G13.2
BillableSystemic atrophy primarily affecting the central nervous system in myxedema
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G13.2 an HCC code?
No. G13.2 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
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 G13.2
For G13.2to 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 G13.2 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G13.2 is the ICD-10-CM diagnosis code for systemic atrophy primarily affecting the central nervous system in myxedema. Wasting and degeneration of the brain and spinal cord caused by myxedema, a severe form of hypothyroidism with accumulation of mucopolysaccharides in tissues. G13.2 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering systemic atrophies primarily affecting the central nervous system (g10-g14).
G13.2 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.
G13.2 does not map to any V28 or V24 HCC. It maps only to RxHCC 112 (Fibrosis of Lung and Other Chronic Lung Disorders) with 0.0 RAF weight. This code has minimal direct risk adjustment impact; the underlying thyroid condition may provide additional value.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for G13.2 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Ensure myxedema is documented in the medical record before assigning this code
- •Code the underlying thyroid condition separately if applicable
Clinical Significance
Systemic atrophy primarily affecting the central nervous system in myxedema represents neurological degeneration caused by severe untreated hypothyroidism. This diagnosis highlights the critical importance of thyroid function management and signals that neurological damage may be irreversible, requiring ongoing neurological and endocrine care coordination.
Documentation Requirements
- ✓Documented myxedema (severe hypothyroidism with mucinous tissue changes)
- ✓Thyroid function test results confirming severe hypothyroidism
- ✓Neurological examination documenting central nervous system dysfunction
- ✓Brain imaging showing atrophy or white matter changes if available
- ✓Duration of untreated or undertreated hypothyroidism
- ✓Underlying thyroid condition coded separately
Code First
Commonly Confused Codes
- •E03.9 — Hypothyroidism, unspecified: captures the thyroid condition but not the neurological complication
- •G13.8 — Systemic atrophy in other diseases classified elsewhere: for non-myxedema causes
- •G31.9 — Degenerative disease of nervous system, unspecified: does not capture the myxedema etiology
- •E03.5 — Myxedema coma: an acute emergency, while G13.2 represents chronic neurological sequelae