2026 ICD-10-CM Diagnosis Code M85.00Fibrous dysplasia (monostotic), unspecified site

ICD-10-CM Codes›M00–M99›M80-M85›M85

ICD-10-CM M85.00
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M85.00 is a billable ICD-10-CM diagnosis code for fibrous dysplasia (monostotic), unspecified site. 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 dysplasia epiphysealis hemimelica. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified bone disease and musculoskeletal deformities.

Code Identity

ICD-10-CM Code
M85.00
Billable Status
Yes — Valid for Submission
Code Describes
Fibrous dysplasia (monostotic), unspecified site
Short Description
Fibrous dysplasia (monostotic), unspecified site
Same as the full description in the CMS dataset.
Parent Code
M85.0
Fibrous dysplasia (monostotic)

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM80-M85Disorders of bone density and structure
CategoryM85Other disorders of bone density and structure
This CodeM85.00Fibrous dysplasia (monostotic), unspecified site

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Dysplasia epiphysealis hemimelica
  • Fibrous dysplasia of bone
  • Fibrous dysplasia of bone with intramuscular myxoma
  • Hyaline fibromatosis syndrome
  • Juvenile elastofibromatosis
  • Juvenile hyaline fibromatosis
  • Monostotic fibrous dysplasia
  • Non-ossifying fibroma

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.

    • Dysplasia
      • fibrous
        • bone NEC (monostotic)

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

Clinical InformationClinical

  • Fibrous Dysplasia of Bone

    a disease of bone marked by thinning of the cortex by fibrous tissue containing bony spicules, producing pain, disability, and gradually increasing deformity. only one bone may be involved (fibrous dysplasia, monostotic) or several (fibrous dysplasia, polyostotic).

  • Hyaline Fibromatosis Syndrome

    autosomal recessive disorder characterized by hyaline deposition in the skin, bone, gastrointestinal tract, muscles and glands; multiple subcutaneous skin nodules; gingival hypertrophy; and joint contractures. mutations in the capillary morphogenesis protein-2 are associated with the disorder.

Patient EducationClinical

Bone Diseases

Your bones help you move, give you shape and support your body. They are living tissues that rebuild constantly throughout your life. During childhood and your teens, your body adds new bone faster than it removes old bone. After about age 20, you can lose bone faster than you make bone.

Read the full article at MedlinePlus

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

Convert M85.00 to ICD-9-CMHistory

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

ICD-9-CM
733.29 Bone cyst 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 M85.00Overview

Is M85.00 (Fibrous dysplasia (monostotic)) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report fibrous dysplasia (monostotic), unspecified site on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M85.00 group to?

When fibrous dysplasia (monostotic), unspecified site 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 M85.00?

Under the General Equivalence Mappings, fibrous dysplasia (monostotic), unspecified site converts to ICD-9-CM 733.29 (bone cyst NEC). 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.