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B26.2 ICD-10-CM Code: Mumps encephalitis

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Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Official instructions
2 inclusion terms

What these terms mean →

Billable · FY2027A valid, specific ICD-10-CM code, reportable for dates of service in FY2027.

What you need to know

Source: CMS/NCHS Official ICD-10-CM tabular notes, quoted. From the CMS/NCHS tabular list for the release in force. A note the category or block publishes applies to this code too, and is marked with where it comes from.

Includesfrom B26What B26 covers
  • epidemic parotitis
  • infectious parotitis

Where it sits Source: CMS/NCHS

Under:Chapter 1: Certain Infectious and Parasitic DiseasesB25-B34 Other viral diseasesB26 Mumps

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Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v44, Appendix B.

  • MS-DRG 023 — CRANIOTOMY WITH MAJOR DEVICE IMPLANT OR ACUTE COMPLEX CNS PRINCIPAL DIAGNOSIS WITH MCC OR ANTINEOPLASTIC IMPLANT OR EPILEPSY WITH NEUROSTIMULATOR (MDC 01)
  • MS-DRG 024 — CRANIOTOMY WITH MAJOR DEVICE IMPLANT OR ACUTE COMPLEX CNS PRINCIPAL DIAGNOSIS WITHOUT MCC (MDC 01)
  • MS-DRG 097 — NON-BACTERIAL INFECTION OF NERVOUS SYSTEM EXCEPT VIRAL MENINGITIS WITH MCC (MDC 01)
  • MS-DRG 098 — NON-BACTERIAL INFECTION OF NERVOUS SYSTEM EXCEPT VIRAL MENINGITIS WITH CC (MDC 01)
  • MS-DRG 099 — NON-BACTERIAL INFECTION OF NERVOUS SYSTEM EXCEPT VIRAL MENINGITIS WITHOUT CC/MCC (MDC 01)
  • MS-DRG 791 — PREMATURITY WITH MAJOR PROBLEMS (MDC 15)
  • MS-DRG 793 — FULL TERM NEONATE WITH MAJOR PROBLEMS (MDC 15)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for B26.2 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2027Effective: October 1, 2026

Trace:FY2027 changesChange historyRelease, file and checksum

Notes without a marker are published on B26.2 itself; “inherited from” names the category or block whose note applies here.

Includes

Conditions the official ICD-10-CM tabular list includes under this code.

  • epidemic parotitis
  • infectious parotitis

Source: inherited from B26

Coding context

Guidelines, coding notes, decision aids, relationships (with MS-DRG and CCSR classification), hierarchy, HCC, coverage and the context map: what a coder reaches for after the core. Each section names whether it is official source data, a MedCoder-derived relationship or MedCoder editorial.

Code Overview

Mumps encephalitis is a billable ICD-10-CM diagnosis code (B26.2).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Verify Before Coding

  • MCC as a secondary diagnosis (FY2027). Can raise the stay's MS-DRG severity tier.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder-derived relationships — computed from published CMS and AHRQ datasets

Other codes that name B26.2 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 3 Excludes1 notes across 3 chapters: A85 — Other viral encephalitis, not elsewhere classified, G05 — Encephalitis, myelitis and encephalomyelitis in diseases classified elsewhere, K11.2 — Sialoadenitis (via B26.-).

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 1 Code First instruction: H67 — Otitis media in diseases classified elsewhere (via B26.-).

Each of these codes carries a Code First note naming this condition — when that code is reported, THIS code is sequenced first, ahead of it.

MS-DRG Grouper Relationships (FY2027)

Potential MS-DRG participation — not a DRG assignment.

FY2027 MS-DRG: MCC — Major Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 23 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 7 MS-DRGs: DRG 023 (MDC 01), DRG 024 (MDC 01), DRG 097 (MDC 01), DRG 098 (MDC 01), DRG 099 (MDC 01), DRG 791 (MDC 15), DRG 793 (MDC 15).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):NVS002 — Encephalitis (default); INF008 — Viral infection.

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical process (MS-DRG)

Acts as MCC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

A74.81 — Chlamydial peritonitis, A74.89 — Other chlamydial diseases, A74.9 — Chlamydial infection, unspecified, A96.2 — Lassa fever, A98.3 — Marburg virus disease, A98.4 — Ebola virus disease, B26.82 — Mumps myocarditis, B26.83 — Mumps nephritis, B26.85 — Mumps arthritis, B26.89 — Other mumps complications, B26.9 — Mumps without complication, B33.24 — Viral cardiomyopathy, B33.4 — Hantavirus (cardio)-pulmonary syndrome [HPS] [HCPS], B33.8 — Other specified viral diseases, B34.1 — Enterovirus infection, unspecified, B34.2 — Coronavirus infection, unspecified, B34.4 — Papovavirus infection, unspecified, B34.8 — Other viral infections of unspecified site, B92 — Sequelae of leprosy, B94.2 — Sequelae of viral hepatitis, +2 more

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical categories (Encephalitis, Viral infection).

A86 — Unspecified viral encephalitis, A92.2 — Venezuelan equine fever, A92.31 — West Nile virus infection with encephalitis, B00.4 — Herpesviral encephalitis, B01.11 — Varicella encephalitis and encephalomyelitis, B02.0 — Zoster encephalitis, B05.0 — Measles complicated by encephalitis, B06.01 — Rubella encephalitis, B10.01 — Human herpesvirus 6 encephalitis, B10.09 — Other human herpesvirus encephalitis, B40.81 — Blastomycotic meningoencephalitis, B57.42 — Meningoencephalitis in Chagas' disease, B58.2 — Toxoplasma meningoencephalitis, B60.11 — Meningoencephalitis due to Acanthamoeba (culbertsoni), G04.00 — Acute disseminated encephalitis and encephalomyelitis, unspecified, G04.01 — Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM), G04.02 — Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis, G04.2 — Bacterial meningoencephalitis and meningomyelitis, not elsewhere classified, G04.30 — Acute necrotizing hemorrhagic encephalopathy, unspecified, G04.31 — Postinfectious acute necrotizing hemorrhagic encephalopathy, +314 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main terms “Meningoencephalitis”, “Encephalitis”; these codes share that main term but sit in a different category of the Tabular List.

B00.4 — Herpesviral encephalitis (herpesviral), B01.11 — Varicella encephalitis and encephalomyelitis (postvaricella), B02.0 — Zoster encephalitis (in, zoster), B05.0 — Measles complicated by encephalitis (postmeasles), B06.01 — Rubella encephalitis (in, rubella), B09 — Unspecified viral infection characterized by skin and mucous membrane lesions (postexanthematous NEC), B10.01 — Human herpesvirus 6 encephalitis (herpesviral, due to herpesvirus 6), B10.09 — Other human herpesvirus encephalitis (herpesviral, specified NEC), B20 — Human immunodeficiency virus [HIV] disease (due to, human immunodeficiency virusdisease), B25.8 — Other cytomegaloviral diseases (in, cytomegalovirus), B40.81 — Blastomycotic meningoencephalitis (in, blastomycosis NEC), B45.1 — Cerebral cryptococcosis (Torula, torular), B56.9 — African trypanosomiasis, unspecified (in, African trypanosomiasis), B57.42 — Meningoencephalitis in Chagas' disease (in, Chagas' disease), B58.2 — Toxoplasma meningoencephalitis (in, toxoplasmosis), B60.2 — Naegleriasis (in, naegleriasis), B71.9 — Cestode infection, unspecified (parasitic NOS), B75 — Trichinellosis (trichinosis), B83.2 — Angiostrongyliasis due to Parastrongylus cantonensis (eosinophilic), B89 — Unspecified parasitic disease (parasitic NEC), +49 more

Contextual Map

Every relationship of B26.2 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run B26.2 with these 4 related codes in Claim Check

Hierarchy

Referenced by Excludes1 notes

Referenced by Code First instructions

Clinical classification (CCSR)

MS-DRG Grouper

MDC crossing

  • MDC 01 — Diseases and Disorders of the Nervous System[MDC crossing]: “Diseases and Disorders of the Nervous System — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 8,919 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2027
  • MDC 15 — Newborns and Other Neonates with Conditions Originating in Perinatal Period[MDC crossing]: “Newborns and Other Neonates with Conditions Originating in Perinatal Period — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs.”— CMS MS-DRG Definitions Manual · FY2027

Index entries

  • Encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute), in (due to), mumps[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2027
  • Meningoencephalitis, in (due to), mumps[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2027
  • Meningoencephalitis, mumps[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2027
  • Mumps, encephalitis[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2027
  • Mumps, meningoencephalitis[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2027

Nearest codes (12)

Change history

  • FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Reference

Index terms and tables, published questions and FAQ, every source behind this page with its release and checksum, the date-of-service check and the complete change history.

Indexed Clinical Terms (5)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2027 tabular list, index and tables, effective October 1, 2026 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v44.0 (October 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v44 Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder-derived relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder editorial explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Current data releases:ICD-10-CM FY2027 · ICD-10-PCS FY2027 · HCPCS October 2026 · MS-DRG v44 · Medicare Code Editor v44.0 · NCCI PTP Q4 2026 · MUE Q4 2026 · NCD code lists 2026-01 · LCD export September 28, 2026 · All releases and sources

Labels on this page: Official source data · MedCoder-derived relationship · MedCoder editorial explanation. How to read the labels · All data sources and release dates · CMS coding rules

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "B26.2 — Mumps encephalitis." ICD-10-CM FY2027. https://medcoder.ai/icd10/code/b26.2-mumps-encephalitis

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Mumps encephalitis

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027, and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to B26.2 in its code family, with their registry titles.

View all codes in the B26 family