G12.21 ICD-10-CM Code: Amyotrophic lateral sclerosis
G12.21 maps to CMS-HCC V28 190. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools
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FY 2026 Apr update / Diseases of the nervous system (G00-G99) / Systemic atrophies primarily affecting the central nervous system (G10-G14)
G12.21
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceAmyotrophic lateral sclerosis
Amyotrophic lateral sclerosis (ALS) is a progressive neurological disease that causes muscle weakness and paralysis by damaging nerve cells that control voluntary muscles. This condition gradually worsens over time and affects a person's ability to move, speak, eat, and breathe.
Buddy Insight
Amyotrophic lateral sclerosis is one of the most devastating neurodegenerative diseases, causing progressive paralysis and death typically within 3-5 years of diagnosis.
CMS-HCC V28
MappedHCC 190
Coefficient HCC 190: 1.175 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
Context neededHCC 111
Coefficient needs member context
ESRD/PACE
Context neededHCC 73
Coefficient needs member context
RXHCC
Context neededHCC 154
Coefficient needs member context
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for G12.21. 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
- certain infectious and parasitic diseases (A00-B99)Inherited from G00-G99
- complications of pregnancy, childbirth and the puerperium (O00-O9A)Inherited from G00-G99
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)Inherited from G00-G99
- endocrine, nutritional and metabolic diseases (E00-E88)Inherited from G00-G99
- injury, poisoning and certain other consequences of external causes (S00-T88)Inherited from G00-G99
- neoplasms (C00-D49)Inherited from G00-G99
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)Inherited from G00-G99
Related Codes
Includes
OfficialNo Includes notes are included in this display for G12.21. Check the code and parent instructions in the Code Book.
Excludes 1
OfficialNo Excludes 1 notes are included in this display for G12.21. Check the code and parent instructions in the Code Book.
Code First
OfficialNo Code First sequencing instructions are included in this display for G12.21. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for G12.21. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for G12.21. 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 G12.21 an HCC code?
Yes. G12.21 (Amyotrophic lateral sclerosis) maps to HCC 190, Amyotrophic Lateral Sclerosis and Other Motor Neuron Disease, Spinal Muscular Atrophy under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 1.175. 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: G12.21 is billable and maps to V28 HCC 190, Amyotrophic Lateral Sclerosis and Other Motor Neuron Disease, Spinal Muscular Atrophy. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- G12.21
- Description
- Amyotrophic lateral sclerosis
- HCC (V28)
- HCC 190 — Amyotrophic Lateral Sclerosis and Other Motor Neuron Disease, Spinal Muscular Atrophy
- RAF reference coefficient
- 1.175
- 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 G12.21 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for G12.21
For G12.21, 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
G12.21 is the ICD-10-CM diagnosis code for amyotrophic lateral sclerosis. Amyotrophic lateral sclerosis (ALS) is a progressive neurological disease that causes muscle weakness and paralysis by damaging nerve cells that control voluntary muscles. This condition gradually worsens over time and affects a person's ability to move, speak, eat, and breathe. G12.21 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).
Under the CMS-HCC V28 risk adjustment model, G12.21 maps to Amyotrophic Lateral Sclerosis and Other Motor Neuron Disease, Spinal Muscular Atrophy (HCC 190) with a source-labeled community, non-dual, aged reference coefficient of 1.175. 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.
ALS is a chronic progressive condition; ensure documentation clearly supports the diagnosis and specify the stage or severity if documented (onset, progression, affected body regions). For G12.21, 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 G12.21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •ALS is a chronic progressive condition; ensure documentation clearly supports the diagnosis and specify the stage or severity if documented (onset, progression, affected body regions)
- •Code G12.21 is specific to ALS; do not confuse with other motor neuron diseases coded under G12.2x (such as progressive muscular atrophy G12.25 or primary lateral sclerosis G12.29)
Clinical Significance
Amyotrophic lateral sclerosis is one of the most devastating neurodegenerative diseases, causing progressive paralysis and death typically within 3-5 years of diagnosis. It involves both upper and lower motor neuron degeneration and drives extremely high healthcare costs including ventilator support, feeding tubes, communication devices, and expensive medications like riluzole and edaravone.
Documentation Requirements
- ✓El Escorial criteria or equivalent diagnostic criteria documented
- ✓Both upper motor neuron signs (spasticity, hyperreflexia) and lower motor neuron signs (atrophy, fasciculations) present
- ✓Electromyography findings consistent with widespread denervation
- ✓Rate of disease progression and affected body regions
- ✓Current respiratory function (forced vital capacity)
- ✓Treatment with disease-modifying medications (riluzole, edaravone, tofersen) if applicable
Commonly Confused Codes
- •G12.23: Primary lateral sclerosis: upper motor neuron only, slower progression, better prognosis
- •G12.25: Progressive spinal muscle atrophy: lower motor neuron only
- •G12.22: Progressive bulbar palsy: bulbar-onset motor neuron disease
- •G12.20: Motor neuron disease, unspecified: do not use when amyotrophic lateral sclerosis is diagnosed