2026 ICD-10-CM Diagnosis Code M85.2Hyperostosis of skull

ICD-10-CM Codes›M00–M99›M80-M85›M85

ICD-10-CM M85.2
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M85.2 is a billable ICD-10-CM diagnosis code for hyperostosis of skull. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 564 through 566. Coders also document this condition as hyperostosis interna frontalis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified bone disease and musculoskeletal deformities.

Code Identity

ICD-10-CM Code
M85.2
Billable Status
Yes — Valid for Submission
Code Describes
Hyperostosis of skull
Short Description
Hyperostosis of skull
Same as the full description in the CMS dataset.
Parent Code
M85
Other disorders of bone density and structure

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 CodeM85.2Hyperostosis of skull

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Hyperostosis interna frontalis
  • Hyperostosis of skull
  • Large head
  • Leonine facies
  • Leontiasis
  • Leontiasis ossium
  • Stewart-Morel-Morgagni 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.

    • Buchem's syndrome(hyperostosis corticalis)
    • Craniopathy, metabolic
    • Disease, diseased
      • Morgagni's (syndrome) (hyperostosis frontalis interna)
    • Disorder(of)
      • bone
        • density and structure
          • hyperostosis of skull
    • Hyperostosis(monomelic)
      • cortical (skull)
    • Hyperostosis(monomelic)
      • frontal, internal of skull
    • Hyperostosis(monomelic)
      • interna frontalis
    • Hyperostosis(monomelic)
      • skull
    • Leontiasis
      • ossium
    • Morel(-Stewart)(-Morgagni) syndrome
    • Morel-Moore syndrome
    • Morgagni's
      • syndrome
    • Morgagni-Stewart-Morel syndrome
    • Stewart-Morel syndrome
    • Syndrome
      • Buchem's
    • Syndrome
      • Morel-Moore
    • Syndrome
      • Morel-Morgagni
    • Syndrome
      • Morgagni (-Morel) (-Stewart)
    • Syndrome
      • Stewart-Morel
    • Syndrome
      • van Buchem's
    • Van Buchem's syndrome

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

  • Hyperostosis of Skull

    hyperostosis of the bones of the skull.

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 M85.2 to ICD-9-CMHistory

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

ICD-9-CM
733.3 Hyperostosis of skull
Exact Match The mapping is direct, with no qualifiers.

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 M85.2Overview

Is M85.2 (Other disorders of bone density and structure) a billable code?

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

What MS-DRG does M85.2 group to?

When hyperostosis of skull is the principal diagnosis on an inpatient stay, it groups to MS-DRG 564, 565, 566, with relative weights from 0.7493 to 1.5436 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M85.2?

Under the General Equivalence Mappings, hyperostosis of skull converts to ICD-9-CM 733.3 (hyperostosis of skull). The mapping is a direct match.

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.