All ICD10 Codes
A81Not billable, use a more specific code below

Atypical virus infections of central nervous system

In Viral and prion infections of the central nervous system (A80-A89), chapter 1: Certain Infectious and Parasitic Diseases

10 billable codes under A81: all are a CC; all map to HCC 127 (Dementia, Mild or Unspecified).A CC or MCC (major CC) is a secondary diagnosis that raises the MS-DRG payment. An HCC counts toward a Medicare Advantage patient's risk score.

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Instructional notes

Includes: conditions that are coded here

  • diseases of the central nervous system caused by prions

Use additional code: add a second code for this, listed after this one

Also applies, from Viral and prion infections of the central nervous system (A80-A89)

These notes sit on A80-A89 and apply to every code under it, including A81.

Excludes1: not coded here, use a different code

  • postpolio syndrome (G14)
  • sequelae of poliomyelitis (B91)
  • sequelae of viral encephalitis (B94.1)

Official coding guidelines

From the ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027 (CMS and NCHS). Links open the PDF at the right page.

Rules for coding infections and parasitic diseases, including HIV, organism and drug resistance codes, sepsis and septic shock, MRSA, Zika, and COVID-19.

Read Section I.C.1 (page 19)

All codes under A81

A81 can't be used on a claim. Pick a billable code below; grey headings group them.

A81 MS-DRGs

As the principal diagnosis, the billable codes under A81 group to these 7 MS-DRGs (v44.0). Which one applies depends on procedures performed, secondary diagnoses (CC/MCC), and the patient's age and discharge status.

About the condition

Plain-language background from MedlinePlus (National Library of Medicine), not coding guidance.

Neurologic Diseases

The brain, spinal cord, and nerves make up the nervous system. Together they control all the workings of the body. When something goes wrong with a part of your nervous system, you can have trouble moving, speaking, swallowing, breathing, or learning. You can also have problems with your memory, senses, or mood.

Read more about neurologic diseases on MedlinePlus

Viral Infections

Viruses are very tiny germs. They are made of genetic material (either DNA or RNA) inside of a protein coating. There are a huge number of viruses on earth. Only a small number of them can infect humans. Those viruses can infect our cells, which may cause disease. Some of the diseases that viruses can cause include the common cold, the flu, COVID-19, and HIV.

Read more about viral infections on MedlinePlus

Code history

Valid since FY2016, when ICD-10-CM took effect on October 1, 2015. No changes since.