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  3. A00–B99
  4. A80-A89
  5. Atypical virus infections of central nervous system (A81)

Atypical virus infections of central nervous system (A81)

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.

Instructional Notations

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.

Clinical Terms

The following clinical terms provide additional context, helping users better understand the clinical background and common associations for each diagnosis listed in this section. Including related terms alongside ICD-10-CM codes supports coders, billers, and healthcare professionals in improving accuracy, enhancing documentation, and facilitating research or patient education.

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)