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M33.20 ICD-10-CM Code: Polymyositis, organ involvement unspecified

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

Coding at a Glance

Tabular directives
4 inclusion terms · 1 Excludes1
Risk adjustment
CMS-HCC V28: 1 category · CMS-HCC V22 category 40 · RxHCC V08 category 83

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 545 — CONNECTIVE TISSUE DISORDERS WITH MCC (MDC 08)
  • MS-DRG 546 — CONNECTIVE TISSUE DISORDERS WITH CC (MDC 08)
  • MS-DRG 547 — CONNECTIVE TISSUE DISORDERS WITHOUT CC/MCC (MDC 08)

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 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders (supersedes HCC 94)

Other models: CMS-HCC V22 HCC 40 · RxHCC V08 HCC 83

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 M33.20 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 M33.20 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.

  • autoimmune disease NOS
  • collagen (vascular) disease NOS
  • systemic autoimmune disease
  • systemic collagen (vascular) disease

Source: inherited from M30-M36

Excludes1 — Not Coded Here

Conditions generally not reported together with this code (Excludes1) -- an error unless the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

  • autoimmune disease, single organ or single cell-type -code to relevant condition category

Source: inherited from M30-M36

Coder workflow for M33.20

MedCoder structured workflow — derived from this code’s own official record

Before you code M33.20

  1. Unspecified does not mean incorrect. When the record gives no greater specificity, M33.20 may be the appropriate code. Check the record for detail that supports a more specific sibling — in this subcategory the siblings differ by the presence or absence of the associated condition. An unspecified code is for records that do not provide the detail a more specific code needs; a query, not an assumption, is the route to specificity (Guidelines I.A.9.b, I.B.18).

    ReviewM33.21, M33.22, M33.29

    See the relationships section · Guide: Other vs unspecified (NEC vs NOS) →

  2. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with M33.20. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

    See the official tabular notes

Choose the right path

  1. Does the record document the detail a more specific sibling code needs?
    Yes → Review the specific siblings in this subcategory.
    No → Continue — M33.20 is appropriate when the documentation goes no further.

    ReviewM33.21, M33.22, M33.29

  2. Does the documentation support a condition named in M33.20’s Excludes1 note?
    Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
    No → Continue.

Consider M33.20. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
The associated condition or complication
Whether the associated condition the title names is documented; the “with” convention presumes some links, and a provider statement that the conditions are unrelated defeats it (Guidelines I.A.15).
Any detail beyond this code’s title
What the record states that a more specific sibling code would capture — or its absence, which itself supports the unspecified code.

Official instructions as workflow

  • Excludes1 — check before selecting M33.20(1 note)

    Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with M33.20: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

    See the official tabular notes · Guidelines I.A.12.a

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: The provider documents the condition in the terms of this code’s title and records no further detail.

Coding question: Is a more specific sibling code supportable?

Path: Review the specific siblings in this subcategory and what each requires the record to state.

Reason: A more specific code needs documentation of the distinguishing element; without it the unspecified code is appropriate, and a provider query is the route to specificity (Guidelines I.A.9.b, I.B.18).

ReviewM33.21, M33.22, M33.29

Documentation: Both the condition M33.20 describes and a condition named in its Excludes1 note are documented for the same encounter.

Coding question: Can both codes be reported?

Path: Review the Excludes1 note and the excluded code, and look for a provider statement on whether the two conditions are related.

Reason: Excludes1 means the two are not coded together; the exception is when the record shows the conditions are unrelated to each other (Guidelines I.A.12.a).

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Code Overview

Polymyositis, organ involvement unspecified is a billable ICD-10-CM diagnosis code (M33.20).

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 (1)

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 M33.20 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 7 Excludes1 notes across 3 chapters: G72 — Other and unspecified myopathies (via M33.-), L94 — Other localized connective tissue disorders (via M33.-), M60 — Myositis (via M33.-), M60-M63 — Disorders of muscles (M60-M63) (via M33.-), M61 — Calcification and ossification of muscle (via M33.-), M62 — Other disorders of muscle (via M33.-), M63 — Disorders of muscle in diseases classified elsewhere (via M33.-).

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

Referenced by 2 Excludes2 notes across 2 chapters: I77 — Other disorders of arteries and arterioles (via M33.-), J82 — Pulmonary eosinophilia, not elsewhere classified (via M33.-).

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

Referenced by 1 Code First instruction: J84.170 — Interstitial lung disease with progressive fibrotic phenotype in diseases classified elsewhere (via M33.-).

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.

Referenced by 1 Code Also instruction: I27.21 — Secondary pulmonary arterial hypertension (via M33.2.-).

These codes suggest coding this condition alongside when both are present.

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 4 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 3 MS-DRGs: DRG 545 (MDC 08), DRG 546 (MDC 08), DRG 547 (MDC 08).

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

Clinical classification (AHRQ CCSR):MUS024 — Systemic lupus erythematosus and connective tissue disorders (default).

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.

M33.21 — Polymyositis with respiratory involvement, M33.22 — Polymyositis with myopathy, M33.29 — Polymyositis with other organ involvement

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders) for risk-adjusted payment.

M33.00 — Juvenile dermatomyositis, organ involvement unspecified, M33.01 — Juvenile dermatomyositis with respiratory involvement, M33.02 — Juvenile dermatomyositis with myopathy, M33.03 — Juvenile dermatomyositis without myopathy, M33.09 — Juvenile dermatomyositis with other organ involvement, M33.10 — Other dermatomyositis, organ involvement unspecified, M33.11 — Other dermatomyositis with respiratory involvement, M33.12 — Other dermatomyositis with myopathy, M33.13 — Other dermatomyositis without myopathy, M33.19 — Other dermatomyositis with other organ involvement, M33.21 — Polymyositis with respiratory involvement, M33.22 — Polymyositis with myopathy, M33.29 — Polymyositis with other organ involvement, M33.90 — Dermatopolymyositis, unspecified, organ involvement unspecified, M33.91 — Dermatopolymyositis, unspecified with respiratory involvement, M33.92 — Dermatopolymyositis, unspecified with myopathy, M33.93 — Dermatopolymyositis, unspecified without myopathy, M33.99 — Dermatopolymyositis, unspecified with other organ involvement, M34.0 — Progressive systemic sclerosis, M34.1 — CR(E)ST syndrome, +487 more

Related risk categories

These categories interact through CMS's HCC hierarchy — one can suppress the other's risk-adjustment weight when both are present on a claim.

Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Systemic lupus erythematosus and connective tissue disorders).

M33.00 — Juvenile dermatomyositis, organ involvement unspecified, M33.01 — Juvenile dermatomyositis with respiratory involvement, M33.02 — Juvenile dermatomyositis with myopathy, M33.03 — Juvenile dermatomyositis without myopathy, M33.09 — Juvenile dermatomyositis with other organ involvement, M33.10 — Other dermatomyositis, organ involvement unspecified, M33.11 — Other dermatomyositis with respiratory involvement, M33.12 — Other dermatomyositis with myopathy, M33.13 — Other dermatomyositis without myopathy, M33.19 — Other dermatomyositis with other organ involvement, M33.21 — Polymyositis with respiratory involvement, M33.22 — Polymyositis with myopathy, M33.29 — Polymyositis with other organ involvement, M33.90 — Dermatopolymyositis, unspecified, organ involvement unspecified, M33.91 — Dermatopolymyositis, unspecified with respiratory involvement, M33.92 — Dermatopolymyositis, unspecified with myopathy, M33.93 — Dermatopolymyositis, unspecified without myopathy, M33.99 — Dermatopolymyositis, unspecified with other organ involvement, M34.0 — Progressive systemic sclerosis, M34.1 — CR(E)ST syndrome, +72 more

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Thyroid Stimulating Hormone (TSH)

Contextual Map

Every relationship of M33.20 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 M33.20 with these 11 related codes in Claim Check

Hierarchy

Referenced by Excludes1 notes

Referenced by Excludes2 notes

Referenced by Code First instructions

Referenced by Code Also instructions

Clinical classification (CCSR)

Risk adjustment (CMS-HCC)

  • HCC 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders [CMS-HCC]: “Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders — supersedes HCC 94 (Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders)”— CMS-HCC V28 · 2026

MS-DRG Grouper

MDC crossing

  • MDC 08 — Diseases and Disorders of the Musculoskeletal System and Connective Tissue[MDC crossing]: “Diseases and Disorders of the Musculoskeletal System and Connective Tissue — 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. 18,508 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

  • Polymyositis (acute) (chronic) (hemorrhagic)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes (23)

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. "M33.20 — Polymyositis, organ involvement unspecified." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/m33.20-polymyositis-organ-involvement-unspecified

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Polymyositis, organ involvement unspecified

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 M33.20 in its code family, with their registry titles.

View all codes in the M33 family