2026 ICD-10-CM Diagnosis Code A81.83Fatal familial insomnia

ICD-10-CM Codes›A00–B99›A80-A89›A81

ICD-10-CM A81.83
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A81.83 is a billable ICD-10-CM diagnosis code for fatal familial insomnia. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 974 through 976. Coders also document this condition as dementia due to fatal familial insomnia. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified CNS infection and poliomyelitis and Viral infection.

Code Identity

ICD-10-CM Code
A81.83
Billable Status
Yes — Valid for Submission
Code Describes
Fatal familial insomnia
Short Description
Fatal familial insomnia
Same as the full description in the CMS dataset.
Parent Code
A81.8
Other atypical virus infections of central nervous system

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA80-A89Viral and prion infections of the central nervous system
CategoryA81Atypical virus infections of central nervous system
This CodeA81.83Fatal familial insomnia

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Dementia due to fatal familial insomnia
  • Dementia due to genetic disease
  • Dementia due to prion disease
  • Fatal familial insomnia

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • FFI

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Insomnia(organic)
      • fatal familial (FFI)

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NVS003
Other specified CNS infection and poliomyelitis
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR INF008
Viral infection
Default principal diagnosis: inpatient No · outpatient No

Clinical InformationClinical

  • Fatal Familial Insomnia

    a very rare autosomal dominant inherited sleep disorder caused by a mutation in the gene responsible for the prion protein. it affects individuals usually in their fourth decade. its initial manifestation is difficulty in falling asleep. it is followed by complete inability to sleep. patients develop deterioration of their mental and motor functions and die soon after the first symptoms appear, because of the total absence of sleep.

  • PRNP Gene|PRNP|PRNP|Prion Protein (p27-30) (Creutzfeldt-Jakob Disease, Gerstmann-Strausler-Scheinker Syndrome, Fatal Familial Insomnia) Gene

    this gene is involved in prion diseases.

  • PRNP wt Allele|ASCR|CD230|CJD|GSS|MGC26679|PRIP|PrP|PrP27-30|PrP33-35C|PrPc|Prion Protein (p27-30) (Creutzfeldt-Jakob Disease, Gerstmann-Strausler-Scheinker Syndrome, Fatal Familial Insomnia) wt Allele

    human prnp wild-type allele is located in the vicinity of 20p13 and is approximately 15 kb in length. this allele, which encodes major prion protein, plays a role in both the extracellular surface and the development of prion diseases. mutations in the gene are associated with inherited transmissible spongiform encephalopathies.

Patient EducationClinical

Degenerative Nerve Diseases

Degenerative nerve diseases affect many of your body's activities, such as balance, movement, talking, breathing, and heart function. Many of these diseases are genetic. Sometimes the cause is a medical condition such as alcoholism, a tumor, or a stroke. Other causes may include toxins, chemicals, and viruses.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert A81.83 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
046.72 Fatal familial insomnia
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About A81.83Overview

Is A81.83 (Other atypical virus infections of central nervous system) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report fatal familial insomnia on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does A81.83 group to?

When fatal familial insomnia is the principal diagnosis on an inpatient stay, it groups to MS-DRG 974, 975, 976, with relative weights from 0.8945 to 2.8860 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of A81.83?

Under the General Equivalence Mappings, fatal familial insomnia converts to ICD-9-CM 046.72 (fatal familial insomnia). The mapping is a direct match.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.