G12.21
BillableAmyotrophic lateral sclerosis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G12.21 an HCC code?
Yes. G12.21 maps to Motor Neuron Disease, Including Amyotrophic Lateral Sclerosis under the CMS-HCC V28 risk adjustment model (and Amyotrophic Lateral Sclerosis and Other Motor Neuron Disease 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 G12.21
For G12.21 to 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 G12.21 during that encounter — not just copy-forwarded from a problem list.
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 Motor Neuron Disease, Including Amyotrophic Lateral Sclerosis (HCC 190) with a community, non-dual, aged base RAF weight of 0.935. Under the older CMS-HCC V24 model, G12.21 maps to Amyotrophic Lateral Sclerosis and Other Motor Neuron Disease (HCC 73) with a community, non-dual, aged base RAF weight of 0.896. 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.
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). Because G12.21 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 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