A81.1
BillableSubacute sclerosing panencephalitis
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is A81.1 an HCC code?
Yes. A81.1 maps to Dementia, Mild or Unspecified under the CMS-HCC V28 risk adjustment model.
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 A81.1
For A81.1 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 A81.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
A81.1 is the ICD-10-CM diagnosis code for subacute sclerosing panencephalitis. A rare, progressive brain infection caused by the measles virus that develops years after the initial measles infection, leading to inflammation and degeneration of brain tissue. This condition is fatal and causes progressive neurological decline including personality changes, memory loss, and loss of motor control. A81.1 sits in the ICD-10-CM chapter for certain infectious and parasitic diseases (a00-b99), within the section covering viral and prion infections of the central nervous system (a80-a89).
Under the CMS-HCC V28 risk adjustment model, A81.1 maps to Dementia, Mild or Unspecified (HCC 127) with a community, non-dual, aged base RAF weight of 0.464. A81.1 was not retained as a payment HCC under the older V24 model, so V28 introduced or recategorized it during the 2024–2026 phase-in. 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 code requires documentation of the confirmed diagnosis of SSPE; do not code based on suspected or possible cases without definitive confirmation. Because A81.1 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 A81.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code requires documentation of the confirmed diagnosis of SSPE; do not code based on suspected or possible cases without definitive confirmation
- •SSPE is typically a late complication of measles infection, so consider coding both the current SSPE diagnosis (A81.1) and any relevant history of measles if documented in the medical record
Clinical Significance
Subacute sclerosing panencephalitis is a rare, progressive, and invariably fatal brain disease caused by a defective measles virus that persists in the central nervous system years after the initial measles infection. It typically presents 7-10 years after measles infection and is a compelling argument for measles vaccination.
Documentation Requirements
- ✓Confirmed SSPE diagnosis with elevated measles antibody titers in cerebrospinal fluid
- ✓History of measles infection (including approximate age at infection)
- ✓EEG findings showing characteristic periodic complexes (Radermecker complexes)
- ✓Clinical stage documented (Jabbour staging: I through IV)
- ✓Neurological examination findings: cognitive decline, myoclonus, motor deterioration