G23.0
BillableHallervorden-Spatz disease
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G23.0 an HCC code?
Yes. G23.0 maps to Parkinson and Huntington Diseases under the CMS-HCC V28 risk adjustment model (and Parkinson's and Huntington's Diseases 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 G23.0
For G23.0to 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 G23.0 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G23.0 is the ICD-10-CM diagnosis code for hallervorden-spatz disease. A rare inherited neurological disorder characterized by progressive movement problems, including parkinsonism, dystonia, and spasticity, typically beginning in childhood or early adulthood. G23.0 sits in the ICD-10-CM chapter for diseases of the nervous system (g00-g99), within the section covering extrapyramidal and movement disorders (g20-g26).
Under the CMS-HCC V28 risk adjustment model, G23.0 maps to Parkinson and Huntington Diseases (HCC 199) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, G23.0 maps to Parkinson's and Huntington's Diseases (HCC 78) with a community, non-dual, aged base RAF weight of 0.584. 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.
This is a rare genetic disorder; ensure documentation supports the diagnosis with clinical findings and family history when available. Because G23.0 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 G23.0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a rare genetic disorder; ensure documentation supports the diagnosis with clinical findings and family history when available
- •Consider coding associated symptoms such as dementia or psychiatric manifestations if present
Clinical Significance
Hallervorden-Spatz disease (now known as pantothenate kinase-associated neurodegeneration or PKAN) is a rare genetic neurodegenerative disorder characterized by iron accumulation in the brain's basal ganglia. It causes progressive dystonia, parkinsonism, spasticity, and cognitive decline, typically beginning in childhood and requiring lifelong complex neurological care.
Documentation Requirements
- ✓Brain MRI showing 'eye of the tiger' sign on T2-weighted images (characteristic iron deposits in globus pallidus)
- ✓Genetic testing for PANK2 gene mutations if available
- ✓Progressive dystonia and/or parkinsonism documented on neurological examination
- ✓Age of onset (classic form in first decade, atypical form later)
- ✓Family history consistent with autosomal recessive inheritance
- ✓Associated symptoms documented (retinal degeneration, psychiatric symptoms, dementia)
Commonly Confused Codes
- •G24.1 — Genetic torsion dystonia: can present similarly but lacks brain iron accumulation
- •G20.A1-G20.C — Parkinson's disease: idiopathic, not associated with brain iron deposition
- •G23.1 — Progressive supranuclear ophthalmoplegia: different neurodegenerative process affecting eye movements
- •G23.2 — Striatonigral degeneration: different basal ganglia degeneration without iron accumulation pattern