G23.1
BillableProgressive supranuclear ophthalmoplegia [Steele-Richardson-Olszewski]
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is G23.1 an HCC code?
Yes. G23.1 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 G23.1
For G23.1to 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 G23.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
G23.1 is the ICD-10-CM diagnosis code for progressive supranuclear ophthalmoplegia [steele-richardson-olszewski]. A rare progressive neurological disorder affecting eye movement and muscle control, characterized by difficulty moving the eyes downward and progressive movement problems. G23.1 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, G23.1 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, G23.1 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 also known as Steele-Richardson-Olszewski syndrome; document the specific clinical presentation including eye movement difficulties. Because G23.1 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 G23.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is also known as Steele-Richardson-Olszewski syndrome; document the specific clinical presentation including eye movement difficulties
- •Verify documentation of progressive symptoms and neuroimaging findings to support this diagnosis
Clinical Significance
Progressive supranuclear palsy (Steele-Richardson-Olszewski syndrome) is a tauopathy causing progressive gaze palsy (especially downward gaze), postural instability with early falls, axial rigidity, and cognitive decline. It is commonly misdiagnosed as Parkinson's disease but has a faster course and poor levodopa response, making accurate coding essential for care planning.
Documentation Requirements
- ✓Vertical gaze palsy, especially impaired downward gaze, documented on examination
- ✓Early postural instability with falls (typically within first year of onset)
- ✓Axial rigidity greater than appendicular rigidity
- ✓Poor or absent response to levodopa trial
- ✓Progressive cognitive decline or behavioral changes
- ✓Brain MRI showing midbrain atrophy ('hummingbird sign' or 'morning glory sign') if available
Commonly Confused Codes
- •G20.A1-G20.C — Parkinson's disease: the most common misdiagnosis; progressive supranuclear palsy has early falls, gaze palsy, and poor levodopa response
- •G23.2 — Striatonigral degeneration: another atypical parkinsonian syndrome but with cerebellar features
- •G90.3 — Multi-system degeneration: for multisystem atrophy which has autonomic dysfunction
- •G23.0 — Hallervorden-Spatz disease: different mechanism with brain iron accumulation