G71.21 ICD-10-CM Code: Nemaline myopathy
G71.21 maps to CMS-HCC V28 197. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · free HCC coding tools
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FY 2026 Apr update / Diseases of the nervous system (G00-G99) / Diseases of myoneural junction and muscle (G70-G73)
G71.21
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceNemaline myopathy
A rare inherited muscle disease present from birth characterized by rod-like structures visible under the microscope in muscle fibers, causing weakness.
Buddy Insight
Nemaline myopathy is a congenital muscle disease characterized by rod-shaped inclusions (nemaline bodies) in muscle fibers, causing variable degrees of weakness from severe neonatal to mild adult-onset forms.
CMS-HCC V28
MappedHCC 197
Coefficient HCC 197: 0.426 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 117
Code-level coefficient reference
ESRD/PACE
MappedHCC 76
Code-level coefficient reference
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for G71.21. Check the code and parent instructions in the Code Book.
Excludes 2
Official- certain conditions originating in the perinatal period (P04-P96)Inherited from G00-G99, G71, G71.2
- certain infectious and parasitic diseases (A00-B99)Inherited from G00-G99, G71, G71.2
- complications of pregnancy, childbirth and the puerperium (O00-O9A)Inherited from G00-G99, G71, G71.2
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)Inherited from G00-G99, G71, G71.2
- endocrine, nutritional and metabolic diseases (E00-E88)Inherited from G00-G99, G71, G71.2
- injury, poisoning and certain other consequences of external causes (S00-T88)Inherited from G00-G99, G71, G71.2
- neoplasms (C00-D49)Inherited from G00-G99, G71, G71.2
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)Inherited from G00-G99, G71, G71.2
- arthrogryposis multiplex congenita (Q74.3)Inherited from G00-G99, G71, G71.2
- metabolic disorders (E70-E88)Inherited from G00-G99, G71, G71.2
- myositis (M60.-)Inherited from G00-G99, G71, G71.2
Related Codes
Includes
OfficialNo Includes notes are included in this display for G71.21. Check the code and parent instructions in the Code Book.
Excludes 1
OfficialNo Excludes 1 notes are included in this display for G71.21. Check the code and parent instructions in the Code Book.
Code First
OfficialNo Code First sequencing instructions are included in this display for G71.21. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for G71.21. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for G71.21. Check the code and parent instructions in the Code Book.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is G71.21 an HCC code?
Yes. G71.21 (Nemaline myopathy) maps to HCC 197, Muscular Dystrophy under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.426. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: G71.21 is billable and maps to V28 HCC 197, Muscular Dystrophy. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- G71.21
- Description
- Nemaline myopathy
- HCC (V28)
- HCC 197 — Muscular Dystrophy
- RAF reference coefficient
- 0.426
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work G71.21 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for G71.21
For G71.21, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Coder workflow notes
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What This Code Means
G71.21 is the ICD-10-CM diagnosis code for nemaline myopathy. A rare inherited muscle disease present from birth characterized by rod-like structures visible under the microscope in muscle fibers, causing weakness. G71.21 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering diseases of myoneural junction and muscle (g70-g73).
Under the CMS-HCC V28 risk adjustment model, G71.21 maps to Muscular Dystrophy (HCC 197) with a source-labeled community, non-dual, aged reference coefficient of 0.426. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
Nemaline myopathy diagnosis typically requires muscle biopsy showing characteristic nemaline rods. For G71.21, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for G71.21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Nemaline myopathy diagnosis typically requires muscle biopsy showing characteristic nemaline rods
- •Document the severity and distribution of muscle weakness, as this affects functional status and treatment planning
Clinical Significance
Nemaline myopathy is a congenital muscle disease characterized by rod-shaped inclusions (nemaline bodies) in muscle fibers, causing variable degrees of weakness from severe neonatal to mild adult-onset forms. Severe forms can cause respiratory failure and feeding difficulties. Accurate coding reflects the lifelong care complexity and supports appropriate resource allocation for these patients.
Documentation Requirements
- ✓Muscle biopsy showing characteristic nemaline rods (rod bodies) on Gomori trichrome staining
- ✓Genetic testing identifying mutations in nemaline myopathy genes (NEB, ACTA1, TPM2, TPM3, etc.) when available
- ✓Clinical severity classification: severe neonatal, intermediate, typical, mild
- ✓Respiratory function assessment and ventilatory support needs
- ✓Feeding and swallowing evaluation
- ✓Provider's explicit diagnosis of nemaline myopathy
Commonly Confused Codes
- •G71.20: Congenital myopathy, unspecified should not be used when nemaline bodies are confirmed on biopsy
- •G71.220: X-linked myotubular myopathy has centrally placed nuclei, not nemaline rods, on biopsy
- •G71.29: Other congenital myopathy is for non-nemaline structural myopathies
- •G71.228: Other centronuclear myopathy involves central nuclei, not rod bodies