G11.2

🧬 ICD-10-CM G11.2 — Late-Onset Cerebellar Ataxia

Billable Code Confirmed

ICD-10-CM G11.2 is a valid, billable 4-character diagnosis code. The first three characters (G11) specify hereditary ataxia, and the 4th character (2) specifies the late-onset variant. No additional characters are required.

Non-Billable Parent Codes — Never Submit These

• ❌ G11 — 3-character header — Lacks specificity regarding the age of onset and type of the hereditary ataxia.

Always submit G11.2 (all 4 characters) when late-onset cerebellar ataxia is established by the provider.

Clinical Context: Distinguishing from Unspecified Ataxia

Do not use R27.0 (Ataxia, unspecified) or R26.0 (Ataxic gait) if the patient has a confirmed diagnosis of a late-onset hereditary or spinocerebellar ataxia. R27.0 is merely a symptom code; G11.2 establishes the definitive, degenerative underlying disease and is required for accurate risk adjustment and medical necessity.

Code Classification

ICD-10-CM Diagnosis Code — wRVU, assistant payable, and global period fields are not applicable. See CPT Procedural Crosswalk and ICD-10-PCS Crosswalk sections for associated procedural billing.

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🔍 Code Description

ICD-10-CM G11.2 classifies Late-onset cerebellar ataxia. This covers a group of hereditary, progressive neurodegenerative disorders characterized by ataxia that typically presents in adulthood (usually after age 20).

Pathophysiologically, the condition involves the progressive degeneration of the cerebellum and often the spinal cord connections (spinocerebellar tracts). These disorders are most commonly inherited in an autosomal dominant pattern (e.g., many of the Spinocerebellar Ataxias or SCAs). Symptoms slowly worsen over time and include uncoordinated movements, wide-based staggering gait, dysarthria (slurred speech), and nystagmus.

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🌳 Code Tree / Hierarchy

G11 Hereditary ataxia ❌ Non-billable
│
├── G11.0 Congenital nonprogressive ataxia ✅ Billable
├── G11.1- Early-onset cerebellar ataxia 
├── G11.2 Late-onset cerebellar ataxia ◀ THIS CODE ✅ Billable
├── G11.3 Cerebellar ataxia with defective DNA repair ✅ Billable
├── G11.4 Hereditary spastic paraplegia ✅ Billable
├── G11.8 Other hereditary ataxias ✅ Billable
└── G11.9 Hereditary ataxia, unspecified ✅ Billable

Specificity: Age of Onset

The age of onset is the critical distinguishing factor between the G11.1- subcategory (early-onset, typically before age 20, such as Friedreich’s ataxia) and G11.2 (late-onset, typically manifesting in adulthood).

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✅ Includes

The following specific eponymous syndromes and clinical terms map directly to G11.2 when documented:

• Marie’s ataxia
• Sanger-Brown ataxia
• Adult-onset Spinocerebellar Ataxia (SCA)

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❌ Excludes

Excludes 2 — May Be Coded in Addition if Separately Present

Code	Description	Note
G80.-	Cerebral palsy	Mutually exclusive by clinical definition, but coded via Type 2 Excludes. A patient could theoretically have unrelated CP in addition to later developing late-onset ataxia.
G60.-	Hereditary and idiopathic neuropathy	May be coded simultaneously if the patient has a distinct, separately identifiable peripheral neuropathy.
E70-E88	Metabolic disorders	Can be coded concurrently if a distinct metabolic condition is present.

Symptom Exclusions

According to ICD-10-CM symptom sequencing rules, if G11.2 is coded, you should NOT routinely code R27.0 (Ataxia, unspecified) alongside it unless the R27.0 represents a distinctly different and unrelated coordination issue, which is extremely rare.

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📋 Clinical Overview

Common Diagnoses / Clinical Indications

Patients assigned this code typically present in neurology clinics with a progressive history of:

• Gait Ataxia: Unsteady, wide-based walking with frequent stumbling.
• Limb Dysmetria: Clumsiness in the hands, difficulty with fine motor tasks (e.g., buttoning shirts, writing).
• Dysarthria: Slow, slurred, or scanning speech.
• Oculomotor Abnormalities: Nystagmus or slow saccades.
• Family History: Often a strong family history of similar adult-onset mobility issues (autosomal dominant inheritance).

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💰 HCC Risk Adjustment (CMS-HCC v28)

Field	Detail
CMS-HCC Model Version	v28 (2024-2025 Implementation)
HCC Assignment	✅ Mapped — HCC 72
HCC Category	Spinal Cord Disorders
RAF Impact	Capturing HCC 72 significantly increases the RAF score, reflecting the chronic cost of physical therapy, mobility aids, and specialized neurological care.

Capture Annually

Because degenerative conditions like late-onset cerebellar ataxia never resolve, they must be assessed, documented (MEAT criteria: Monitor, Evaluate, Assess, Treat), and coded at least once per calendar year to maintain accurate risk adjustment.

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🏥 DRG Assignment

MDC 01 — Diseases and Disorders of the Nervous System

DRG	Title	Est. Relative Weight*
DRG 058	Multiple Sclerosis and Cerebellar Ataxia with MCC	~2.05
DRG 059	Multiple Sclerosis and Cerebellar Ataxia with CC	~1.15
DRG 060	Multiple Sclerosis and Cerebellar Ataxia without CC/MCC	~0.85

Approximate. Verify against IPPS FY2026 Final Rule tables.

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🛠️ Commonly Associated CPT Codes (Neurology / Outpatient)

Procedure and E/M Context

Management of late-onset ataxia involves extensive diagnostic workups (to rule out acquired causes like stroke, tumor, or toxicity) and ongoing evaluation and management.

CPT Code	Description	Modifier Notes / wRVU
99205	Office or other outpatient visit for the evaluation and management of a new patient (High MDM, or 60-74 mins)	Often used for the initial, highly complex neurogenetics evaluation. (wRVU: 3.16 · Global: XXX · Assistant: ❌)
99214	Office or other outpatient visit for an established patient (Moderate MDM)	Used for routine progressive monitoring and care coordination. (wRVU: 1.92 · Global: XXX · Assistant: ❌)
70551	Magnetic resonance (e.g., proton) imaging, brain; without contrast material	Billed with Modifier -26 by the interpreting physician. Crucial to evaluate for cerebellar and brainstem atrophy and rule out acquired causes. (wRVU: ~1.48 · Global: XXX · Assistant: ❌)
81404 / 81405	Molecular pathology procedures (Tier 2)	Genetic testing codes often used to test for specific Spinocerebellar Ataxia (SCA) repeat expansions. NCCI: Cannot typically bundle multiple Tier 2 tests for the same gene.

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💊 Coding Scenarios and Examples

Scenario 1 — Outpatient Neurology Visit (Established)

Clinical Vignette: A 45-year-old male with a known diagnosis of Spinocerebellar Ataxia Type 3 (Machado-Joseph disease) presents for a 6-month follow-up. The neurologist notes worsening gait instability and prescribes physical therapy for fall prevention, as well as a rolling walker. The visit involved moderate medical decision-making.

Diagnoses:

• G11.2 — Late-onset cerebellar ataxia (Primary reason for the visit)
• Z99.3 — Dependence on wheelchair (if applicable, though in this case a walker is prescribed, so Z46.1 Encounter for fitting and adjustment of hearing aid/walker etc. could be used as supplementary).

Procedure:

• 99214 — E/M established patient, Moderate MDM

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Scenario 2 — Overcoming Symptom Coding

Clinical Vignette: A primary care provider’s referral reads: “Please evaluate patient for R27.0 (Ataxia).” The consulting neurologist performs a comprehensive exam, reviews a positive genetic test for an SCA mutation, and documents: “The patient’s ataxia is secondary to late-onset Spinocerebellar Ataxia.”

Corrected ICD-10-CM Coding:

• G11.2 — Late-onset cerebellar ataxia
• Do not bill R27.0. The definitive diagnosis of late-onset cerebellar ataxia replaces the symptom code.

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⚠️ Coding Pitfalls and Tips

	Pitfall or Tip
❌	Defaulting to R27.0. Using R27.0 (Unspecified ataxia) when a specific diagnosis of hereditary, late-onset, or spinocerebellar ataxia is documented results in a loss of specificity and misses out on critical HCC risk adjustment data.^3
❌	Ignoring Age of Onset. Do not use G11.2 for a child or a patient whose symptoms clearly began in adolescence. Review the chart for Friedreich’s ataxia or early-onset variants (G11.1-).
✅	Query for SCA Type vs. General Ataxia. If the provider documents “SCA” (Spinocerebellar Ataxia), it natively codes to G11.2 if it is late-onset. Ensure the provider clearly documents the onset timeframe to justify the code selection.
✅	Capture Annually for HCC. Although there is no cure, the active management of symptoms, mobility device coordination, and physical therapy referrals satisfy the MEAT criteria to report this code annually for Medicare Advantage patients.

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📚 Sources

1. CMS/NCHS. ICD-10-CM Official Guidelines for Coding and Reporting, FY2025/FY2026. Section I.B.4: Signs and Symptoms. 2. American Academy of Neurology (AAN). Practice Parameter: Evaluation of the adult with suspected cerebellar ataxia. 3. CMS. 2025-2026 Medicare Advantage Risk Adjustment — CMS-HCC Model v28 ICD-10-CM Mappings. 4. American Medical Association (AMA). CPT Professional Edition 2025. Evaluation and Management Guidelines. 5. CMS. IPPS Final Rule FY2026 — MS-DRG Definitions Manual v43.