.

Code Identity

ICD-10-CM Code
M35.4
Billable Status
Yes — Valid for Submission
Code Describes
Diffuse (eosinophilic) fasciitis
Short Description
Diffuse (eosinophilic) fasciitis
Same as the full description in the CMS dataset.
Parent Code
M35
Other systemic involvement of connective tissue

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM30-M36Systemic connective tissue disorders
CategoryM35Other systemic involvement of connective tissue
This CodeM35.4Diffuse (eosinophilic) fasciitis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Eosinophilic fasciitis caused by L-tryptophan
  • Fasciitis with eosinophilia syndrome

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Fasciitis
      • diffuse (eosinophilic)

Clinical ClassificationClinical

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

CCSR MUS024
Systemic lupus erythematosus and connective tissue disorders
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Connective Tissue Disorders

Your connective tissue supports many different parts of your body, such as your skin, eyes, and heart. It is like a "cellular glue" that gives your body parts their shape and helps keep them strong. It also helps some of your tissues do their work. It is made of many kinds of proteins. Cartilage and fat are types of connective tissue.

Read the full article at MedlinePlus

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

Convert M35.4 to ICD-9-CMHistory

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

ICD-9-CM
728.89 Muscle/ligament dis NEC
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About M35.4Overview

Is M35.4 (Other systemic involvement of connective tissue) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report diffuse (eosinophilic) fasciitis on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M35.4 group to?

When diffuse (eosinophilic) fasciitis is the principal diagnosis on an inpatient stay, it groups to MS-DRG 557, 558, with relative weights from 0.8932 to 1.4869 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M35.4?

Under the General Equivalence Mappings, diffuse (eosinophilic) fasciitis converts to ICD-9-CM 728.89 (muscle/ligament dis NEC). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.