ICD-10 M33.21
Billable / Specific HCC v28: 112 CCPolymyositis with respiratory involvement
About ICD-10-CM M33.21
ICD-10-CM code M33.21 represents Polymyositis with respiratory involvement. This is a billable/specific code in the Musculoskeletal and Connective Tissue chapter (block M33). The 2026 edition of ICD-10-CM M33.21 became effective on October 1, 2025.
Coding Tips for M33.21
Specialist guidance from the PayerReady Medical Coding Team. Specificity warnings, HCC capture rules, sequencing notes.
M33.21 is a CMS-HCC v28 risk-adjustment code (category 112). To count for the patient Risk Adjustment Factor (RAF), document the diagnosis with MEAT language each calendar year: Monitored, Evaluated, Assessed, Treated. A diagnosis on the problem list alone does not satisfy CMS RADV audit standards. Include the diagnosis in the assessment with current status and current treatment plan.
M33.21 is designated CC for MS-DRG grouping. On inpatient claims, this code can shift the DRG to the with-CC variant when documented as a present-on-admission secondary diagnosis. Hospital CDI programs flag CC opportunities during chart review. Failure to capture this code may leave 30 to 80 percent of the inpatient stay revenue unrealized.
Medicare Advantage HCC Impact
Capture this diagnosis annually for accurate risk adjustment. Missed HCC captures are the #1 revenue leak in Medicare Advantage risk programs.
Inpatient DRG Impact, CC
codes Polymyositis with respiratory involvement. As a Complication/Comorbidity (CC), this contributes to DRG severity adjustment when documented alongside the principal diagnosis.
Medicare LCD Coverage for M33.21
Local Coverage Determinations (LCDs) from CMS MACs that list M33.21 as a covered diagnosis.
Showing top 10 of 377 total . Click a CPT for full coverage scope.
Commercial Payer Coverage
Coverage policies from major commercial payers referencing M33.21.
1 Cigna
5 Medicare
CPT Codes Commonly Billed with M33.21
Procedures frequently paired with this diagnosis based on PayerReady's Dx↔Px linkage data.
We don't have CPT pairings indexed for this specific code yet. Use the CPT search above to find common procedures, or check your payer's published medical policy for code-specific guidance.
Convert M33.21 to ICD-9-CM
Per CMS General Equivalence Mappings (GEMs), useful for legacy data review and historical claim analysis.
| ICD-10 | ICD-9 | Mapping Flags |
|---|---|---|
| M33.21 | 5178 | 10112 |
| M33.21 | 7104 | 10111 |
Flags format (5 digits): Approximate · No Map · Combination · Scenario · Choice List. Source: CMS 2017 GEMs (final version).
Codes Adjacent To M33.21
Other codes in section M30-M36 (Systemic connective tissue disorders).
ICD-10 M33.21, Billing FAQ
Is ICD-10 code M33.21 billable? +
Yes, M33.21 is a billable ICD-10-CM code that can appear as a primary or secondary diagnosis on claims.
Does M33.21 affect Medicare Advantage HCC risk adjustment? +
Yes. M33.21 maps to CMS-HCC v28 category 112. Capture this diagnosis annually for accurate Medicare Advantage risk score.
Is M33.21 a CC or MCC for inpatient DRG? +
Yes, this code is designated as CC. Documenting as a secondary diagnosis on inpatient claims can shift the DRG to a higher-weighted category.
What ICD-9 codes does M33.21 map to? +
Per CMS GEMs, M33.21 maps to ICD-9 codes: 5178, 7104. Useful for legacy data review and historical claim analysis.
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Reviewed by the PayerReady Medical Coding Team
Verified against the CMS 2026 code set on May 31, 2026.
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