2026 ICD-10-CM Diagnosis Code M88.859Osteitis deformans of unspecified thigh

ICD-10-CM Codes›M00–M99›M86-M90›M88

ICD-10-CM M88.859
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M88.859 is a billable ICD-10-CM diagnosis code for osteitis deformans of unspecified thigh. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 553 through 554. Coders also document this condition as Paget's disease-femur. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified bone disease and musculoskeletal deformities.

Code Identity

ICD-10-CM Code
M88.859
Billable Status
Yes — Valid for Submission
Code Describes
Osteitis deformans of unspecified thigh
Short Description
Osteitis deformans of unspecified thigh
Same as the full description in the CMS dataset.
Parent Code
M88.85
Osteitis deformans of thigh

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM86-M90Other osteopathies
CategoryM88Osteitis deformans [Paget's disease of bone]
This CodeM88.859Osteitis deformans of unspecified thigh

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Paget's disease-femur

Clinical ClassificationClinical

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

CCSR MUS028
Other specified bone disease and musculoskeletal deformities
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Paget's Disease of Bone

Paget's disease of bone is a chronic bone disorder. Normally, there is a process in which your bones break down and then regrow. In Paget's disease, this process is abnormal. There is excessive breakdown and regrowth of bone. Because the bones regrow too quickly, they are bigger and softer than normal.

The full article covers:

  • What is Paget's disease of bone?
  • What causes Paget's disease of bone?
  • Who is at risk for Paget's disease of bone?
  • What are the symptoms of Paget's disease of bone?
  • What other problems can Paget's disease of bone cause?
  • How is Paget's disease of bone diagnosed?
  • What are the treatments for Paget's disease of bone?

Read the full article at MedlinePlus

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

Convert M88.859 to ICD-9-CMHistory

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

ICD-9-CM
731.0 Osteitis deformans NOS
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 M88.859Overview

Is M88.859 (Osteitis deformans of thigh) a billable code?

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

What MS-DRG does M88.859 group to?

When osteitis deformans of unspecified thigh is the principal diagnosis on an inpatient stay, it groups to MS-DRG 553, 554, with relative weights from 0.8301 to 1.2963 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M88.859?

Under the General Equivalence Mappings, osteitis deformans of unspecified thigh converts to ICD-9-CM 731.0 (osteitis deformans NOS). 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.