A81.83
Fatal familial insomnia
A81.83 (also written A8183) is a billable ICD-10-CM diagnosis code for fatal familial insomnia. It is part of the FY2027 code set, effective October 1, 2026. It is one of the 10 codes in category A81 (Atypical virus infections of central nervous system). The Alphabetic Index lists it under 1 entry. Its coding notes include a Use additional code instruction, 3 Excludes1 entries and 5 Excludes2 entries.
Use additional code
Add the listed code as a secondary code, if known.
- 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-)
Excludes1
Not coded here. The listed conditions generally should not be reported together.
Excludes2
Not included here. Both codes may be reported if the patient has both conditions.
Also from chapter/block level (5 notes)
- carrier or suspected carrier of infectious disease (Z22.-)
- certain localized infections - see body system-related chapters
- infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
- infectious and parasitic diseases specific to the perinatal period (P35-P39)
- influenza and other acute respiratory infections (J00-J22)
Care settings
How CMS programs treat this code. These are CMS claim edits and list entries, not coverage or eligibility rules.
Home Health Primary
Accepted as the primary (principal) diagnosis on a home health claim. The Home Health Grouper assigns it to the Neuro Rehabilitation clinical group.
Source: CMS Home Health Grouper Software v07.2.26, effective October 1, 2026Hospital CC
Counts as a complication or comorbidity (CC) when reported as a secondary diagnosis on an inpatient claim. It does not count when the principal diagnosis is one of the 15 codes in its exclusion list. Some MS-DRGs also ignore a CC or MCC that defines the DRG.
Source: CMS MS-DRG Definitions Manual v44, effective October 1, 2026, Appendix CIPF Primary
IPF MS-DRG adjustment. A principal diagnosis of this code groups to one of these MS-DRGs. Which one depends on other facts of the stay, so the factor is a range:
| MS-DRG | Description | Factor |
|---|---|---|
| 056 | Degenerative nervous system disorders w MCC | 1.12 |
| 057 | Degenerative nervous system disorders w/o MCC | 1.11 |
Includes
Further defines or gives examples of the content of the category.
- diseases of the central nervous system caused by prions
Also from chapter/block level (1 note)
- diseases generally recognized as communicable or transmissible
Inclusion terms
Conditions classified to this code.
- FFI
Alphabetic Index terms
Terms the official Alphabetic Index lists for this code. 1 entry