What is ICD-10 code G13.2?

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 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. G13.2 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. G13.2 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. G13.2 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for G13.2?

G13.2 does not map to a payment HCC under either the CMS-HCC V28 risk adjustment model or the older V24 model. V28 reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. Because neither model rewards G13.2 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a payment HCC.

What should coders know when reporting G13.2?

Ensure myxedema is documented in the medical record before assigning this code Code the underlying thyroid condition separately if applicable

G13.2: Systemic atrophy primarily affecting the central nervous system in myxedema — ICD-10

ICD-10-CM Code View

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Code lookupG13.2Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the nervous system (G00-G99) / Systemic atrophies primarily affecting the central nervous system (G10-G14)

G13.2

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

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.

Buddy Insight

Systemic atrophy primarily affecting the central nervous system in myxedema represents neurological degeneration caused by severe untreated hypothyroidism.

CMS-HCC V28

Not risk-adjusted for this model/period.

RAF 0

CMS-HCC V24

Not risk-adjusted for this model/period.

RAF 0

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Not risk-adjusted for this model/period.

RAF 0

RXHCC

Mapped

HCC 112

Dementia and Other Specified ...

RAF 0.0

Code Trumping

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Code Book Path

Official

G13Systemic atrophies primarily affecting central nervous system in diseases classified elsewhere

G13.2Systemic atrophy primarily affecting the central nervous system in myxedema

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for G13.2 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for G13.2 in this effective period.

Related Child Codes

Official

G13.0Paraneoplastic neuromyopathy and neuropathy

G13.1Other systemic atrophy primarily affecting central nervous system in neoplastic disease

G13.8Systemic atrophy primarily affecting central nervous system in other diseases classified elsewhere

Includes

Official

ICD-10-CM does not list Includes notes for G13.2 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for G13.2 in this effective period.

Code First

Official

underlying disease, such as:
hypothyroidism (E03.-)
myxedematous congenital iodine deficiency (E00.1)

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for G13.2 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for G13.2 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

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

MEAT Support

HCC Buddy guidance

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

Audit Caution

HCC Buddy guidance

Failing to code the underlying thyroid condition separately

Using generic neurodegeneration codes when myxedema-related etiology is documented

Confusing myxedema coma (acute) with chronic neurological degeneration from myxedema

Not documenting the causal relationship between hypothyroidism and neurological decline

Common Mistakes

HCC Buddy guidance

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

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

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

RxHCCHCC 112, Dementia and Other Specified Brain Disorders

0.000

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.

Work G13.2 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

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.

Coder workflow notes

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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

underlying disease, such as:
hypothyroidism (E03.-)
myxedematous congenital iodine deficiency (E00.1)

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