2026 ICD-10-CM Diagnosis Code M05.40Rheumatoid myopathy with rheumatoid arthritis of unspecified site

ICD-10-CM Codes›M00–M99›M05-M14›M05

ICD-10-CM M05.40
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M05.40 is a billable ICD-10-CM diagnosis code for rheumatoid myopathy with rheumatoid arthritis of unspecified site. 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. The code is flagged as an unspecified code, since codes identifying laterality exist in the same family. Coders also document this condition as myopathy due to rheumatoid arthritis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Myopathies and Rheumatoid arthritis and related disease.

Code Identity

ICD-10-CM Code
M05.40
Billable Status
Yes — Valid for Submission
Code Describes
Rheumatoid myopathy with rheumatoid arthritis of unspecified site
Short Description
Rheumatoid myopathy with rheumatoid arthritis of unsp site
Parent Code
M05.4
Rheumatoid myopathy with rheumatoid arthritis

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM05-M14Inflammatory polyarthropathies
CategoryM05Rheumatoid arthritis with rheumatoid factor
This CodeM05.40Rheumatoid myopathy with rheumatoid arthritis of unspecified site

Code EditsBilling

Medicare Code Editor checks that affect claim validity for M05.40.

Unspecified codes
Unspecified codes exist in the ICD-10-CM classification for circumstances when documentation in the medical record does not provide the level of detail needed to support reporting a more specific code. However, in the inpatient setting, there should generally be very limited and rare circumstances for which the laterality (right, left, bilateral) of a condition is unable to be documented and reported. The following pages contain the list of unspecified ICD-10-CM diagnosis codes for which there is a more specific code to identify laterality (right, left, bilateral) within that code family.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Myopathy due to rheumatoid arthritis

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.

    • Rheumatoid
      • myopathy

Clinical ClassificationClinical

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

CCSR NVS018
Myopathies
Default principal diagnosis: inpatient No · outpatient No
CCSR MUS003
Rheumatoid arthritis and related disease
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a form of arthritis that causes pain, swelling, and stiffness in your joints. RA is an autoimmune disease. Although it is most common in the wrist and fingers, this disease can cause your immune system to attack any joint tissue. The inflammation (swelling) that comes with RA can also affect other body parts.

The full article covers:

  • What is rheumatoid arthritis?
  • Who is more likely to get rheumatoid arthritis?
  • What causes rheumatoid arthritis?
  • What are the symptoms of rheumatoid arthritis?
  • How is rheumatoid arthritis diagnosed?
  • What are the treatments for rheumatoid arthritis?

Read the full article at MedlinePlus

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

Convert M05.40 to ICD-9-CMHistory

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

ICD-9-CM
714.0 Rheumatoid arthritis
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.
ICD-9-CM
359.6 Infl myopathy in oth dis
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.

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 M05.40Overview

Is M05.40 (Rheumatoid myopathy with rheumatoid arthritis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report rheumatoid myopathy with rheumatoid arthritis of unspecified site on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M05.40 group to?

When rheumatoid myopathy with rheumatoid arthritis of unspecified site 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 M05.40?

Under the General Equivalence Mappings, rheumatoid myopathy with rheumatoid arthritis of unspecified site converts to ICD-9-CM 714.0 (rheumatoid arthritis) and 359.6 (infl myopathy in oth dis). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.