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B26.85 ICD-10-CM Code: Mumps arthritis

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

Coding at a Glance

Tabular directives
2 inclusion terms
Risk adjustment
CMS-HCC V28: 1 category · CMS-HCC V22 category 39

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 v43, Appendix B.

  • MS-DRG 791 — PREMATURITY WITH MAJOR PROBLEMS (MDC 15)
  • MS-DRG 793 — FULL TERM NEONATE WITH MAJOR PROBLEMS (MDC 15)
  • MS-DRG 865 — VIRAL ILLNESS WITH MCC (MDC 18)
  • MS-DRG 866 — VIRAL ILLNESS WITHOUT MCC (MDC 18)

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.

Risk Adjustment (CMS-HCC)

Payment categories this diagnosis maps to under CMS-HCC V28, payment year 2026.

  • HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis

Other models: CMS-HCC V22 HCC 39

Risk scores depend on the enrollee's full accepted diagnosis set and segment; a category mapping alone does not determine payment.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for B26.85 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on B26.85 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

Code Overview

Mumps arthritis is a billable ICD-10-CM diagnosis code (B26.85).

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

Indexed Clinical Terms (2)

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.

Verify Before Coding

  • CC as a secondary diagnosis (FY2026). 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 structured relationships — computed from published CMS and AHRQ datasets

Other codes that name B26.85 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 2 chapters: K11.2 — Sialoadenitis (via B26.-), M01 — Direct infections of joint in infectious and parasitic diseases classified elsewhere, M02 — Postinfective and reactive arthropathies.

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 (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: CC — 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 22 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 4 MS-DRGs: DRG 791 (MDC 15), DRG 793 (MDC 15), DRG 865 (MDC 18), DRG 866 (MDC 18).

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

Clinical classification (AHRQ CCSR):MUS001 — Infective arthritis (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 CC — 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, B26.89 — 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, B94.8 — Sequelae of other specified infectious and parasitic diseases, +1 more

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis) for risk-adjusted payment.

A39.84 — Postmeningococcal arthritis, A50.55 — Late congenital syphilitic arthropathy, A54.40 — Gonococcal infection of musculoskeletal system, unspecified, A54.41 — Gonococcal spondylopathy, A54.42 — Gonococcal arthritis, A54.43 — Gonococcal osteomyelitis, A54.49 — Gonococcal infection of other musculoskeletal tissue, A66.6 — Bone and joint lesions of yaws, A69.23 — Arthritis due to Lyme disease, B06.82 — Rubella arthritis, B42.82 — Sporotrichosis arthritis, M00.00 — Staphylococcal arthritis, unspecified joint, M00.011 — Staphylococcal arthritis, right shoulder, M00.012 — Staphylococcal arthritis, left shoulder, M00.019 — Staphylococcal arthritis, unspecified shoulder, M00.021 — Staphylococcal arthritis, right elbow, M00.022 — Staphylococcal arthritis, left elbow, M00.029 — Staphylococcal arthritis, unspecified elbow, M00.031 — Staphylococcal arthritis, right wrist, M00.032 — Staphylococcal arthritis, left wrist, +588 more

Same clinical category (CCSR)

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

A01.04 — Typhoid arthritis, A02.23 — Salmonella arthritis, A18.01 — Tuberculosis of spine, A18.02 — Tuberculous arthritis of other joints, A18.03 — Tuberculosis of other bones, A39.83 — Meningococcal arthritis, A54.42 — Gonococcal arthritis, A69.23 — Arthritis due to Lyme disease, B06.82 — Rubella arthritis, B42.82 — Sporotrichosis arthritis, M00.00 — Staphylococcal arthritis, unspecified joint, M00.011 — Staphylococcal arthritis, right shoulder, M00.012 — Staphylococcal arthritis, left shoulder, M00.019 — Staphylococcal arthritis, unspecified shoulder, M00.021 — Staphylococcal arthritis, right elbow, M00.022 — Staphylococcal arthritis, left elbow, M00.029 — Staphylococcal arthritis, unspecified elbow, M00.031 — Staphylococcal arthritis, right wrist, M00.032 — Staphylococcal arthritis, left wrist, M00.039 — Staphylococcal arthritis, unspecified wrist, +419 more

Same Index main term, other category

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

A39.83 — Meningococcal arthritis (meningococcal), A39.84 — Postmeningococcal arthritis (postmeningococcal), A46 — Erysipelas (due to or associated with, erysipelas), A49.9 — Bacterial infection, unspecified (in, bacterial disease), A50.55 — Late congenital syphilitic arthropathy (syphilitic, congenital), A52.16 — Charcôt's arthropathy (tabetic) (syphilitic), A54.42 — Gonococcal arthritis (gonococcal), A69.23 — Arthritis due to Lyme disease (in, Lyme disease), A92.1 — O'nyong-nyong fever (in, O'nyong-nyong), B06.82 — Rubella arthritis (rubella), B34.9 — Viral infection, unspecified (in, viral disease NEC), B42.82 — Sporotrichosis arthritis (in, sporotrichosis), B49 — Unspecified mycosis (mycotic NEC), B72 — Dracunculiasis (in, dracontiasis), B74.9 — Filariasis, unspecified (chylous), B83.9 — Helminthiasis, unspecified (in, helminthiasis NEC), B89 — Unspecified parasitic disease (in, parasitic disease NEC), B97.6 — Parvovirus as the cause of diseases classified elsewhere (due to or associated with, human parvovirus), C86.0 — Extranodal NK/T-cell lymphoma, nasal type (in, reticulosis, malignant), C90.0 — Multiple myeloma (in, myelomatosis), +194 more

Contextual Map

Every relationship of B26.85 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 B26.85 with these 4 related codes in Claim Check

Hierarchy

Referenced by Excludes1 notes

Referenced by Code First instructions

Clinical classification (CCSR)

Risk adjustment (CMS-HCC)

  • HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis [CMS-HCC]— CMS-HCC V28 · 2026

MS-DRG Grouper

MDC crossing

  • 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 · FY2026
  • MDC 18 — Infectious and Parasitic Diseases, Systemic or Unspecified Sites[MDC crossing]: “Infectious and Parasitic Diseases, Systemic or Unspecified Sites — 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. 1 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

  • Arthritis, arthritic (acute) (chronic) (nonpyogenic) (subacute), in (due to), mumps[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Mumps, arthritis[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

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

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 FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v43.1 (April 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 — v43 Release, file and checksum · Publisher’s page
Risk adjustment Official source data
2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release 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 structured 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 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.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

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. "B26.85 — Mumps arthritis." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/b26.85-mumps-arthritis

Change history

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

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027 (effective October 1, 2026), 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 B26.85 in its code family, with their registry titles.

View all codes in the B26 family