G04.90 — Encephalitis and encephalomyelitis, unspecified
G04.90 is a billable, specific ICD-10-CM code for encephalitis and encephalomyelitis, unspecified. It is valid for submission on a claim.
Inclusion terms
Alternative wordings a physician may use in the chart for this same code.
- Ventriculitis (cerebral) NOS
Excludes1 inherited from the categories above G04.90
These are not written on G04.90, but they bind it: a note on a category applies to every code beneath it. Billing G04.90 with anything listed here is a denial.
Excludes2 inherited from the categories above G04.90
Also inherited, and the opposite of Excludes1: these conditions are not part of G04.90, but a patient can have both, so you may code both.
Other codes that can never be billed with G04.90
These codes carry an Excludes1 note pointing at G04.90. The conflict binds both ways, but ICD-10-CM only writes it down on one side — so you would not find this by reading G04.90 alone.
- G03Meningitis due to other and unspecified causes
Risk adjustment
G04.90 does not map to an HCC and does not risk-adjust under CMS-HCC V28. That is normal — most ICD-10 codes do not. It still needs to be coded correctly; it just will not move a RAF score.
Medicare coverage
G04.90 is named in 15 Medicare coverage policies — 15 listing it as supporting medical necessity. Which of them applies to you depends on your Medicare contractor, and coverage genuinely differs by state.
- A56551Billing and Coding: Visual Fields Testing
- A56619Billing and Coding: Nerve Conduction Studies and Electromyography
- A56695Billing and Coding: Implantable Infusion Pump
- A56771Billing and Coding: Special Electroencephalography
How G04.90 is indexed
Coders do not find codes by browsing the tabular list — they look them up in the alphabetic index, under the word the physician wrote. These are the index entries that lead here, so you can see which chart wordings map to G04.90.
- Encephalitis(chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
- Encephalomyelitis
- Hematomyelitis
- Meningoencephalitis
- Ventriculitis(cerebral)
- Infection, infected, infective›brain
Code history
G04.90 has not changed since FY2024 — no addition, revision or deletion across the three most recent ICD-10-CM releases.
Related codes at this level
Codes that share G04.9. If G04.90 is not quite right, the correct code is usually one of these.
Questions about G04.90
- Is G04.90 a billable ICD-10-CM code?
- Yes. G04.90 is a billable, specific ICD-10-CM code and is valid for submission on a claim.
- Where does G04.90 sit in the tabular list?
- Diseases of the nervous system (G00-G99), in the block Inflammatory diseases of the central nervous system (G00-G09).
- What cannot be coded together with G04.90?
- G04.90 carries Excludes1 notes, which means the conditions they list can never be coded together with it on the same encounter. Some are written on the categories above G04.90 (G04) and apply to it just the same.