G71.21
BillableNemaline myopathy
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G71.21 an HCC code?
Yes. G71.21 maps to Muscular Dystrophy under the CMS-HCC V28 risk adjustment model (and Muscular Dystrophy under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for G71.21
For G71.21to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- 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
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed G71.21 during that encounter — not just copy-forwarded from a problem list.
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 community, non-dual, aged base RAF weight of 0.000. Under the older V24 model, G71.21 mapped to the same category but with a base RAF weight of 0.358 — V28 recalibrated weights across the entire model. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
Nemaline myopathy diagnosis typically requires muscle biopsy showing characteristic nemaline rods. Because G71.21 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. 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, RAF weights, 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