ICD10BillableValid for clinical use
ICD-10 Code A81.9: Atypical virus infection of central nervous system, unspecified
Reviewed by HealthAssure Clinical TeamUpdated 26 May 2026
What is this code?
ICD-10 codes are diagnosis classification codes used in healthcare records, reporting, coding workflows, and billing support. This code sits within the broader ICD-10 area for Certain infectious and parasitic diseases (A00-B99).
When is it used?
- May be used when a clinician documents atypical virus infection of central nervous system, unspecified in a patient's medical record.
- May appear in hospital records, claims, referrals, and clinical documentation.
- This code can be used as a clinically usable diagnosis entry in standardized coding workflows.
What it does not mean
- A code alone does not explain severity, treatment plan, or outcome.
- A medical code should not be treated as a substitute for a doctor's diagnosis or advice.
Code hierarchy
chapter
1Certain infectious and parasitic diseases (A00-B99)
block
A80-A89Viral and prion infections of the central nervous system
category
A81Atypical virus infections of central nervous system
currentA81
Official coding notes
Inclusion terms
- Prion diseases of the central nervous system NOS
Where you may see this code
You may see this code in hospital records, discharge summaries, insurance claims, encounter documentation, referrals, or other healthcare billing and coding records.
Related specialists
Infectious Disease SpecialistGeneral Physician
Related codes
Sibling codes
Coverage-related procedures and services
CPT 70460high
COMPUTED TOMOGRAPHY, HEAD OR BRAIN; WITH CONTRAST MATERIAL(S)
Source: CMS coverage guidance
CPT 70450high
COMPUTED TOMOGRAPHY, HEAD OR BRAIN; WITHOUT CONTRAST MATERIAL
Source: CMS coverage guidance
CPT 70470high
COMPUTED TOMOGRAPHY, HEAD OR BRAIN; WITHOUT CONTRAST MATERIAL, FOLLOWED BY CONTRAST MATERIAL(S) AND FURTHER SECTIONS
Source: CMS coverage guidance
CPT 72126high
COMPUTED TOMOGRAPHY, CERVICAL SPINE; WITH CONTRAST MATERIAL
Source: CMS coverage guidance
CPT 72125high
COMPUTED TOMOGRAPHY, CERVICAL SPINE; WITHOUT CONTRAST MATERIAL
Source: CMS coverage guidance
CPT 72127high
COMPUTED TOMOGRAPHY, CERVICAL SPINE; WITHOUT CONTRAST MATERIAL, FOLLOWED BY CONTRAST MATERIAL(S) AND FURTHER SECTIONS
Source: CMS coverage guidance
Mapped diagnoses and classifications
SNOMED_CT 721255002high
Acquired prion disease
Source: SNOMED International ICD-10 map
SNOMED_CT 1259081008high
Autonomic disorder due to prion disease
Source: SNOMED International ICD-10 map
SNOMED_CT 762350007high
Dementia due to prion disease
Source: SNOMED International ICD-10 map
SNOMED_CT 1176989007high
Parkinsonism due to prion disease
Source: SNOMED International ICD-10 map
SNOMED_CT 20484008high
Prion disease
Source: SNOMED International ICD-10 map
SNOMED_CT 186482006high
Slow viral central nervous system infection
Source: SNOMED International ICD-10 map
Coding guidelines
Compatibility
Legacy and official ICD code match exactly.
Legacy codes
A81.9
Common synonyms
Atypical virus infection of central nervous system, unspecifiedAtypical virus infection of central nervous system
Frequently asked questions
About this content
This page is prepared by HealthAssure's clinical team using official coding standards from ICD-10. AI tools assist with drafting explanations, which are then reviewed and verified by healthcare professionals for accuracy. This content is for informational purposes and does not replace professional medical advice. Meet our team.