Atypical virus infections of central nervous system (A81) ICD-10-CM
The A81 code range covers atypical virus infections of central nervous system with 13 ICD-10-CM diagnosis codes. 10 of them are billable and valid for claim submission in fiscal year 2026, and the category headers group them but cannot themselves be billed.
Includes
This note appears immediately under a three character code title to further define, or give examples of, the content of the category.
- diseases of the central nervous system caused by prions
Use Additional Code
The “use additional code” indicates that a secondary code could be used to further specify the patient’s condition. This note is not mandatory and is only used if enough information is available to assign an additional code.
- code, if applicable, to identify:
- dementia with anxiety F02.84 F02.A4 F02.B4 F02.C4
- dementia with behavioral disturbance F02.81 F02.A1 F02.B1 F02.C1
- dementia with mood disturbance F02.83 F02.A3 F02.B3 F02.C3
- dementia with psychotic disturbance F02.82 F02.A2 F02.B2 F02.C2
- dementia without behavioral disturbance F02.80 F02.A0 F02.B0 F02.C0
- mild neurocognitive disorder due to known physiological condition F06.7
Codes in the A81 Range 13 codes · 10 billable
- A81 Atypical virus infections of central nervous systemNon-billable
- A81.0 Creutzfeldt-Jakob diseaseNon-billable
- A81.00 Creutzfeldt-Jakob disease, unspecified
- A81.01 Variant Creutzfeldt-Jakob disease
- A81.09 Other Creutzfeldt-Jakob disease
- A81.1 Subacute sclerosing panencephalitis
- A81.2 Progressive multifocal leukoencephalopathy
- A81.8 Other atypical virus infections of central nervous systemNon-billable
- A81.81 Kuru
- A81.82 Gerstmann-Straussler-Scheinker syndrome
- A81.83 Fatal familial insomnia
- A81.89 Other atypical virus infections of central nervous system
- A81.9 Atypical virus infection of central nervous system, unspecified
Clinical Terms in This Code Range
Definitions from the National Library of Medicine for conditions coded in the A81 range.
Kuru
A prion disease found exclusively among the Fore linguistic group natives of the highlands of NEW GUINEA. The illness is primarily restricted to adult females and children of both sexes. It is marked by the subacute onset of tremor and ataxia followed by motor weakness and incontinence. Death occurs within 3-6 months of disease onset. The condition is associated with ritual cannibalism, and has become rare since this practice has been discontinued. Pathologic features include a noninflammatory loss of neurons that is most prominent in the cerebellum, glial proliferation, and amyloid plaques. (From Adams et al., Principles of Neurology, 6th ed, p773)
New Guinea
Originally an island of the Malay Archipelago, the second largest island in the world. It divided, West New Guinea becoming part of Indonesia and East New Guinea becoming Papua New Guinea.
Subacute Sclerosing Panencephalitis
A rare, slowly progressive encephalitis caused by chronic infection with the MEASLES VIRUS. The condition occurs primarily in children and young adults, approximately 2-8 years after the initial infection. A gradual decline in intellectual abilities and behavioral alterations are followed by progressive MYOCLONUS; MUSCLE SPASTICITY; SEIZURES; DEMENTIA; autonomic dysfunction; and ATAXIA. DEATH usually occurs 1-3 years after disease onset. Pathologic features include perivascular cuffing, eosinophilic cytoplasmic inclusions, neurophagia, and fibrous gliosis. It is caused by the SSPE virus, which is a defective variant of MEASLES VIRUS. (From Adams et al., Principles of Neurology, 6th ed, pp767-8)
About the A81 Code Range
The ICD-10 code A81 covers atypical virus infections of the central nervous system, including rare and serious neurological conditions caused by prions and similar agents. These codes identify diseases such as Creutzfeldt-Jakob disease and progressive multifocal leukoencephalopathy, essential for accurately documenting unusual viral infections affecting the brain.
This section includes specific codes like A81.0 for Creutzfeldt-Jakob disease (CJD), which has variants such as A81.00 unspecified CJD, A81.01 variant CJD, and other forms in A81.09. These conditions are synonymous with terms like “dementia due to prion disease” or “spongiform encephalopathy,” helping coders connect common diagnostic phrases with the correct ICD-10 code. Other notable codes are A81.1 for subacute sclerosing panencephalitis—also known as post-measles encephalitis—and A81.2 for progressive multifocal leukoencephalopathy, often linked to HIV/AIDS and caused by the JC polyomavirus. Additional codes, such as A81.81 for Kuru and A81.83 for fatal familial insomnia, document rare prion-related diseases. A81.9 represents unspecified atypical viral CNS infections, encompassing a spectrum of prion-associated disorders, useful when precise diagnosis is unavailable.
Questions About This Page
How many billable codes are in the A81 range?
Of the 13 codes in this range, 10 are billable and valid for claim submission from October 1, 2025 through September 30, 2026. Category header codes group them but cannot be reported on claims.
What does the A81 range classify?
The range classifies atypical virus infections of central nervous system. Each code links to its own reference page with billing status, MS-DRG grouping, coding notes, and clinical information.
Related References
Source: CMS FY 2026 ICD-10-CM Tabular List and order file, effective October 1, 2025 through September 30, 2026.
