2026 ICD-10-CM Diagnosis Code B01.12Varicella myelitis

ICD-10-CM Codes›A00–B99›B00-B09›B01

ICD-10-CM B01.12
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

B01.12 is a billable ICD-10-CM diagnosis code for varicella myelitis. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). Coders also document this condition as post-infective myelitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Viral infection.

Code Identity

ICD-10-CM Code
B01.12
Billable Status
Yes — Valid for Submission
Code Describes
Varicella myelitis
Short Description
Varicella myelitis
Same as the full description in the CMS dataset.
Parent Code
B01.1
Varicella encephalitis, myelitis and encephalomyelitis

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB00-B09Viral infections characterized by skin and mucous membrane lesions
CategoryB01Varicella [chickenpox]
This CodeB01.12Varicella myelitis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Post-infective myelitis
  • Postvaricella myelitis

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Postchickenpox myelitis

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.

    • Myelitis(acute) (ascending) (childhood) (chronic) (descending) (diffuse) (disseminated) (idiopathic) (pressure) (progressive) (spinal cord) (subacute)
      • postchickenpox
    • Myelitis(acute) (ascending) (childhood) (chronic) (descending) (diffuse) (disseminated) (idiopathic) (pressure) (progressive) (spinal cord) (subacute)
      • varicella
    • Varicella
      • with
        • myelitis

Clinical ClassificationClinical

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

CCSR INF008
Viral infection
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Chickenpox

Chickenpox is an infection caused by the varicella-zoster virus. Most cases are in children under age 15, but older children and adults can get it. It spreads very easily from one person to another.

Read the full article at MedlinePlus

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

Convert B01.12 to ICD-9-CMHistory

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

ICD-9-CM
052.2 Postvaricella myelitis
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 B01.12Overview

Is B01.12 (Varicella encephalitis, myelitis and encephalomyelitis) a billable code?

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

What is the ICD-9 equivalent of B01.12?

Under the General Equivalence Mappings, varicella myelitis converts to ICD-9-CM 052.2 (postvaricella myelitis). 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.