ICD-10 Code for Encephalitis

The default ICD-10-CM 2027 code for encephalitis (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute) is G04.90 – Encephalitis and encephalomyelitis, unspecified. More specific codes depend on the details documented, as listed in the official index (65 codes, 64 billable).

Main code: G04.90 – Encephalitis and encephalomyelitis, unspecified
Billable: Yes

Index entries for Encephalitis

acute – A86 – see also Encephalitis, viral
- disseminated – G04.00
  - infectious – G04.01
  - noninfectious – G04.81
  - postimmunization (postvaccination) – G04.02
  - postinfectious – G04.01
- inclusion body – A85.8
- necrotizing hemorrhagic – G04.30
  - postimmunization – G04.32
  - postinfectious – G04.31
  - specified NEC – G04.39
arboviral, arbovirus NEC – A85.2
arthropod-borne NEC (viral) – A85.2
Australian – A83.4
California (virus) – A83.5
Central European (tick-borne) – A84.1
Czechoslovakian – A84.1
Dawson's (inclusion body) – A81.1
diffuse sclerosing – A81.1
disseminated, acute – G04.00
due to
- cat scratch disease – A28.1
- human immunodeficiency virus (HIV) – B20 – G05.3 [manifestation]
- malaria – see Malaria
- rickettsiosis – see Rickettsiosis
- smallpox inoculation – G04.02
- typhus – see Typhus
Eastern equine – A83.2
endemic (viral) – A86
epidemic NEC (viral) – A86
equine (acute) (infectious) (viral) – A83.9
- Eastern – A83.2
- Venezuelan – A92.2
- Western – A83.1
Far Eastern (tick-borne) – A84.0
following vaccination or other immunization procedure – G04.02
herpes zoster – B02.0
herpesviral – B00.4
- due to herpesvirus 6 – B10.01
- due to herpesvirus 7 – B10.09
- specified NEC – B10.09
Ilheus (virus) – A83.8
inclusion body – A81.1
in (due to)
- actinomycosis – A42.82
- adenovirus – A85.1
- African trypanosomiasis – B56.9 – G05.3 [manifestation]
- Chagas' disease (chronic) – B57.42
- cytomegalovirus – B25.8
- enterovirus – A85.0
- herpes (simplex) – B00.4
  - due to herpesvirus 6 – B10.01
  - due to herpesvirus 7 – B10.09
  - specified NEC – B10.09
- infectious disease NEC – B99 (header) – G05.3 [manifestation]
- influenza – see Influenza, with, encephalopathy
- listeriosis – A32.12
- measles – B05.0
- mumps – B26.2
- naegleriasis – B60.2
- parasitic disease NEC – B89 – G05.3 [manifestation]
- poliovirus – A80.9 – G05.3 [manifestation]
- rubella – B06.01
- syphilis
  - congenital – A50.42
  - late – A52.14
- systemic lupus erythematosus – M32.19 – G05.3 [manifestation]
- toxoplasmosis (acquired) – B58.2
  - congenital – P37.1
- tuberculosis – A17.82
- zoster – B02.0
infectious (acute) (virus) – A86
Japanese (B type) – A83.0
La Crosse – A83.5
lead – see Poisoning, lead
lethargica (acute) (infectious) – A85.8
louping ill – A84.89
lupus erythematosus, systemic – M32.19 – G05.3 [manifestation]
lymphatica – A87.2
Mengo – A85.8
meningococcal – A39.81
Murray Valley – A83.4
otitic NEC – H66.40 – G05.3 [manifestation]
parasitic NOS – B71.9
periaxial – G37.0
periaxialis (concentrica) (diffuse) – G37.5
postchickenpox – B01.11
postexanthematous NEC – B09
postimmunization – G04.02
postinfectious NEC – G04.01
postmeasles – B05.0
postvaccinal – G04.02
postvaricella – B01.11
postviral NEC – A86
Powassan – A84.81
Rasmussen – G04.81
Rio Bravo – A85.8
Russian
- autumnal – A83.0
- spring-summer (taiga) – A84.0
saturnine – see Poisoning, lead
specified NEC – G04.81
St. Louis – A83.3
subacute sclerosing – A81.1
summer – A83.0
suppurative – G04.81
tick-borne – A84.9
Torula, torular (cryptococcal) – B45.1
toxic NEC – G92.8
trichinosis – B75 – G05.3 [manifestation]
type
- B – A83.0
- C – A83.3
van Bogaert's – A81.1
Venezuelan equine – A92.2
Vienna – A85.8
viral, virus – A86
- arthropod-borne NEC – A85.2
  - mosquito-borne – A83.9
    - Australian X disease – A83.4
    - California virus – A83.5
    - Eastern equine – A83.2
    - Japanese (B type) – A83.0
    - Murray Valley – A83.4
    - specified NEC – A83.8
    - St. Louis – A83.3
    - type B – A83.0
    - type C – A83.3
    - Western equine – A83.1
  - tick-borne – A84.9
    - biundulant – A84.1
    - central European – A84.1
    - Czechoslovakian – A84.1
    - diphasic meningoencephalitis – A84.1
    - Far Eastern – A84.0
    - Russian spring-summer (taiga) – A84.0
    - specified NEC – A84.89
- specified type NEC – A85.8
- tick-borne, specified NEC – A84.89
Western equine – A83.1

How to choose the right code

Start with the main term, then pick the indented subterm that matches the documentation (type, cause, site, laterality, episode of care). Always confirm the code in the tabular list: follow its Excludes1/Excludes2, “code first” and “use additional code” notes, and add a 7th character where required.

Source: CDC/NCHS ICD-10-CM FY2027 alphabetic index.